7 minute read  

Logging Stack

Motivation

Kubernetes uses the underlying container runtime logging, which does not persist logs for stopped and destroyed containers. This makes it difficult to investigate issues in the very common case of not running containers. Gardener provides a solution to this problem for the managed cluster components by introducing its own logging stack.

Components

• A Fluent-bit daemonset which works like a log collector and custom Golang plugin which spreads log messages to their Vali instances.
• One Vali Statefulset in the garden namespace which contains logs for the seed cluster and one per shoot namespace which contains logs for shoot’s controlplane.
• One Plutono Deployment in garden namespace and two Deployments per shoot namespace (one exposed to the end users and one for the operators). Plutono is the UI component used in the logging stack.

Container Logs Rotation and Retention

Container log rotation in Kubernetes describes a subtile but important implementation detail depending on the type of the used high-level container runtime. When the used container runtime is not CRI compliant (such as dockershim), then the kubelet does not provide any rotation or retention implementations, hence leaving those aspects to the downstream components. When the used container runtime is CRI compliant (such as containerd), then the kubelet provides the necessary implementation with two configuration options:

• ContainerLogMaxSize for rotation
• ContainerLogMaxFiles for retention

Docker Container Runtime

In this case, the log rotation and retention is implemented by a logrotate service provisioned by Gardener, which rotates logs once 100M size is reached. Logs are compressed on daily basis and retained for a maximum period of 14d.

ContainerD Runtime

In this case, it is possible to configure the containerLogMaxSize and containerLogMaxFiles fields in the Shoot specification. Both fields are optional and if nothing is specified, then the kubelet rotates on the same size 100M as in the docker container runtime. Those fields are part of provider’s workers definition. Here is an example:

spec:
  provider:
    workers:
      - cri:
          name: containerd
        kubernetes:
          kubelet:
            # accepted values are of resource.Quantity
            containerLogMaxSize: 150Mi
            containerLogMaxFiles: 10

The values of the containerLogMaxSize and containerLogMaxFiles fields need to be considered with care since container log files claim disk space from the host. On the opposite side, log rotations on too small sizes may result in frequent rotations which can be missed by other components (log shippers) observing these rotations.

In the majority of the cases, the defaults should do just fine. Custom configuration might be of use under rare conditions.

Extension of the Logging Stack

The logging stack is extended to scrape logs from the systemd services of each shoots’ nodes and from all Gardener components in the shoot kube-system namespace. These logs are exposed only to the Gardener operators.

Also, in the shoot control plane an event-logger pod is deployed, which scrapes events from the shoot kube-system namespace and shoot control-plane namespace in the seed. The event-logger logs the events to the standard output. Then the fluent-bit gets these events as container logs and sends them to the Vali in the shoot control plane (similar to how it works for any other control plane component).

How to Access the Logs

The logs are accessible via Plutono. To access them:

1. Authenticate via basic auth to gain access to Plutono. The Plutono URL can be found in the Logging and Monitoring section of a cluster in the Gardener Dashboard alongside the credentials. The secret containing the credentials is stored in the project namespace following the naming pattern <shoot-name>.monitoring. For Gardener operators, the credentials are also stored in the control-plane (shoot--<project-name>--<shoot-name>) namespace in the observability-ingress-users-<hash> secret in the seed.

2. Plutono contains several dashboards that aim to facilitate the work of operators and users. From the Explore tab, users and operators have unlimited abilities to extract and manipulate logs.

Note: Gardener Operators are people part of the Gardener team with operator permissions, not operators of the end-user cluster!

How to Use the Explore Tab

If you click on the Log browser > button, you will see all of the available labels. Clicking on the label, you can see all of its available values for the given period of time you have specified. If you are searching for logs for the past one hour, do not expect to see labels or values for which there were no logs for that period of time. By clicking on a value, Plutono automatically eliminates all other labels and/or values with which no valid log stream can be made. After choosing the right labels and their values, click on the Show logs button. This will build Log query and execute it. This approach is convenient when you don’t know the labels names or they values.

Once you feel comfortable, you can start to use the LogQL language to search for logs. Next to the Log browser > button is the place where you can type log queries.

Examples:

1. If you want to get logs for calico-node-<hash> pod in the cluster kube-system: The name of the node on which calico-node was running is known, but not the hash suffix of the calico-node pod. Also we want to search for errors in the logs.

   {pod_name=~"calico-node-.+", nodename="ip-10-222-31-182.eu-central-1.compute.internal"} |~ "error"

   Here, you will get as much help as possible from the Plutono by giving you suggestions and auto-completion.

2. If you want to get the logs from kubelet systemd service of a given node and search for a pod name in the logs:

   {unit="kubelet.service", nodename="ip-10-222-31-182.eu-central-1.compute.internal"} |~ "pod name"

Note: Under unit label there is only the docker, containerd, kubelet and kernel logs.

3. If you want to get the logs from cloud-config-downloader systemd service of a given node and search for a string in the logs:

   {job="systemd-combine-journal",nodename="ip-10-222-31-182.eu-central-1.compute.internal"} | unpack | unit="cloud-config-downloader.service" |~ "last execution was"

Note: {job="systemd-combine-journal",nodename="<node name>"} stream pack all logs from systemd services except docker, containerd, kubelet, and kernel. To filter those log by unit, you have to unpack them first.

4. Retrieving events:

• If you want to get the events from the shoot kube-system namespace generated by kubelet and related to the node-problem-detector:

  {job="event-logging"} | unpack | origin_extracted="shoot",source="kubelet",object=~".*node-problem-detector.*"

• If you want to get the events generated by MCM in the shoot control plane in the seed:

  {job="event-logging"} | unpack | origin_extracted="seed",source=~".*machine-controller-manager.*"

  Note: In order to group events by origin, one has to specify origin_extracted because the origin label is reserved for all of the logs from the seed and the event-logger resides in the seed, so all of its logs are coming as they are only from the seed. The actual origin is embedded in the unpacked event. When unpacked, the embedded origin becomes origin_extracted.

Expose Logs for Component to User Plutono

Exposing logs for a new component to the User’s Plutono is described in the How to Expose Logs to the Users section.

Configuration

Fluent-bit

The Fluent-bit configurations can be found on pkg/component/logging/fluentoperator/customresources There are six different specifications:

• FluentBit: Defines the fluent-bit DaemonSet specifications
• ClusterFluentBitConfig: Defines the labelselectors of the resources which fluent-bit will match
• ClusterInput: Defines the location of the input stream of the logs
• ClusterOutput: Defines the location of the output source (Vali for example)
• ClusterFilter: Defines filters which match specific keys
• ClusterParser: Defines parsers which are used by the filters

Vali

The Vali configurations can be found on charts/seed-bootstrap/charts/vali/templates/vali-configmap.yaml

The main specifications there are:

• Index configuration: Currently the following one is used:

    schema_config:
      configs:
      - from: 2018-04-15
        store: boltdb
        object_store: filesystem
        schema: v11
        index:
          prefix: index_
          period: 24h

• from: Is the date from which logs collection is started. Using a date in the past is okay.
• store: The DB used for storing the index.
• object_store: Where the data is stored.
• schema: Schema version which should be used (v11 is currently recommended).
• index.prefix: The prefix for the index.
• index.period: The period for updating the indices.

Adding a new index happens with new config block definition. The from field should start from the current day + previous index.period and should not overlap with the current index. The prefix also should be different.

    schema_config:
      configs:
      - from: 2018-04-15
        store: boltdb
        object_store: filesystem
        schema: v11
        index:
          prefix: index_
          period: 24h
      - from: 2020-06-18
        store: boltdb
        object_store: filesystem
        schema: v11
        index:
          prefix: index_new_
          period: 24h

• chunk_store_config Configuration

    chunk_store_config:
      max_look_back_period: 336h

chunk_store_config.max_look_back_period should be the same as the retention_period

• table_manager Configuration

    table_manager:
      retention_deletes_enabled: true
      retention_period: 336h

table_manager.retention_period is the living time for each log message. Vali will keep messages for (table_manager.retention_period - index.period) time due to specification in the Vali implementation.

Plutono

The Plutono configurations can be found on charts/seed-bootstrap/charts/templates/plutono/plutono-datasources-configmap.yaml and charts/seed-monitoring/charts/plutono/tempates/plutono-datasources-configmap.yaml

This is the Vali configuration that Plutono uses:

    - name: vali
      type: vali
      access: proxy
      url: http://logging.{{ .Release.Namespace }}.svc:3100
      jsonData:
        maxLines: 5000

• name: Is the name of the datasource.
• type: Is the type of the datasource.
• access: Should be set to proxy.
• url: Vali’s url
• svc: Vali’s port
• jsonData.maxLines: The limit of the log messages which Plutono will show to the users.

Decrease this value if the browser works slowly!