Applications

1 - Specifying a Disruption Budget for Kubernetes Controllers

Introduction of Disruptions

We need to understand that some kind of voluntary disruptions can happen to pods. For example, they can be caused by cluster administrators who want to perform automated cluster actions, like upgrading and autoscaling clusters. Typical application owner actions include:

• deleting the deployment or other controller that manages the pod
• updating a deployment’s pod template causing a restart
• directly deleting a pod (e.g., by accident)

Setup Pod Disruption Budgets

Kubernetes offers a feature called PodDisruptionBudget (PDB) for each application. A PDB limits the number of pods of a replicated application that are down simultaneously from voluntary disruptions.

The most common use case is when you want to protect an application specified by one of the built-in Kubernetes controllers:

• Deployment
• ReplicationController
• ReplicaSet
• StatefulSet

A PodDisruptionBudget has three fields:

• A label selector .spec.selector to specify the set of pods to which it applies.
• .spec.minAvailable which is a description of the number of pods from that set that must still be available after the eviction, even in the absence of the evicted pod. minAvailable can be either an absolute number or a percentage.
• .spec.maxUnavailable which is a description of the number of pods from that set that can be unavailable after the eviction. It can be either an absolute number or a percentage.

Cluster Upgrade or Node Deletion Failed due to PDB Violation:

Misconfiguration of the PDB could block the cluster upgrade or node deletion processes. There are two main cases that can cause a misconfiguration.

Case 1: The replica of Kubernetes controllers is 1

• Only 1 replica is running: there is no replicaCount setup or replicaCount for the Kubernetes controllers is set to 1
• PDB configuration

    spec:
      minAvailable: 1
  

• To fix this PDB misconfiguration, you need to change the value of replicaCount for the Kubernetes controllers to a number greater than 1

Case 2: HPA configuration violates PDB

In Kubernetes, a HorizontalPodAutoscaler automatically updates a workload resource (such as a Deployment or StatefulSet), with the aim of automatically scaling the workload to match demand. The HorizontalPodAutoscaler manages the replicas field of the Kubernetes controllers.

• There is no replicaCount setup or replicaCount for the Kubernetes controllers is set to 1
• PDB configuration

    spec:
      minAvailable: 1
  

• HPA configuration

    spec:
      minReplicas: 1
  

• To fix this PDB misconfiguration, you need to change the value of HPA minReplicas to be greater than 1

Related Links

• Specifying a Disruption Budget for Your Application
• Horizontal Pod Autoscaling

2 - Access a Port of a Pod Locally

Question

You have deployed an application with a web UI or an internal endpoint in your Kubernetes (K8s) cluster. How to access this endpoint without an external load balancer (e.g. Ingress)?

This tutorial presents two options:

• Using Kubernetes port forward
• Using Kubernetes apiserver proxy

Please note that the options described here are mostly for quick testing or troubleshooting your application. For enabling access to your application for productive environment, please refer to the official Kubernetes documentation.

Solution 1: Using Kubernetes port forward

You could use the port forwarding functionality of kubectl to access the pods from your local host without involving a service.

To access any pod follow these steps:

1. Run kubectl get pods
2. Note down the name of the pod in question as <your-pod-name>
3. Run kubectl port-forward <your-pod-name> <local-port>:<your-app-port>
4. Run a web browser or curl locally and enter the URL: http(s)://localhost:<local-port>

In addition, kubectl port-forward allows using a resource name, such as a deployment name or service name, to select a matching pod to port forward. More details can be found in the Kubernetes documentation.

The main drawback of this approach is that the pod’s name changes as soon as it is restarted. Moreover, you need to have a web browser on your client and you need to make sure that the local port is not already used by an application running on your system. Finally, sometimes the port forwarding is canceled due to nonobvious reasons. This leads to a kind of shaky approach. A more stable possibility is based on accessing the app via the kube-proxy, which accesses the corresponding service.

Solution 2: Using the apiserver proxy of Your Kubernetes Cluster

There are several different proxies in Kubernetes. In this tutorial we will be using apiserver proxy to enable the access to the services in your cluster without Ingress. Unlike the first solution, here a service is required.

Use the following format to compose a URL for accessing your service through an existing proxy on the Kubernetes cluster:

https://<your-cluster-master>/api/v1/namespace/<your-namespace>/services/<your-service>:<your-service-port>/proxy/<service-endpoint>

Example:

For more details on the format, please refer to the official Kubernetes documentation.

3 - Auditing Kubernetes for Secure Setup

Increasing the Security of All Gardener Stakeholders

In summer 2018, the Gardener project team asked Kinvolk to execute several penetration tests in its role as third-party contractor. The goal of this ongoing work was to increase the security of all Gardener stakeholders in the open source community. Following the Gardener architecture, the control plane of a Gardener managed shoot cluster resides in the corresponding seed cluster. This is a Control-Plane-as-a-Service with a network air gap.

Along the way we found various kinds of security issues, for example, due to misconfiguration or missing isolation, as well as two special problems with upstream Kubernetes and its Control-Plane-as-a-Service architecture.

Major Findings

From this experience, we’d like to share a few examples of security issues that could happen on a Kubernetes installation and how to fix them.

Alban Crequy (Kinvolk) and Dirk Marwinski (SAP SE) gave a presentation entitled Hardening Multi-Cloud Kubernetes Clusters as a Service at KubeCon 2018 in Shanghai presenting some of the findings.

Here is a summary of the findings:

• Privilege escalation due to insecure configuration of the Kubernetes API server

  • Root cause: Same certificate authority (CA) is used for both the API server and the proxy that allows accessing the API server.
  • Risk: Users can get access to the API server.
  • Recommendation: Always use different CAs.

• Exploration of the control plane network with malicious HTTP-redirects

  • Root cause: See detailed description below.

  • Risk: Provoked error message contains full HTTP payload from an existing endpoint which can be exploited. The contents of the payload depends on your setup, but can potentially be user data, configuration data, and credentials.

  • Recommendation:

    • Use the latest version of Gardener
    • Ensure the seed cluster’s container network supports network policies. Clusters that have been created with Kubify are not protected as Flannel is used there which doesn’t support network policies.

• Reading private AWS metadata via Grafana

  • Root cause: It is possible to configuring a new custom data source in Grafana, we could send HTTP requests to target the control
  • Risk: Users can get the “user-data” for the seed cluster from the metadata service and retrieve a kubeconfig for that Kubernetes cluster
  • Recommendation: Lockdown Grafana features to only what’s necessary in this setup, block all unnecessary outgoing traffic, move Grafana to a different network, lockdown unauthenticated endpoints

Scenario 1: Privilege Escalation with Insecure API Server

In most configurations, different components connect directly to the Kubernetes API server, often using a kubeconfig with a client certificate. The API server is started with the flag:

/hyperkube apiserver --client-ca-file=/srv/kubernetes/ca/ca.crt ...

The API server will check whether the client certificate presented by kubectl, kubelet, scheduler or another component is really signed by the configured certificate authority for clients.

The API server can have many clients of various kinds

However, it is possible to configure the API server differently for use with an intermediate authenticating proxy. The proxy will authenticate the client with its own custom method and then issue HTTP requests to the API server with additional HTTP headers specifying the user name and group name. The API server should only accept HTTP requests with HTTP headers from a legitimate proxy. To allow the API server to check incoming requests, you need pass on a list of certificate authorities (CAs) to it. Requests coming from a proxy are only accepted if they use a client certificate that is signed by one of the CAs of that list.

--requestheader-client-ca-file=/srv/kubernetes/ca/ca-proxy.crt
--requestheader-username-headers=X-Remote-User
--requestheader-group-headers=X-Remote-Group

API server clients can reach the API server through an authenticating proxy

So far, so good. But what happens if the malicious user “Mallory” tries to connect directly to the API server and reuses the HTTP headers to pretend to be someone else?

What happens when a client bypasses the proxy, connecting directly to the API server?

With a correct configuration, Mallory’s kubeconfig will have a certificate signed by the API server certificate authority but not signed by the proxy certificate authority. So the API server will not accept the extra HTTP header “X-Remote-Group: system:masters”.

You only run into an issue when the same certificate authority is used for both the API server and the proxy. Then, any Kubernetes client certificate can be used to take the role of different user or group as the API server will accept the user header and group header.

The kubectl tool does not normally add those HTTP headers but it’s pretty easy to generate the corresponding HTTP requests manually.

We worked on improving the Kubernetes documentation to make clearer that this configuration should be avoided.

Scenario 2: Exploration of the Control Plane Network with Malicious HTTP-Redirects

The API server is a central component of Kubernetes and many components initiate connections to it, including the kubelet running on worker nodes. Most of the requests from those clients will end up updating Kubernetes objects (pods, services, deployments, and so on) in the etcd database but the API server usually does not need to initiate TCP connections itself.

The API server is mostly a component that receives requests

However, there are exceptions. Some kubectl commands will trigger the API server to open a new connection to the kubelet. kubectl exec is one of those commands. In order to get the standard I/Os from the pod, the API server will start an HTTP connection to the kubelet on the worker node where the pod is running. Depending on the container runtime used, it can be done in different ways, but one way to do it is for the kubelet to reply with a HTTP-302 redirection to the Container Runtime Interface (CRI). Basically, the kubelet is telling the API server to get the streams from CRI itself directly instead of forwarding. The redirection from the kubelet will only change the port and path from the URL; the IP address will not be changed because the kubelet and the CRI component run on the same worker node.

But the API server also initiates some connections, for example, to worker nodes

It’s often quite easy for users of a Kubernetes cluster to get access to worker nodes and tamper with the kubelet. They could be given explicit SSH access or they could be given a kubeconfig with enough privileges to create privileged pods or even just pods with “host” volumes.

In contrast, users (even those with “system:masters” permissions or “root” rights) are often not given access to the control plane. On setups like, for example, GKE or Gardener, the control plane is running on separate nodes, with a different administrative access. It could be hosted on a different cloud provider account. So users are not free to explore the internal network in the control plane.

What would happen if a user was tampering with the kubelet to make it maliciously redirect kubectl exec requests to a different random endpoint? Most likely the given endpoint would not speak to the streaming server protocol, so there would be an error. However, the full HTTP payload from the endpoint is included in the error message printed by kubectl exec.

The API server is tricked to connect to other components

The impact of this issue depends on the specific setup. But in many configurations, we could find a metadata service (such as the AWS metadata service) containing user data, configurations and credentials. The setup we explored had a different AWS account and a different EC2 instance profile for the worker nodes and the control plane. This issue allowed users to get access to the AWS metadata service in the context of the control plane, which they should not have access to.

We have reported this issue to the Kubernetes Security mailing list and the public pull request that addresses the issue has been merged PR#66516. It provides a way to enforce HTTP redirect validation (disabled by default).

But there are several other ways that users could trigger the API server to generate HTTP requests and get the reply payload back, so it is advised to isolate the API server and other components from the network as additional precautious measures. Depending on where the API server runs, it could be with Kubernetes Network Policies, EC2 Security Groups or just iptables directly. Following the defense in depth principle, it is a good idea to apply the API server HTTP redirect validation when it is available as well as firewall rules.

In Gardener, this has been fixed with Kubernetes network policies along with changes to ensure the API server does not need to contact the metadata service. You can see more details in the announcements on the Gardener mailing list. This is tracked in CVE-2018-2475.

To be protected from this issue, stakeholders should:

• Use the latest version of Gardener
• Ensure the seed cluster’s container network supports network policies. Clusters that have been created with Kubify are not protected as Flannel is used there which doesn’t support network policies.

Scenario 3: Reading Private AWS Metadata via Grafana

For our tests, we had access to a Kubernetes setup where users are not only given access to the API server in the control plane, but also to a Grafana instance that is used to gather data from their Kubernetes clusters via Prometheus. The control plane is managed and users don’t have access to the nodes that it runs. They can only access the API server and Grafana via a load balancer. The internal network of the control plane is therefore hidden to users.

Prometheus and Grafana can be used to monitor worker nodes

Unfortunately, that setup was not protecting the control plane network from nosy users. By configuring a new custom data source in Grafana, we could send HTTP requests to target the control plane network, for example the AWS metadata service. The reply payload is not displayed on the Grafana Web UI but it is possible to access it from the debugging console of the Chrome browser.

Credentials can be retrieved from the debugging console of Chrome

Adding a Grafana data source is a way to issue HTTP requests to arbitrary targets

In that installation, users could get the “user-data” for the seed cluster from the metadata service and retrieve a kubeconfig for that Kubernetes cluster.

There are many possible measures to avoid this situation: lockdown Grafana features to only what’s necessary in this setup, block all unnecessary outgoing traffic, move Grafana to a different network, or lockdown unauthenticated endpoints, among others.

Conclusion

The three scenarios above show pitfalls with a Kubernetes setup. A lot of them were specific to the Kubernetes installation: different cloud providers or different configurations will show different weaknesses. Users should no longer be given access to Grafana.

4 - Container Image Not Pulled

Problem

Two of the most common causes of this problems are specifying the wrong container image or trying to use private images without providing registry credentials.

Example

Let’s see an example. We’ll create a pod named fail, referencing a non-existent Docker image:

kubectl run -i --tty fail --image=tutum/curl:1.123456

The command doesn’t return and you can terminate the process with Ctrl+C.

Error Analysis

We can then inspect our pods and see that we have one pod with a status of ErrImagePull or ImagePullBackOff.

$ (minikube) kubectl get pods
NAME                      READY     STATUS         RESTARTS   AGE
client-5b65b6c866-cs4ch   1/1       Running        1          1m
fail-6667d7685d-7v6w8     0/1       ErrImagePull   0          <invalid>
vuejs-578574b75f-5x98z    1/1       Running        0          1d
$ (minikube) 

For some additional information, we can describe the failing pod.

kubectl describe pod fail-6667d7685d-7v6w8

As you can see in the events section, your image can’t be pulled:

Name:		fail-6667d7685d-7v6w8
Namespace:	default
Node:		minikube/192.168.64.10
Start Time:	Wed, 22 Nov 2017 10:01:59 +0100
Labels:		pod-template-hash=2223832418
		run=fail
Annotations:	kubernetes.io/created-by={"kind":"SerializedReference","apiVersion":"v1","reference":{"kind":"ReplicaSet","namespace":"default","name":"fail-6667d7685d","uid":"cc4ccb3f-cf63-11e7-afca-4a7a1fa05b3f","a...
.
.
.
.
Events:
  FirstSeen	LastSeen	Count	From			SubObjectPath		Type		Reason			Message
  ---------	--------	-----	----			-------------		--------	------			-------
  1m		1m		1	default-scheduler				Normal		Scheduled		Successfully assigned fail-6667d7685d-7v6w8 to minikube
  1m		1m		1	kubelet, minikube				Normal		SuccessfulMountVolume	MountVolume.SetUp succeeded for volume "default-token-9fr6r" 
  1m		6s		4	kubelet, minikube	spec.containers{fail}	Normal		Pulling			pulling image "tutum/curl:1.123456"
  1m		5s		4	kubelet, minikube	spec.containers{fail}	Warning		Failed			Failed to pull image "tutum/curl:1.123456": rpc error: code = Unknown desc = Error response from daemon: manifest for tutum/curl:1.123456 not found
  1m		<invalid>	10	kubelet, minikube				Warning		FailedSync		Error syncing pod
  1m		<invalid>	6	kubelet, minikube	spec.containers{fail}	Normal		BackOff			Back-off pulling image "tutum/curl:1.123456"

Why couldn’t Kubernetes pull the image? There are three primary candidates besides network connectivity issues:

• The image tag is incorrect
• The image doesn’t exist
• Kubernetes doesn’t have permissions to pull that image

If you don’t notice a typo in your image tag, then it’s time to test using your local machine. I usually start by running docker pull on my local development machine with the exact same image tag. In this case, I would run docker pull tutum/curl:1.123456.

If this succeeds, then it probably means that Kubernetes doesn’t have the correct permissions to pull that image.

Add the docker registry user/pwd to your cluster:

kubectl create secret docker-registry dockersecret --docker-server=https://index.docker.io/v1/ --docker-username=<username> --docker-password=<password> --docker-email=<email>

If the exact image tag fails, then I will test without an explicit image tag:

docker pull tutum/curl

This command will attempt to pull the latest tag. If this succeeds, then that means the originally specified tag doesn’t exist. Go to the Docker registry and check which tags are available for this image.

If docker pull tutum/curl (without an exact tag) fails, then we have a bigger problem - that image does not exist at all in our image registry.

5 - Container Image Not Updating

Introduction

A container image should use a fixed tag or the SHA of the image. It should not use the tags latest, head, canary, or other tags that are designed to be floating.

Problem

If you have encountered this issue, you have probably done something along the lines of:

• Deploy anything using an image tag (e.g. cp-enablement/awesomeapp:1.0)
• Fix a bug in awesomeapp
• Build a new image and push it with the same tag (cp-enablement/awesomeapp:1.0)
• Update the deployment
• Realize that the bug is still present
• Repeat steps 3-5 without any improvement

The problem relates to how Kubernetes decides whether to do a docker pull when starting a container. Since we tagged our image as :1.0, the default pull policy is IfNotPresent. The Kubelet already has a local copy of cp-enablement/awesomeapp:1.0, so it doesn’t attempt to do a docker pull. When the new Pods come up, they’re still using the old broken Docker image.

There are a couple of ways to resolve this, with the recommended one being to use unique tags.

Solution

In order to fix the problem, you can use the following bash script that runs anytime the deployment is updated to create a new tag and push it to the registry.

#!/usr/bin/env bash

# Set the docker image name and the corresponding repository
# Ensure that you change them in the deployment.yml as well.
# You must be logged in with docker login.
#
# CHANGE THIS TO YOUR Docker.io SETTINGS
#
PROJECT=awesomeapp
REPOSITORY=cp-enablement

# causes the shell to exit if any subcommand or pipeline returns a non-zero status.
#
set -e

# set debug mode
#
set -x

# build my nodeJS app
#
npm run build

# get the latest version ID from the Docker.io registry and increment them
#
VERSION=$(curl https://registry.hub.docker.com/v1/repositories/$REPOSITORY/$PROJECT/tags  | sed -e 's/[][]//g' -e 's/"//g' -e 's/ //g' | tr '}' '\n'  | awk -F: '{print $3}' | grep v| tail -n 1)
VERSION=${VERSION:1}
((VERSION++))
VERSION="v$VERSION"


# build the new docker image
#
echo '>>> Building new image'

echo '>>> Push new image'
docker push $REPOSITORY/$PROJECT:$VERSION

6 - Custom Seccomp Profile

Overview

Seccomp (secure computing mode) is a security facility in the Linux kernel for restricting the set of system calls applications can make.

Starting from Kubernetes v1.3.0, the Seccomp feature is in Alpha. To configure it on a Pod, the following annotations can be used:

• seccomp.security.alpha.kubernetes.io/pod: <seccomp-profile> where <seccomp-profile> is the seccomp profile to apply to all containers in a Pod.
• container.seccomp.security.alpha.kubernetes.io/<container-name>: <seccomp-profile> where <seccomp-profile> is the seccomp profile to apply to <container-name> in a Pod.

More details can be found in the PodSecurityPolicy documentation.

Installation of a Custom Profile

By default, kubelet loads custom Seccomp profiles from /var/lib/kubelet/seccomp/. There are two ways in which Seccomp profiles can be added to a Node:

• to be baked in the machine image
• to be added at runtime

This guide focuses on creating those profiles via a DaemonSet.

Create a file called seccomp-profile.yaml with the following content:

apiVersion: v1
kind: ConfigMap
metadata:
  name: seccomp-profile
  namespace: kube-system
data:
  my-profile.json: |
    {
      "defaultAction": "SCMP_ACT_ALLOW",
      "syscalls": [
        {
          "name": "chmod",
          "action": "SCMP_ACT_ERRNO"
        }
      ]
    }    

Apply the ConfigMap in your cluster:

$ kubectl apply -f seccomp-profile.yaml
configmap/seccomp-profile created

The next steps is to create the DaemonSet Seccomp installer. It’s going to copy the policy from above in /var/lib/kubelet/seccomp/my-profile.json.

Create a file called seccomp-installer.yaml with the following content:

apiVersion: apps/v1
kind: DaemonSet
metadata:
  name: seccomp
  namespace: kube-system
  labels:
    security: seccomp
spec:
  selector:
    matchLabels:
      security: seccomp
  template:
    metadata:
      labels:
        security: seccomp
    spec:
      initContainers:
      - name: installer
        image: alpine:3.10.0
        command: ["/bin/sh", "-c", "cp -r -L /seccomp/*.json /host/seccomp/"]
        volumeMounts:
        - name: profiles
          mountPath: /seccomp
        - name: hostseccomp
          mountPath: /host/seccomp
          readOnly: false
      containers:
      - name: pause
        image: k8s.gcr.io/pause:3.1
      terminationGracePeriodSeconds: 5
      volumes:
      - name: hostseccomp
        hostPath:
          path: /var/lib/kubelet/seccomp
      - name: profiles
        configMap:
          name: seccomp-profile

Create the installer and wait until it’s ready on all Nodes:

$ kubectl apply -f seccomp-installer.yaml
daemonset.apps/seccomp-installer created

$ kubectl -n kube-system get pods -l security=seccomp
NAME                      READY   STATUS    RESTARTS   AGE
seccomp-installer-wjbxq   1/1     Running   0          21s

Create a Pod Using a Custom Seccomp Profile

Finally, we want to create a profile which uses our new Seccomp profile my-profile.json.

Create a file called my-seccomp-pod.yaml with the following content:

apiVersion: v1
kind: Pod
metadata:
  name: seccomp-app
  namespace: default
  annotations:
    seccomp.security.alpha.kubernetes.io/pod: "localhost/my-profile.json"
    # you can specify seccomp profile per container. If you add another profile you can configure
    # it for a specific container - 'pause' in this case.
    # container.seccomp.security.alpha.kubernetes.io/pause: "localhost/some-other-profile.json"
spec:
  containers:
  - name: pause
    image: k8s.gcr.io/pause:3.1

Create the Pod and see that it’s running:

$ kubectl apply -f my-seccomp-pod.yaml
pod/seccomp-app created

$ kubectl get pod seccomp-app
NAME         READY   STATUS    RESTARTS   AGE
seccomp-app  1/1     Running   0          42s

Throubleshooting

If an invalid or a non-existing profile is used, then the Pod will be stuck in ContainerCreating phase:

broken-seccomp-pod.yaml:

apiVersion: v1
kind: Pod
metadata:
  name: broken-seccomp
  namespace: default
  annotations:
    seccomp.security.alpha.kubernetes.io/pod: "localhost/not-existing-profile.json"
spec:
  containers:
  - name: pause
    image: k8s.gcr.io/pause:3.1

$ kubectl apply -f broken-seccomp-pod.yaml
pod/broken-seccomp created

$ kubectl get pod broken-seccomp
NAME            READY   STATUS              RESTARTS   AGE
broken-seccomp  1/1     ContainerCreating   0          2m

$ kubectl describe pod broken-seccomp
Name:               broken-seccomp
Namespace:          default
....
Events:
  Type     Reason                  Age               From                     Message
  ----     ------                  ----              ----                     -------
  Normal   Scheduled               18s               default-scheduler        Successfully assigned kube-system/broken-seccomp to docker-desktop
  Warning  FailedCreatePodSandBox  4s (x2 over 18s)  kubelet, docker-desktop  Failed create pod sandbox: rpc error: code = Unknown desc = failed to make sandbox docker config for pod "broken-seccomp": failed to generate sandbox security options
for sandbox "broken-seccomp": failed to generate seccomp security options for container: cannot load seccomp profile "/var/lib/kubelet/seccomp/not-existing-profile.json": open /var/lib/kubelet/seccomp/not-existing-profile.json: no such file or directory

Related Links

• Seccomp
• A Seccomp Overview
• Seccomp Security Profiles for Docker
• Using Seccomp to Limit the Kernel Attack Surface

7 - Dockerfile Pitfalls

Using the latest Tag for an Image

Many Dockerfiles use the FROM package:latest pattern at the top of their Dockerfiles to pull the latest image from a Docker registry.

Bad Dockerfile

FROM alpine

While simple, using the latest tag for an image means that your build can suddenly break if that image gets updated. This can lead to problems where everything builds fine locally (because your local cache thinks it is the latest), while a build server may fail, because some pipelines make a clean pull on every build. Additionally, troubleshooting can prove to be difficult, since the maintainer of the Dockerfile didn’t actually make any changes.

Good Dockerfile

A digest takes the place of the tag when pulling an image. This will ensure that your Dockerfile remains immutable.

FROM alpine@sha256:7043076348bf5040220df6ad703798fd8593a0918d06d3ce30c6c93be117e430

Running apt/apk/yum update

Running apt-get install is one of those things virtually every Debian-based Dockerfile will have to do in order to satiate some external package requirements your code needs to run. However, using apt-get as an example, this comes with its own problems.

apt-get upgrade

This will update all your packages to their latests versions, which can be bad because it prevents your Dockerfile from creating consistent, immutable builds.

apt-get update (in a different line than the one running your apt-get install command)

Running apt-get update as a single line entry will get cached by the build and won’t actually run every time you need to run apt-get install. Instead, make sure you run apt-get update in the same line with all the packages to ensure that all are updated correctly.

Avoid Big Container Images

Building a small container image will reduce the time needed to start or restart pods. An image based on the popular Alpine Linux project is much smaller than most distribution based images (~5MB). For most popular languages and products, there is usually an official Alpine Linux image, e.g. golang, nodejs, and postgres.

$  docker images
REPOSITORY                                                      TAG                     IMAGE ID            CREATED             SIZE
postgres                                                        9.6.9-alpine            6583932564f8        13 days ago         39.26 MB
postgres                                                        9.6                     d92dad241eff        13 days ago         235.4 MB
postgres                                                        10.4-alpine             93797b0f31f4        13 days ago         39.56 MB

In addition, for compiled languages such as Go or C++ that do not require build time tooling during runtime, it is recommended to avoid build time tooling in the final images. With Docker’s support for multi-stages builds, this can be easily achieved with minimal effort. Such an example can be found at Multi-stage builds.

Google’s distroless image is also a good base image.

8 - Dynamic Volume Provisioning

Overview

The example shows how to run a Postgres database on Kubernetes and how to dynamically provision and mount the storage volumes needed by the database

Run Postgres Database

Define the following Kubernetes resources in a yaml file:

• PersistentVolumeClaim (PVC)
• Deployment

PersistentVolumeClaim

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: postgresdb-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 9Gi
  storageClassName: 'default'

This defines a PVC using the storage class default. Storage classes abstract from the underlying storage provider as well as other parameters, like disk-type (e.g.; solid-state vs standard disks).

The default storage class has the annotation {“storageclass.kubernetes.io/is-default-class”:“true”}.

$ kubectl describe sc default
Name:            default
IsDefaultClass:  Yes
Annotations:     kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"storage.k8s.io/v1beta1","kind":"StorageClass","metadata":{"annotations":{"storageclass.kubernetes.io/is-default-class":"true"},"labels":{"addonmanager.kubernetes.io/mode":"Exists"},"name":"default","namespace":""},"parameters":{"type":"gp2"},"provisioner":"kubernetes.io/aws-ebs"}
,storageclass.kubernetes.io/is-default-class=true
Provisioner:           kubernetes.io/aws-ebs
Parameters:            type=gp2
AllowVolumeExpansion:  <unset>
MountOptions:          <none>
ReclaimPolicy:         Delete
VolumeBindingMode:     Immediate
Events:                <none>

A Persistent Volume is automatically created when it is dynamically provisioned. In the following example, the PVC is defined as “postgresdb-pvc”, and a corresponding PV “pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb” is created and associated with the PVC automatically.

$ kubectl create -f .\postgres_deployment.yaml
persistentvolumeclaim "postgresdb-pvc" created

$ kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                    STORAGECLASS   REASON    AGE
pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb   9Gi        RWO            Delete           Bound     default/postgresdb-pvc   default                  3s

$ kubectl get pvc
NAME             STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
postgresdb-pvc   Bound     pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb   9Gi        RWO            default        8s

Notice that the RECLAIM POLICY is Delete (default value), which is one of the two reclaim policies, the other one is Retain. (A third policy Recycle has been deprecated). In the case of Delete, the PV is deleted automatically when the PVC is removed, and the data on the PVC will also be lost.

On the other hand, a PV with Retain policy will not be deleted when the PVC is removed, and moved to Release status, so that data can be recovered by Administrators later.

You can use the kubectl patch command to change the reclaim policy as described in Change the Reclaim Policy of a PersistentVolume or use kubectl edit pv <pv-name> to edit it online as shown below:

$ kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                    STORAGECLASS   REASON    AGE
pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb   9Gi        RWO            Delete           Bound     default/postgresdb-pvc   default                  44m

# change the reclaim policy from "Delete" to "Retain"
$ kubectl edit pv pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb
persistentvolume "pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb" edited

# check the reclaim policy afterwards
$ kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                    STORAGECLASS   REASON    AGE
pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb   9Gi        RWO            Retain           Bound     default/postgresdb-pvc   default                  45m

Deployment

Once a PVC is created, you can use it in your container via volumes.persistentVolumeClaim.claimName. In the below example, the PVC postgresdb-pvc is mounted as readable and writable, and in volumeMounts two paths in the container are mounted to subfolders in the volume.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: postgres
  namespace: default
  labels:
    app: postgres
  annotations:
    deployment.kubernetes.io/revision: "1"
spec:
  replicas: 1
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
      maxSurge: 1
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      name: postgres
      labels:
        app: postgres
    spec:
      containers:
        - name: postgres
          image: "cpettech.docker.repositories.sap.ondemand.com/jtrack_postgres:howto"
          env:
            - name: POSTGRES_USER
              value: postgres
            - name: POSTGRES_PASSWORD
              value: p5FVqfuJFrM42cVX9muQXxrC3r8S9yn0zqWnFR6xCoPqxqVQ
            - name: POSTGRES_INITDB_XLOGDIR
              value: "/var/log/postgresql/logs"
          ports:
            - containerPort: 5432
          volumeMounts:
            - mountPath: /var/lib/postgresql/data
              name: postgre-db
              subPath: data     # https://github.com/kubernetes/website/pull/2292.  Solve the issue of crashing initdb due to non-empty directory (i.e. lost+found)
            - mountPath: /var/log/postgresql/logs
              name: postgre-db
              subPath: logs
      volumes:
        - name: postgre-db
          persistentVolumeClaim:
            claimName: postgresdb-pvc
            readOnly: false
      imagePullSecrets:
      - name: cpettechregistry

To check the mount points in the container:

$ kubectl get po
NAME                        READY     STATUS    RESTARTS   AGE
postgres-7f485fd768-c5jf9   1/1       Running   0          32m

$ kubectl exec -it postgres-7f485fd768-c5jf9 bash

root@postgres-7f485fd768-c5jf9:/# ls /var/lib/postgresql/data/
base    pg_clog       pg_dynshmem  pg_ident.conf  pg_multixact  pg_replslot  pg_snapshots  pg_stat_tmp  pg_tblspc    PG_VERSION  postgresql.auto.conf  postmaster.opts
global  pg_commit_ts  pg_hba.conf  pg_logical     pg_notify     pg_serial    pg_stat       pg_subtrans  pg_twophase  pg_xlog     postgresql.conf       postmaster.pid

root@postgres-7f485fd768-c5jf9:/# ls /var/log/postgresql/logs/
000000010000000000000001  archive_status

Deleting a PersistentVolumeClaim

In case of a Delete policy, deleting a PVC will also delete its associated PV. If Retain is the reclaim policy, the PV will change status from Bound to Released when the PVC is deleted.

# Check pvc and pv before deletion
$ kubectl get pvc
NAME             STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
postgresdb-pvc   Bound     pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb   9Gi        RWO            default        50m

$ kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                    STORAGECLASS   REASON    AGE
pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb   9Gi        RWO            Retain           Bound     default/postgresdb-pvc   default                  50m

# delete pvc
$ kubectl delete pvc postgresdb-pvc
persistentvolumeclaim "postgresdb-pvc" deleted

# pv changed to status "Released"
$ kubectl get pv
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS     CLAIM                    STORAGECLASS   REASON    AGE
pvc-06c81c30-72ea-11e8-ada2-aa3b2329c8bb   9Gi        RWO            Retain           Released   default/postgresdb-pvc   default                  51m

9 - Install Knative in Gardener Clusters

Overview

This guide walks you through the installation of the latest version of Knative using pre-built images on a Gardener created cluster environment. To set up your own Gardener, see the documentation or have a look at the landscape-setup-template project. To learn more about this open source project, read the blog on kubernetes.io.

Prerequsites

Knative requires a Kubernetes cluster v1.15 or newer.

Steps

Install and Configure kubectl

1. If you already have kubectl CLI, run kubectl version --short to check the version. You need v1.10 or newer. If your kubectl is older, follow the next step to install a newer version.

2. Install the kubectl CLI.

Access Gardener

1. Create a project in the Gardener dashboard. This will essentially create a Kubernetes namespace with the name garden-<my-project>.

2. Configure access to your Gardener project using a kubeconfig.

   If you are not the Gardener Administrator already, you can create a technical user in the Gardener dashboard. Go to the “Members” section and add a service account. You can then download the kubeconfig for your project. You can skip this step if you create your cluster using the user interface; it is only needed for programmatic access, make sure you set export KUBECONFIG=garden-my-project.yaml in your shell.

Creating a Kubernetes Cluster

You can create your cluster using kubectl CLI by providing a cluster specification yaml file. You can find an example for GCP in the gardener/gardener repository. Make sure the namespace matches that of your project. Then just apply the prepared so-called “shoot” cluster CRD with kubectl:

kubectl apply --filename my-cluster.yaml

The easier alternative is to create the cluster following the cluster creation wizard in the Gardener dashboard:

Configure kubectl for Your Cluster

You can now download the kubeconfig for your freshly created cluster in the Gardener dashboard or via the CLI as follows:

kubectl --namespace shoot--my-project--my-cluster get secret kubecfg --output jsonpath={.data.kubeconfig} | base64 --decode > my-cluster.yaml

This kubeconfig file has full administrators access to you cluster. For the rest of this guide, be sure you have export KUBECONFIG=my-cluster.yaml set.

Installing Istio

Knative depends on Istio. If your cloud platform offers a managed Istio installation, we recommend installing Istio that way, unless you need the ability to customize your installation.

Otherwise, see the Installing Istio for Knative guide to install Istio.

You must install Istio on your Kubernetes cluster before continuing with these instructions to install Knative.

Installing cluster-local-gateway for Serving Cluster-Internal Traffic

If you installed Istio, you can install a cluster-local-gateway within your Knative cluster so that you can serve cluster-internal traffic. If you want to configure your revisions to use routes that are visible only within your cluster, install and use the cluster-local-gateway.

Installing Knative

The following commands install all available Knative components as well as the standard set of observability plugins. Knative’s installation guide - Installing Knative.

1. If you are upgrading from Knative 0.3.x: Update your domain and static IP address to be associated with the LoadBalancer istio-ingressgateway instead of knative-ingressgateway. Then run the following to clean up leftover resources:

   kubectl delete svc knative-ingressgateway -n istio-system
   kubectl delete deploy knative-ingressgateway -n istio-system
   

   If you have the Knative Eventing Sources component installed, you will also need to delete the following resource before upgrading:

   kubectl delete statefulset/controller-manager -n knative-sources
   

   While the deletion of this resource during the upgrade process will not prevent modifications to Eventing Source resources, those changes will not be completed until the upgrade process finishes.

2. To install Knative, first install the CRDs by running the kubectl apply command once with the -l knative.dev/crd-install=true flag. This prevents race conditions during the install, which cause intermittent errors:

   kubectl apply --selector knative.dev/crd-install=true \
   --filename https://github.com/knative/serving/releases/download/v0.12.1/serving.yaml \
   --filename https://github.com/knative/eventing/releases/download/v0.12.1/eventing.yaml \
   --filename https://github.com/knative/serving/releases/download/v0.12.1/monitoring.yaml
   

3. To complete the installation of Knative and its dependencies, run the kubectl apply command again, this time without the --selector flag:

   kubectl apply --filename https://github.com/knative/serving/releases/download/v0.12.1/serving.yaml \
   --filename https://github.com/knative/eventing/releases/download/v0.12.1/eventing.yaml \
   --filename https://github.com/knative/serving/releases/download/v0.12.1/monitoring.yaml
   

4. Monitor the Knative components until all of the components show a STATUS of Running:

   kubectl get pods --namespace knative-serving
   kubectl get pods --namespace knative-eventing
   kubectl get pods --namespace knative-monitoring
   

Set Your Custom Domain

1. Fetch the external IP or CNAME of the knative-ingressgateway:

kubectl --namespace istio-system get service knative-ingressgateway
NAME                     TYPE           CLUSTER-IP      EXTERNAL-IP     PORT(S)                                      AGE
knative-ingressgateway   LoadBalancer   100.70.219.81   35.233.41.212   80:32380/TCP,443:32390/TCP,32400:32400/TCP   4d

2. Create a wildcard DNS entry in your custom domain to point to the above IP or CNAME:

*.knative.<my domain> == A 35.233.41.212
# or CNAME if you are on AWS
*.knative.<my domain> == CNAME a317a278525d111e89f272a164fd35fb-1510370581.eu-central-1.elb.amazonaws.com

3. Adapt your Knative config-domain (set your domain in the data field):

kubectl --namespace knative-serving get configmaps config-domain --output yaml
apiVersion: v1
data:
  knative.<my domain>: ""
kind: ConfigMap
  name: config-domain
  namespace: knative-serving

What’s Next

Now that your cluster has Knative installed, you can see what Knative has to offer.

Deploy your first app with the Getting Started with Knative App Deployment guide.

Get started with Knative Eventing by walking through one of the Eventing Samples.

Install Cert-Manager if you want to use the automatic TLS cert provisioning feature.

Cleaning Up

Use the Gardener dashboard to delete your cluster, or execute the following with kubectl pointing to your garden-my-project.yaml kubeconfig:

kubectl --kubeconfig garden-my-project.yaml --namespace garden--my-project annotate shoot my-cluster confirmation.gardener.cloud/deletion=true

kubectl --kubeconfig garden-my-project.yaml --namespace garden--my-project delete shoot my-cluster

10 - Integrity and Immutability

Introduction

When transferring data among networked systems, trust is a central concern. In particular, when communicating over an untrusted medium such as the internet, it is critical to ensure the integrity and immutability of all the data a system operates on. Especially if you use Docker Engine to push and pull images (data) to a public registry.

This immutability offers you a guarantee that any and all containers that you instantiate will be absolutely identical at inception. Surprise surprise, deterministic operations.

A Lesson in Deterministic Ops

Docker Tags are about as reliable and disposable as this guy down here.

Seems simple enough. You have probably already deployed hundreds of YAML’s or started endless counts of Docker containers.

docker run --name mynginx1 -P -d nginx:1.13.9

or

apiVersion: apps/v1
kind: Deployment
metadata:
  name: rss-site
spec:
  replicas: 1
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
        - name: front-end
          image: nginx:1.13.9
          ports:
            - containerPort: 80

But Tags are mutable and humans are prone to error. Not a good combination. Here, we’ll dig into why the use of tags can be dangerous and how to deploy your containers across a pipeline and across environments with determinism in mind.

Let’s say that you want to ensure that whether it’s today or 5 years from now, that specific deployment uses the very same image that you have defined. Any updates or newer versions of an image should be executed as a new deployment. The solution: digest

A digest takes the place of the tag when pulling an image. For example, to pull the above image by digest, run the following command:

docker run --name mynginx1 -P -d nginx@sha256:4771d09578c7c6a65299e110b3ee1c0a2592f5ea2618d23e4ffe7a4cab1ce5de

You can now make sure that the same image is always loaded at every deployment. It doesn’t matter if the TAG of the image has been changed or not. This solves the problem of repeatability.

Content Trust

However, there’s an additionally hidden danger. It is possible for an attacker to replace a server image with another one infected with malware.

Docker Content trust gives you the ability to verify both the integrity and the publisher of all the data received from a registry over any channel.

Prior to version 1.8, Docker didn’t have a way to verify the authenticity of a server image. But in v1.8, a new feature called Docker Content Trust was introduced to automatically sign and verify the signature of a publisher.

So, as soon as a server image is downloaded, it is cross-checked with the signature of the publisher to see if someone tampered with it in any way. This solves the problem of trust.

In addition, you should scan all images for known vulnerabilities.

11 - Kubernetes Antipatterns

This HowTo covers common Kubernetes antipatterns that we have seen over the past months.

Running as Root User

Whenever possible, do not run containers as root user. One could be tempted to say that Kubernetes pods and nodes are well separated. Host and containers running on it share the same kernel. If a container is compromised, the root user in the container has full control over the underlying node.

Watch the very good presentation by Liz Rice at the KubeCon 2018

Use RUN groupadd -r anygroup && useradd -r -g anygroup myuser to create a group and add a user to it. Use the USER command to switch to this user. Note that you may also consider to provide an explicit UID/GID if required.

For example:

ARG GF_UID="500"
ARG GF_GID="500"

# add group & user
RUN groupadd -r -g $GF_GID appgroup && \
   useradd appuser -r -u $GF_UID -g appgroup

USER appuser

Store Data or Logs in Containers

Containers are ideal for stateless applications and should be transient. This means that no data or logs should be stored in the container, as they are lost when the container is closed. Use persistence volumes instead to persist data outside of containers. Using an ELK stack is another good option for storing and processing logs.

Using Pod IP Addresses

Each pod is assigned an IP address. It is necessary for pods to communicate with each other to build an application, e.g. an application must communicate with a database. Existing pods are terminated and new pods are constantly started. If you would rely on the IP address of a pod or container, you would need to update the application configuration constantly. This makes the application fragile.

Create services instead. They provide a logical name that can be assigned independently of the varying number and IP addresses of containers. Services are the basic concept for load balancing within Kubernetes.

More Than One Process in a Container

A docker file provides a CMD and ENTRYPOINT to start the image. CMD is often used around a script that makes a configuration and then starts the container. Do not try to start multiple processes with this script. It is important to consider the separation of concerns when creating docker images. Running multiple processes in a single pod makes managing your containers, collecting logs and updating each process more difficult.

You can split the image into multiple containers and manage them independently - even in one pod. Bear in mind that Kubernetes only monitors the process with PID=1. If more than one process is started within a container, then these no longer fall under the control of Kubernetes.

Creating Images in a Running Container

A new image can be created with the docker commit command. This is useful if changes have been made to the container and you want to persist them for later error analysis. However, images created like this are not reproducible and completely worthless for a CI/CD environment. Furthermore, another developer cannot recognize which components the image contains. Instead, always make changes to the docker file, close existing containers and start a new container with the updated image.

Saving Passwords in a docker Image 💀

Do not save passwords in a Docker file! They are in plain text and are checked into a repository. That makes them completely vulnerable even if you are using a private repository like the Artifactory.

Always use Secrets or ConfigMaps to provision passwords or inject them by mounting a persistent volume.

Using the ’latest’ Tag

Starting an image with tomcat is tempting. If no tags are specified, a container is started with the tomcat:latest image. This image may no longer be up to date and refer to an older version instead. Running a production application requires complete control of the environment with exact versions of the image.

Make sure you always use a tag or even better the sha256 hash of the image e.g. tomcat@sha256:c34ce3c1fcc0c7431e1392cc3abd0dfe2192ffea1898d5250f199d3ac8d8720f.

Why Use the sha256 Hash?

Tags are not immutable and can be overwritten by a developer at any time. In this case you don’t have complete control over your image - which is bad.

Different Images per Environment

Don’t create different images for development, testing, staging and production environments. The image should be the source of truth and should only be created once and pushed to the repository. This image:tag should be used for different environments in the future.

Depend on Start Order of Pods

Applications often depend on containers being started in a certain order. For example, a database container must be up and running before an application can connect to it. The application should be resilient to such changes, as the db pod can be unreachable or restarted at any time. The application container should be able to handle such situations without terminating or crashing.

Additional Anti-Patterns and Patterns

In the community, vast experience has been collected to improve the stability and usability of Docker and Kubernetes.

Refer to Kubernetes Production Patterns for more information.

12 - Namespace Isolation

Overview

You can configure a NetworkPolicy to deny all the traffic from other namespaces while allowing all the traffic coming from the same namespace the pod was deployed into.

There are many reasons why you may chose to employ Kubernetes network policies:

• Isolate multi-tenant deployments
• Regulatory compliance
• Ensure containers assigned to different environments (e.g. dev/staging/prod) cannot interfere with each other

Kubernetes network policies are application centric compared to infrastructure/network centric standard firewalls. There are no explicit CIDRs or IP addresses used for matching source or destination IP’s. Network policies build up on labels and selectors which are key concepts of Kubernetes that are used to organize (for e.g all DB tier pods of an app) and select subsets of objects.

Example

We create two nginx HTTP-Servers in two namespaces and block all traffic between the two namespaces. E.g. you are unable to get content from namespace1 if you are sitting in namespace2.

Setup the Namespaces

# create two namespaces for test purpose
kubectl create ns customer1
kubectl create ns customer2

# create a standard HTTP web server
kubectl run nginx --image=nginx --replicas=1 --port=80 -n=customer1
kubectl run nginx --image=nginx --replicas=1 --port=80 -n=customer2

# expose the port 80 for external access
kubectl expose deployment nginx --port=80 --type=NodePort -n=customer1
kubectl expose deployment nginx --port=80 --type=NodePort -n=customer2

Test Without NP

Create a pod with curl preinstalled inside the namespace customer1:

# create a "bash" pod in one namespace
kubectl run -i --tty client --image=tutum/curl -n=customer1

Try to curl the exposed nginx server to get the default index.html page. Execute this in the bash prompt of the pod created above.

# get the index.html from the nginx of the namespace "customer1" => success
curl http://nginx.customer1
# get the index.html from the nginx of the namespace "customer2" => success
curl http://nginx.customer2

Both calls are done in a pod within the namespace customer1 and both nginx servers are always reachable, no matter in what namespace.

Test with NP

Install the NetworkPolicy from your shell:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: deny-from-other-namespaces
spec:
  podSelector:
    matchLabels:
  ingress:
  - from:
    - podSelector: {}

• it applies the policy to ALL pods in the named namespace as the spec.podSelector.matchLabels is empty and therefore selects all pods.
• it allows traffic from ALL pods in the named namespace, as spec.ingress.from.podSelector is empty and therefore selects all pods.

kubectl apply -f ./network-policy.yaml -n=customer1
kubectl apply -f ./network-policy.yaml -n=customer2

After this, curl http://nginx.customer2 shouldn’t work anymore if you are a service inside the namespace customer1 and vice versa

Related Links

You can get more information on how to configure the NetworkPolicies at:

• Calico WebSite
• Kubernetes NP Recipes

13 - Orchestration of Container Startup

Disclaimer

If an application depends on other services deployed separately, do not rely on a certain start sequence of containers. Instead, ensure that the application can cope with unavailability of the services it depends on.

Introduction

Kubernetes offers a feature called InitContainers to perform some tasks during a pod’s initialization. In this tutorial, we demonstrate how to use InitContainers in order to orchestrate a starting sequence of multiple containers. The tutorial uses the example app url-shortener, which consists of two components:

• postgresql database
• webapp which depends on the postgresql database and provides two endpoints: create a short url from a given location and redirect from a given short URL to the corresponding target location

This app represents the minimal example where an application relies on another service or database. In this example, if the application starts before the database is ready, the application will fail as shown below:

$ kubectl logs webapp-958cf5567-h247n
time="2018-06-12T11:02:42Z" level=info msg="Connecting to Postgres database using: host=`postgres:5432` dbname=`url_shortener_db` username=`user`\n"
time="2018-06-12T11:02:42Z" level=fatal msg="failed to start: failed to open connection to database: dial tcp: lookup postgres on 100.64.0.10:53: no such host\n"


$ kubectl get po -w
NAME                                READY     STATUS    RESTARTS   AGE
webapp-958cf5567-h247n   0/1       Pending   0         0s
webapp-958cf5567-h247n   0/1       Pending   0         0s
webapp-958cf5567-h247n   0/1       ContainerCreating   0         0s
webapp-958cf5567-h247n   0/1       ContainerCreating   0         1s
webapp-958cf5567-h247n   0/1       Error     0         2s
webapp-958cf5567-h247n   0/1       Error     1         3s
webapp-958cf5567-h247n   0/1       CrashLoopBackOff   1         4s
webapp-958cf5567-h247n   0/1       Error     2         18s
webapp-958cf5567-h247n   0/1       CrashLoopBackOff   2         29s
webapp-958cf5567-h247n   0/1       Error     3         43s
webapp-958cf5567-h247n   0/1       CrashLoopBackOff   3         56s

If the restartPolicy is set to Always (default) in the yaml file, the application will continue to restart the pod with an exponential back-off delay in case of failure.

Using InitContaniner

To avoid such a situation, InitContainers can be defined, which are executed prior to the application container. If one of the InitContainers fails, the application container won’t be triggered.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: webapp
spec:
  selector:
    matchLabels:
      app: webapp
  template:
    metadata:
      labels:
        app: webapp
    spec:
      initContainers:  # check if DB is ready, and only continue when true
      - name: check-db-ready
        image: postgres:9.6.5
        command: ['sh', '-c',  'until pg_isready -h postgres -p 5432;  do echo waiting for database; sleep 2; done;']
      containers:
      - image: xcoulon/go-url-shortener:0.1.0
        name: go-url-shortener
        env:
        - name: POSTGRES_HOST
          value: postgres
        - name: POSTGRES_PORT
          value: "5432"
        - name: POSTGRES_DATABASE
          value: url_shortener_db
        - name: POSTGRES_USER
          value: user
        - name: POSTGRES_PASSWORD
          value: mysecretpassword
        ports:
        - containerPort: 8080

In the above example, the InitContainers use the docker image postgres:9.6.5, which is different from the application container. This also brings the advantage of not having to include unnecessary tools (e.g. pg_isready) in the application container.

With introduction of InitContainers, in case the database is not available yet, the pod startup will look like similarly to:

$ kubectl get po -w
NAME                                READY     STATUS    RESTARTS   AGE
nginx-deployment-5cc79d6bfd-t9n8h   1/1       Running   0          5d
privileged-pod                      1/1       Running   0          4d
webapp-fdcb49cbc-4gs4n   0/1       Pending   0         0s
webapp-fdcb49cbc-4gs4n   0/1       Pending   0         0s
webapp-fdcb49cbc-4gs4n   0/1       Init:0/1   0         0s
webapp-fdcb49cbc-4gs4n   0/1       Init:0/1   0         1s


$ kubectl  logs webapp-fdcb49cbc-4gs4n
Error from server (BadRequest): container "go-url-shortener" in pod "webapp-fdcb49cbc-4gs4n" is waiting to start: PodInitializing

14 - Out-Dated HTML and JS Files Delivered

Problem

After updating your HTML and JavaScript sources in your web application, the Kubernetes cluster delivers outdated versions - why?

Overview

By default, Kubernetes service pods are not accessible from the external network, but only from other pods within the same Kubernetes cluster.

The Gardener cluster has a built-in configuration for HTTP load balancing called Ingress, defining rules for external connectivity to Kubernetes services. Users who want external access to their Kubernetes services create an ingress resource that defines rules, including the URI path, backing service name, and other information. The Ingress controller can then automatically program a frontend load balancer to enable Ingress configuration.

Example Ingress Configuration

apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
  name: vuejs-ingress
spec:
  rules:
  - host: test.ingress.<GARDENER-CLUSTER>.<GARDENER-PROJECT>.shoot.canary.k8s-hana.ondemand.com
    http:
      paths:
      - backend:
          serviceName: vuejs-svc
          servicePort: 8080

where:

• <GARDENER-CLUSTER>: The cluster name in the Gardener
• <GARDENER-PROJECT>: You project name in the Gardener

Diagnosing the Problem

The ingress controller we are using is NGINX. NGINX is a software load balancer, web server, and content cache built on top of open source NGINX.

NGINX caches the content as specified in the HTTP header. If the HTTP header is missing, it is assumed that the cache is forever and NGINX never updates the content in the stupidest case.

Solution

In general, you can avoid this pitfall with one of the solutions below:

• Use a cache buster + HTTP-Cache-Control (prefered)
• Use HTTP-Cache-Control with a lower retention period
• Disable the caching in the ingress (just for dev purposes)

Learning how to set the HTTP header or setup a cache buster is left to you, as an exercise for your web framework (e.g. Express/NodeJS, SpringBoot, …)

Here is an example on how to disable the cache control for your ingress, done with an annotation in your ingress YAML (during development).

---
apiVersion: networking.k8s.io/v1beta1
kind: Ingress
metadata:
  annotations:
    ingress.kubernetes.io/cache-enable: "false"
  name: vuejs-ingress
spec:
  rules:
  - host: test.ingress.<GARDENER-CLUSTER>.<GARDENER-PROJECT>.shoot.canary.k8s-hana.ondemand.com
    http:
      paths:
      - backend:
          serviceName: vuejs-svc
          servicePort: 8080

15 - Remove Committed Secrets in Github 💀

Overview

If you commit sensitive data, such as a kubeconfig.yaml or SSH key into a Git repository, you can remove it from the history. To entirely remove unwanted files from a repository’s history you can use the git filter-branch command.

The git filter-branch command rewrites your repository’s history, which changes the SHAs for existing commits that you alter and any dependent commits. Changed commit SHAs may affect open pull requests in your repository. Merging or closing all open pull requests before removing files from your repository is recommended.

Purging a File from Your Repository’s History

To illustrate how git filter-branch works, we’ll show you how to remove your file with sensitive data from the history of your repository and add it to .gitignore to ensure that it is not accidentally re-committed.

1. Navigate into the repository’s working directory:

cd YOUR-REPOSITORY

2. Run the following command, replacing PATH-TO-YOUR-FILE-WITH-SENSITIVE-DATA with the path to the file you want to remove, not just its filename.

These arguments will:

• Force Git to process, but not check out, the entire history of every branch and tag
• Remove the specified file, as well as any empty commits generated as a result
• Overwrite your existing tags

git filter-branch --force --index-filter \
'git rm --cached --ignore-unmatch PATH-TO-YOUR-FILE-WITH-SENSITIVE-DATA' \
--prune-empty --tag-name-filter cat -- --all

3. Add your file with sensitive data to .gitignore to ensure that you don’t accidentally commit it again:

 echo "YOUR-FILE-WITH-SENSITIVE-DATA" >> .gitignore

Double-check that you’ve removed everything you wanted to from your repository’s history, and that all of your branches are checked out. Once you’re happy with the state of your repository, continue to the next step.

4. Force-push your local changes to overwrite your GitHub repository, as well as all the branches you’ve pushed up:

git push origin --force --all

4. In order to remove the sensitive file from your tagged releases, you’ll also need to force-push against your Git tags:

git push origin --force --tags

Related Links

• Removing Sensitive Data from a Repository

16 - Using Prometheus and Grafana to Monitor K8s

Disclaimer

This post is meant to give a basic end-to-end description for deploying and using Prometheus and Grafana. Both applications offer a wide range of flexibility, which needs to be considered in case you have specific requirements. Such advanced details are not in the scope of this topic.

Introduction

Prometheus is an open-source systems monitoring and alerting toolkit for recording numeric time series. It fits both machine-centric monitoring as well as monitoring of highly dynamic service-oriented architectures. In a world of microservices, its support for multi-dimensional data collection and querying is a particular strength.

Prometheus is the second hosted project to graduate within CNCF.

The following characteristics make Prometheus a good match for monitoring Kubernetes clusters:

• Pull-based Monitoring Prometheus is a pull-based monitoring system, which means that the Prometheus server dynamically discovers and pulls metrics from your services running in Kubernetes.

• Labels Prometheus and Kubernetes share the same label (key-value) concept that can be used to select objects in the system.
  Labels are used to identify time series and sets of label matchers can be used in the query language (PromQL) to select the time series to be aggregated.

• Exporters
  There are many exporters available, which enable integration of databases or even other monitoring systems not already providing a way to export metrics to Prometheus. One prominent exporter is the so called node-exporter, which allows to monitor hardware and OS related metrics of Unix systems.

• Powerful Query Language The Prometheus query language PromQL lets the user select and aggregate time series data in real time. Results can either be shown as a graph, viewed as tabular data in the Prometheus expression browser, or consumed by external systems via the HTTP API.

Find query examples on Prometheus Query Examples.

One very popular open-source visualization tool not only for Prometheus is Grafana. Grafana is a metric analytics and visualization suite. It is popular for visualizing time series data for infrastructure and application analytics but many use it in other domains including industrial sensors, home automation, weather, and process control. For more information, see the Grafana Documentation.

Grafana accesses data via Data Sources. The continuously growing list of supported backends includes Prometheus.

Dashboards are created by combining panels, e.g., Graph and Dashlist.

In this example, we describe an End-To-End scenario including the deployment of Prometheus and a basic monitoring configuration as the one provided for Kubernetes clusters created by Gardener.

If you miss elements on the Prometheus web page when accessing it via its service URL https://<your K8s FQN>/api/v1/namespaces/<your-prometheus-namespace>/services/prometheus-prometheus-server:80/proxy, this is probably caused by a Prometheus issue - #1583. To workaround this issue, set up a port forward kubectl port-forward -n <your-prometheus-namespace> <prometheus-pod> 9090:9090 on your client and access the Prometheus UI from there with your locally installed web browser. This issue is not relevant in case you use the service type LoadBalancer.

Preparation

The deployment of Prometheus and Grafana is based on Helm charts.
Make sure to implement the Helm settings before deploying the Helm charts.

The Kubernetes clusters provided by Gardener use role based access control (RBAC). To authorize the Prometheus node-exporter to access hardware and OS relevant metrics of your cluster’s worker nodes, specific artifacts need to be deployed.

Bind the Prometheus service account to the garden.sapcloud.io:monitoring:prometheus cluster role by running the command kubectl apply -f crbinding.yaml.

Content of crbinding.yaml

apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  name: <your-prometheus-name>-server
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: garden.sapcloud.io:monitoring:prometheus
subjects:
- kind: ServiceAccount
  name: <your-prometheus-name>-server
  namespace: <your-prometheus-namespace>

Deployment of Prometheus and Grafana

Only minor changes are needed to deploy Prometheus and Grafana based on Helm charts.

Copy the following configuration into a file called values.yaml and deploy Prometheus: helm install <your-prometheus-name> --namespace <your-prometheus-namespace> stable/prometheus -f values.yaml

Typically, Prometheus and Grafana are deployed into the same namespace. There is no technical reason behind this, so feel free to choose different namespaces.

Content of values.yaml for Prometheus:

rbac:
  create: false # Already created in Preparation step
nodeExporter:
  enabled: false # The node-exporter is already deployed by default

server:
  global:
    scrape_interval: 30s
    scrape_timeout: 30s

serverFiles:
  prometheus.yml:
    rule_files:
      - /etc/config/rules
      - /etc/config/alerts      
    scrape_configs:
    - job_name: 'kube-kubelet'
      honor_labels: false
      scheme: https

      tls_config:
      # This is needed because the kubelets' certificates are not generated
      # for a specific pod IP
        insecure_skip_verify: true
      bearer_token_file: /var/run/secrets/kubernetes.io/serviceaccount/token

      kubernetes_sd_configs:
      - role: node
      relabel_configs:
      - target_label: __metrics_path__
        replacement: /metrics
      - source_labels: [__meta_kubernetes_node_address_InternalIP]
        target_label: instance
      - action: labelmap
        regex: __meta_kubernetes_node_label_(.+)

    - job_name: 'kube-kubelet-cadvisor'
      honor_labels: false
      scheme: https

      tls_config:
      # This is needed because the kubelets' certificates are not generated
      # for a specific pod IP
        insecure_skip_verify: true
      bearer_token_file: /var/run/secrets/kubernetes.io/serviceaccount/token

      kubernetes_sd_configs:
      - role: node
      relabel_configs:
      - target_label: __metrics_path__
        replacement: /metrics/cadvisor
      - source_labels: [__meta_kubernetes_node_address_InternalIP]
        target_label: instance
      - action: labelmap
        regex: __meta_kubernetes_node_label_(.+)

    # Example scrape config for probing services via the Blackbox Exporter.
    #
    # Relabelling allows to configure the actual service scrape endpoint using the following annotations:
    #
    # * `prometheus.io/probe`: Only probe services that have a value of `true`
    - job_name: 'kubernetes-services'
      metrics_path: /probe
      params:
        module: [http_2xx]
      kubernetes_sd_configs:
        - role: service
      relabel_configs:
        - source_labels: [__meta_kubernetes_service_annotation_prometheus_io_probe]
          action: keep
          regex: true
        - source_labels: [__address__]
          target_label: __param_target
        - target_label: __address__
          replacement: blackbox
        - source_labels: [__param_target]
          target_label: instance
        - action: labelmap
          regex: __meta_kubernetes_service_label_(.+)
        - source_labels: [__meta_kubernetes_namespace]
          target_label: kubernetes_namespace
        - source_labels: [__meta_kubernetes_service_name]
          target_label: kubernetes_name
    # Example scrape config for pods
    #
    # Relabelling allows to configure the actual service scrape endpoint using the following annotations:
    #
    # * `prometheus.io/scrape`: Only scrape pods that have a value of `true`
    # * `prometheus.io/path`: If the metrics path is not `/metrics` override this.
    # * `prometheus.io/port`: Scrape the pod on the indicated port instead of the default of `9102`.
    - job_name: 'kubernetes-pods'
      kubernetes_sd_configs:
        - role: pod
      relabel_configs:
        - source_labels: [__meta_kubernetes_pod_annotation_prometheus_io_scrape]
          action: keep
          regex: true
        - source_labels: [__meta_kubernetes_pod_annotation_prometheus_io_path]
          action: replace
          target_label: __metrics_path__
          regex: (.+)
        - source_labels: [__address__, __meta_kubernetes_pod_annotation_prometheus_io_port]
          action: replace
          regex: (.+):(?:\d+);(\d+)
          replacement: ${1}:${2}
          target_label: __address__
        - action: labelmap
          regex: __meta_kubernetes_pod_label_(.+)
        - source_labels: [__meta_kubernetes_namespace]
          action: replace
          target_label: kubernetes_namespace
        - source_labels: [__meta_kubernetes_pod_name]
          action: replace
          target_label: kubernetes_pod_name
    # Scrape config for service endpoints.
    #
    # The relabeling allows the actual service scrape endpoint to be configured
    # via the following annotations:
    #
    # * `prometheus.io/scrape`: Only scrape services that have a value of `true`
    # * `prometheus.io/scheme`: If the metrics endpoint is secured then you will need
    # to set this to `https` & most likely set the `tls_config` of the scrape config.
    # * `prometheus.io/path`: If the metrics path is not `/metrics` override this.
    # * `prometheus.io/port`: If the metrics are exposed on a different port to the
    # service then set this appropriately.
    - job_name: 'kubernetes-service-endpoints'
      kubernetes_sd_configs:
        - role: endpoints
      relabel_configs:
        - source_labels: [__meta_kubernetes_service_annotation_prometheus_io_scrape]
          action: keep
          regex: true
        - source_labels: [__meta_kubernetes_service_annotation_prometheus_io_scheme]
          action: replace
          target_label: __scheme__
          regex: (https?)
        - source_labels: [__meta_kubernetes_service_annotation_prometheus_io_path]
          action: replace
          target_label: __metrics_path__
          regex: (.+)
        - source_labels: [__address__, __meta_kubernetes_service_annotation_prometheus_io_port]
          action: replace
          target_label: __address__
          regex: (.+)(?::\d+);(\d+)
          replacement: $1:$2
        - action: labelmap
          regex: __meta_kubernetes_service_label_(.+)
        - source_labels: [__meta_kubernetes_namespace]
          action: replace
          target_label: kubernetes_namespace
        - source_labels: [__meta_kubernetes_service_name]
          action: replace
          target_label: kubernetes_name # Add your additional configuration here...

Next, deploy Grafana. Since the deployment in this post is based on the Helm default values, the settings below are set explicitly in case the default changed.

Deploy Grafana via helm install grafana --namespace <your-prometheus-namespace> stable/grafana -f values.yaml. Here, the same namespace is chosen for Prometheus and for Grafana.

Content of values.yaml for Grafana:

server:
  ingress:
    enabled: false
  service:
    type: ClusterIP

Check the running state of the pods on the Kubernetes Dashboard or by running kubectl get pods -n <your-prometheus-namespace>. In case of errors, check the log files of the pod(s) in question.

The text output of Helm after the deployment of Prometheus and Grafana contains very useful information, e.g., the user and password of the Grafana Admin user. The credentials are stored as secrets in the namespace <your-prometheus-namespace> and could be decoded via kubectl get secret --namespace <my-grafana-namespace> grafana -o jsonpath="{.data.admin-password}" | base64 --decode ; echo.

Basic Functional Tests

To access the web UI of both applications, use port forwarding of port 9090.

Setup port forwarding for port 9090:

kubectl port-forward -n <your-prometheus-namespace> <your-prometheus-server-pod> 9090:9090

Open http://localhost:9090 in your web browser. Select Graph from the top tab and enter the following expressing to show the overall CPU usage for a server (see Prometheus Query Examples):

100 * (1 - avg by(instance)(irate(node_cpu{mode='idle'}[5m])))

This should show some data in a graph.

To show the same data in Grafana setup port forwarding for port 3000 for the Grafana pod and open the Grafana Web UI by opening http://localhost:3000 in a browser. Enter the credentials of the admin user.

Next, you need to enter the server name of your Prometheus deployment. This name is shown directly after the installation via helm.

Run

helm status <your-prometheus-name>

to find this name. Below, this server name is referenced by <your-prometheus-server-name>.

First, you need to add your Prometheus server as data source:

1. Navigate to Dashboards → Data Sources
2. Choose Add data source
3. Enter:
   Name: <your-prometheus-datasource-name>
   Type: Prometheus
   URL: http://<your-prometheus-server-name>
   Access: proxy
4. Choose Save & Test

In case of failure, check the Prometheus URL in the Kubernetes Dashboard.

To add a Graph follow these steps:

1. In the left corner, select Dashboards → New to create a new dashboard
2. Select Graph to create a new graph
3. Next, select the Panel Title → Edit
4. Select your Prometheus Data Source in the drop down list
5. Enter the expression 100 * (1 - avg by(instance)(irate(node_cpu{mode='idle'}[5m]))) in the entry field A
6. Select the floppy disk symbol (Save) on top

Now you should have a very basic Prometheus and Grafana setup for your Kubernetes cluster.

As a next step you can implement monitoring for your applications by implementing the Prometheus client API.

Related Links

• Prometheus
• Prometheus Helm Chart
• Grafana
• Grafana Helm Chart