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  11 minute read  

Deploy a gardenlet Manually

Manually deploying a gardenlet is usually only required if the Kubernetes cluster to be registered as a seed cluster is managed via third-party tooling (i.e., the Kubernetes cluster is not a shoot cluster, so Deploy a gardenlet Automatically cannot be used). In this case, gardenlet needs to be deployed manually, meaning that its Helm chart must be installed.

lightbulb-on-outline

Tip

Once you’ve deployed a gardenlet manually, you can deploy new gardenlets automatically. The manually deployed gardenlet is then used as a template for the new gardenlets. For more information, see Deploy a gardenlet Automatically.

Prerequisites

Kubernetes Cluster that Should Be Registered as a Seed Cluster

  • Verify that the cluster has a supported Kubernetes version.

  • Determine the nodes, pods, and services CIDR of the cluster. You need to configure this information in the Seed configuration. Gardener uses this information to check that the shoot cluster isn’t created with overlapping CIDR ranges.

  • Every seed cluster needs an Ingress controller which distributes external requests to internal components like Plutono and Prometheus. For this, configure the following lines in your Seed resource:

    spec:
  dns:
    provider:
      type: aws-route53
      secretRef:
        name: ingress-secret
        namespace: garden
  ingress:
    domain: ingress.my-seed.example.com
    controller:
      kind: nginx
      providerConfig:
        <some-optional-provider-specific-config-for-the-ingressController>

Procedure Overview

  1. Prepare the garden cluster:
    1. Create a bootstrap token secret in the kube-system namespace of the garden cluster
    2. Create RBAC roles for the gardenlet to allow bootstrapping in the garden cluster
  2. Prepare the gardenlet Helm chart.
  3. Automatically register shoot cluster as a seed cluster.
  4. Deploy the gardenlet
  5. Check that the gardenlet is successfully deployed

Create a Bootstrap Token Secret in the kube-system Namespace of the Garden Cluster

The gardenlet needs to talk to the Gardener API server residing in the garden cluster.

Use gardenlet’s ability to request a signed certificate for the garden cluster by leveraging Kubernetes Certificate Signing Requests. The gardenlet performs a TLS bootstrapping process that is similar to the Kubelet TLS Bootstrapping. Make sure that the API server of the garden cluster has bootstrap token authentication enabled.

The client credentials required for the gardenlet’s TLS bootstrapping process need to be either token or certificate (OIDC isn’t supported) and have permissions to create a Certificate Signing Request (CSR). It’s recommended to use bootstrap tokens due to their desirable security properties (such as a limited token lifetime).

Therefore, first create a bootstrap token secret for the garden cluster:

apiVersion: v1
kind: Secret
metadata:
  # Name MUST be of form "bootstrap-token-<token id>"
  name: bootstrap-token-07401b
  namespace: kube-system

# Type MUST be 'bootstrap.kubernetes.io/token'
type: bootstrap.kubernetes.io/token
stringData:
  # Human readable description. Optional.
  description: "Token to be used by the gardenlet for Seed `sweet-seed`."

  # Token ID and secret. Required.
  token-id: 07401b # 6 characters
  token-secret: f395accd246ae52d # 16 characters

  # Expiration. Optional.
  # expiration: 2017-03-10T03:22:11Z

  # Allowed usages.
  usage-bootstrap-authentication: "true"
  usage-bootstrap-signing: "true"

When you later prepare the gardenlet Helm chart, a kubeconfig based on this token is shared with the gardenlet upon deployment.

Prepare the gardenlet Helm Chart

This section only describes the minimal configuration, using the global configuration values of the gardenlet Helm chart. For an overview over all values, see the configuration values. We refer to the global configuration values as gardenlet configuration in the following procedure.

  1. Create a gardenlet configuration gardenlet-values.yaml based on this template.

  2. Create a bootstrap kubeconfig based on the bootstrap token created in the garden cluster.

    Replace the <bootstrap-token> with token-id.token-secret (from our previous example: 07401b.f395accd246ae52d) from the bootstrap token secret.

    apiVersion: v1
kind: Config
current-context: gardenlet-bootstrap@default
clusters:
- cluster:
    certificate-authority-data: <ca-of-garden-cluster>
    server: https://<endpoint-of-garden-cluster>
  name: default
contexts:
- context:
    cluster: default
    user: gardenlet-bootstrap
  name: gardenlet-bootstrap@default
users:
- name: gardenlet-bootstrap
  user:
    token: <bootstrap-token>

  3. In the gardenClientConnection.bootstrapKubeconfig section of your gardenlet configuration, provide the bootstrap kubeconfig together with a name and namespace to the gardenlet Helm chart.

    gardenClientConnection:
  bootstrapKubeconfig:
    name: gardenlet-kubeconfig-bootstrap
    namespace: garden
    kubeconfig: |
      <bootstrap-kubeconfig>  # will be base64 encoded by helm

    The bootstrap kubeconfig is stored in the specified secret.

  4. In the gardenClientConnection.kubeconfigSecret section of your gardenlet configuration, define a name and a namespace where the gardenlet stores the real kubeconfig that it creates during the bootstrap process. If the secret doesn’t exist, the gardenlet creates it for you.

    gardenClientConnection:
  kubeconfigSecret:
    name: gardenlet-kubeconfig
    namespace: garden

Updating the Garden Cluster CA

The kubeconfig created by the gardenlet in step 4 will not be recreated as long as it exists, even if a new bootstrap kubeconfig is provided. To enable rotation of the garden cluster CA certificate, a new bundle can be provided via the gardenClientConnection.gardenClusterCACert field. If the provided bundle differs from the one currently in the gardenlet’s kubeconfig secret then it will be updated. To remove the CA completely (e.g. when switching to a publicly trusted endpoint), this field can be set to either none or null.

Prepare Seed Specification

When gardenlet starts, it tries to register a Seed resource in the garden cluster based on the specification provided in seedConfig in its configuration.

This procedure doesn’t describe all the possible configurations for the Seed resource. For more information, see:

  1. Supply the Seed resource in the seedConfig section of your gardenlet configuration gardenlet-values.yaml.

  2. Add the seedConfig to your gardenlet configuration gardenlet-values.yaml. The field seedConfig.spec.provider.type specifies the infrastructure provider type (for example, aws) of the seed cluster. For all supported infrastructure providers, see Known Extension Implementations.

    # ...
seedConfig:
  metadata:
    name: sweet-seed
    labels:
      environment: evaluation
    annotations:
      custom.gardener.cloud/option: special
  spec:
    dns:
      provider:
        type: <provider>
        secretRef:
          name: ingress-secret
          namespace: garden
    ingress: # see prerequisites
      domain: ingress.dev.my-seed.example.com
      controller:
        kind: nginx
    networks: # see prerequisites
      nodes: 10.240.0.0/16
      pods: 100.244.0.0/16
      services: 100.32.0.0/13
      shootDefaults: # optional: non-overlapping default CIDRs for shoot clusters of that Seed
        pods: 100.96.0.0/11
        services: 100.64.0.0/13
    provider:
      region: eu-west-1
      type: <provider>

Apart from the seed’s name, seedConfig.metadata can optionally contain labels and annotations. gardenlet will set the labels of the registered Seed object to the labels given in the seedConfig plus gardener.cloud/role=seed. Any custom labels on the Seed object will be removed on the next restart of gardenlet. If a label is removed from the seedConfig it is removed from the Seed object as well. In contrast to labels, annotations in the seedConfig are added to existing annotations on the Seed object. Thus, custom annotations that are added to the Seed object during runtime are not removed by gardenlet on restarts. Furthermore, if an annotation is removed from the seedConfig, gardenlet does not remove it from the Seed object.

Optional: Enable HA Mode

You may consider running gardenlet with multiple replicas, especially if the seed cluster is configured to host HA shoot control planes. Therefore, the following Helm chart values define the degree of high availability you want to achieve for the gardenlet deployment.

replicaCount: 2 # or more if a higher failure tolerance is required.
failureToleranceType: zone # One of `zone` or `node` - defines how replicas are spread.

Optional: Enable Backup and Restore

The seed cluster can be set up with backup and restore for the main etcds of shoot clusters.

Gardener uses etcd-backup-restore that integrates with different storage providers to store the shoot cluster’s main etcd backups. Make sure to obtain client credentials that have sufficient permissions with the chosen storage provider.

Create a secret in the garden cluster with client credentials for the storage provider. The format of the secret is cloud provider specific and can be found in the repository of the respective Gardener extension. For example, the secret for AWS S3 can be found in the AWS provider extension (30-etcd-backup-secret.yaml).

apiVersion: v1
kind: Secret
metadata:
  name: sweet-seed-backup
  namespace: garden
type: Opaque
data:
  # client credentials format is provider specific

Configure the Seed resource in the seedConfig section of your gardenlet configuration to use backup and restore:

# ...
seedConfig:
  metadata:
    name: sweet-seed
  spec:
    backup:
      provider: <provider>
      secretRef:
        name: sweet-seed-backup
        namespace: garden

Optional: Enable Self-Upgrades

In order to take off the continuous task of deploying gardenlet’s Helm chart in case you want to upgrade its version, it supports self-upgrades. The way this works is that it pulls information (its configuration and deployment values) from a seedmanagement.gardener.cloud/v1alpha1.Gardenlet resource in the garden cluster. This resource must be in the garden namespace and must have the same name as the Seed the gardenlet is responsible for. For more information, see this section.

In order to make gardenlet automatically create a corresponding seedmanagement.gardener.cloud/v1alpha1.Gardenlet resource, you must provide

selfUpgrade:
  deployment:
    helm:
      ociRepository:
        ref: <url-to-oci-repository-containing-gardenlet-helm-chart>

in your gardenlet-values.yaml file. Please replace the ref placeholder with the URL to the OCI repository containing the gardenlet Helm chart you are installing.

information-outline

If you don’t configure this selfUpgrade section in the initial deployment, you can also do it later, or you directly create the corresponding seedmanagement.gardener.cloud/v1alpha1.Gardenlet resource in the garden cluster.

Deploy the gardenlet

The gardenlet-values.yaml looks something like this (with backup for shoot clusters enabled):

# <default config>
# ...
config:
  gardenClientConnection:
    # ...
    bootstrapKubeconfig:
      name: gardenlet-bootstrap-kubeconfig
      namespace: garden
      kubeconfig: |
        apiVersion: v1
        clusters:
        - cluster:
            certificate-authority-data: <dummy>
            server: <my-garden-cluster-endpoint>
          name: my-kubernetes-cluster
        # ...        

    kubeconfigSecret:
      name: gardenlet-kubeconfig
      namespace: garden
  # ...
  # <default config>
  # ...
  seedConfig:
    metadata:
      name: sweet-seed
    spec:
      dns:
        provider:
          type: <provider>
          secretRef:
            name: ingress-secret
            namespace: garden
      ingress: # see prerequisites
        domain: ingress.dev.my-seed.example.com
        controller:
          kind: nginx
      networks:
        nodes: 10.240.0.0/16
        pods: 100.244.0.0/16
        services: 100.32.0.0/13
        shootDefaults:
          pods: 100.96.0.0/11
          services: 100.64.0.0/13
      provider:
        region: eu-west-1
        type: <provider>
      backup:
        provider: <provider>
        secretRef:
          name: sweet-seed-backup
          namespace: garden

Deploy the gardenlet Helm chart to the Kubernetes cluster:

helm install gardenlet charts/gardener/gardenlet \
  --namespace garden \
  -f gardenlet-values.yaml \
  --wait

This Helm chart creates:

  • A service account gardenlet that the gardenlet can use to talk to the Seed API server.
  • RBAC roles for the service account (full admin rights at the moment).
  • The secret (garden/gardenlet-bootstrap-kubeconfig) containing the bootstrap kubeconfig.
  • The gardenlet deployment in the garden namespace.

Check that the gardenlet Is Successfully Deployed

  1. Check that the gardenlets certificate bootstrap was successful.

    Check if the secret gardenlet-kubeconfig in the namespace garden in the seed cluster is created and contains a kubeconfig with a valid certificate.

    1. Get the kubeconfig from the created secret.

      $ kubectl -n garden get secret gardenlet-kubeconfig -o json | jq -r .data.kubeconfig | base64 -d

    2. Test against the garden cluster and verify it’s working.

    3. Extract the client-certificate-data from the user gardenlet.

    4. View the certificate:

      $ openssl x509 -in ./gardenlet-cert -noout -text

  2. Check that the bootstrap secret gardenlet-bootstrap-kubeconfig has been deleted from the seed cluster in namespace garden.

  3. Check that the seed cluster is registered and READY in the garden cluster.

    Check that the seed cluster sweet-seed exists and all conditions indicate that it’s available. If so, the Gardenlet is sending regular heartbeats and the seed bootstrapping was successful.

    Check that the conditions on the Seed resource look similar to the following:

    $ kubectl get seed sweet-seed -o json | jq .status.conditions
[
  {
    "lastTransitionTime": "2020-07-17T09:17:29Z",
    "lastUpdateTime": "2020-07-17T09:17:29Z",
    "message": "Gardenlet is posting ready status.",
    "reason": "GardenletReady",
    "status": "True",
    "type": "GardenletReady"
  },
  {
    "lastTransitionTime": "2020-07-17T09:17:49Z",
    "lastUpdateTime": "2020-07-17T09:53:17Z",
    "message": "Backup Buckets are available.",
    "reason": "BackupBucketsAvailable",
    "status": "True",
    "type": "BackupBucketsReady"
  }
]

Self Upgrades

In order to keep your gardenlets in such “unmanaged seeds” up-to-date (i.e., in seeds which are no shoot clusters), its Helm chart must be regularly deployed. This requires network connectivity to such clusters which can be challenging if they reside behind a firewall or in restricted environments. It is much simpler if gardenlet could keep itself up-to-date, based on configuration read from the garden cluster. This approach greatly reduces operational complexity.

gardenlet runs a controller which watches for seedmanagement.gardener.cloud/v1alpha1.Gardenlet resources in the garden cluster in the garden namespace having the same name as the Seed the gardenlet is responsible for. Such resources contain its component configuration and deployment values. Most notably, a URL to an OCI repository containing gardenlet’s Helm chart is included.

An example Gardenlet resource looks like this:

apiVersion: seedmanagement.gardener.cloud/v1alpha1
kind: Gardenlet
metadata:
  name: local
  namespace: garden
spec:
  deployment:
    replicaCount: 1
    revisionHistoryLimit: 2
    helm:
      ociRepository:
        ref: <url-to-gardenlet-chart-repository>:v1.97.0
  config:
    apiVersion: gardenlet.config.gardener.cloud/v1alpha1
    kind: GardenletConfiguration
    gardenClientConnection:
      kubeconfigSecret:
        name: gardenlet-kubeconfig
        namespace: garden
    controllers:
      shoot:
        reconcileInMaintenanceOnly: true
        respectSyncPeriodOverwrite: true
      shootState:
        concurrentSyncs: 0
    featureGates:
      DefaultSeccompProfile: true
      ShootManagedIssuer: true
    etcdConfig:
      featureGates:
        UseEtcdWrapper: true
    logging:
      enabled: true
      vali:
        enabled: true
      shootNodeLogging:
        shootPurposes:
        - infrastructure
        - production
        - development
        - evaluation
    seedConfig:
      apiVersion: core.gardener.cloud/v1beta1
      kind: Seed
      metadata:
        labels:
          base: kind
      spec:
        backup:
          provider: local
          region: local
          secretRef:
            name: backup-local
            namespace: garden
        dns:
          provider:
            secretRef:
              name: internal-domain-internal-local-gardener-cloud
              namespace: garden
            type: local
        ingress:
          controller:
            kind: nginx
          domain: ingress.local.seed.local.gardener.cloud
        networks:
          nodes: 172.18.0.0/16
          pods: 10.1.0.0/16
          services: 10.2.0.0/16
          shootDefaults:
            pods: 10.3.0.0/16
            services: 10.4.0.0/16
        provider:
          region: local
          type: local
          zones:
          - "0"
        settings:
          excessCapacityReservation:
            enabled: false
          scheduling:
            visible: true
          verticalPodAutoscaler:
            enabled: true

On reconciliation, gardenlet downloads the Helm chart, renders it with the provided values, and then applies it to its own cluster. Hence, in order to keep a gardenlet up-to-date, it is enough to update the tag/digest of the OCI repository ref for the Helm chart:

spec:
  deployment:
    helm:
      ociRepository:
        ref: <url-to-gardenlet-chart-repository>:v1.97.0

This way, network connectivity to the cluster in which gardenlet runs is not required at all (at least for deployment purposes).

When you delete this resource, nothing happens: gardenlet remains running with the configuration as before. However, self-upgrades are obviously not possible anymore. In order to upgrade it, you have to either recreate the Gardenlet object, or redeploy the Helm chart.