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README.md

Cluster Autoscaler Operator

The cluster-autoscaler-operator manages deployments of the OpenShift Cluster Autoscaler using the cluster-api provider.

Custom Resource Definitions

The operator manages the following custom resources:

  • ClusterAutoscaler: This is a singleton resource which controls the configuration of the cluster's autoscaler instance. The operator will only respond to the ClusterAutoscaler resource named "default" in the managed namespace, i.e. the value of the WATCH_NAMESPACE environment variable. (Example)

    The fields in the spec for ClusterAutoscaler resources correspond to command-line arguments to the cluster-autoscaler. The example linked above results in the following invocation:

      Command:
        cluster-autoscaler
      Args:
        --logtostderr
        --balance-similar-node-groups
        --cloud-provider=cluster-api
        --namespace=openshift-machine-api
        --expendable-pods-priority-cutoff=-10
        --max-nodes-total=24
        --cores-total=8:128
        --memory-total=4:256
        --gpu-total=nvidia.com/gpu:0:16
        --gpu-total=amd.com/gpu:0:4
        --scale-down-enabled=true
        --scale-down-delay-after-add=10s
        --scale-down-delay-after-delete=10s
        --scale-down-delay-after-failure=10s
        --ignore-daemonsets-utilization=false
        --skip-nodes-with-local-storage=true
    
  • MachineAutoscaler: This resource targets a node group and manages the annotations to enable and configure autoscaling for that group, e.g. the min and max size. Currently only MachineSet objects can be targeted. (Example)

Development

## Build, Test, & Run
$ make build
$ make test

$ export WATCH_NAMESPACE=openshift-machine-api
$ ./bin/cluster-autoscaler-operator -alsologtostderr

The Cluster Autoscaler Operator is designed to be deployed on OpenShift by the Cluster Version Operator, but it's possible to run it directly on any vanilla Kubernetes cluster that has the machine-api components available. To do so, apply the manifests in the install directory: kubectl apply -f ./install

This will create the openshift-machine-api namespace, register the custom resource definitions, configure RBAC policies, and create a deployment for the operator.

End-to-End Tests

You can run the e2e test suite with make test-e2e. These tests assume the presence of a cluster already running the operator, and that the KUBECONFIG environment variable points to a configuration granting admin rights on said cluster.

Validating Webhooks

By default the operator starts an HTTP server for webhooks and registers a ValidatingWebhookConfiguration with the API server for both the ClusterAutoscaler and MachineAutoscaler types. This can be disabled via the WEBHOOKS_ENABLED environment variable. At the moment, reconciliation of the webhook configuration is only performed once at startup after leader-election has succeeded.

If the webhook server is enabled, you must provide a TLS certificate and key as well as a CA certificate to the operator. The location of these is controlled by the WEBHOOKS_CERT_DIR environment variable, which defaults to: /etc/cluster-autoscaler-operator/tls

The files must be in the following locations:

  • ${WEBHOOKS_CERT_DIR}/tls.crt
  • ${WEBHOOKS_CERT_DIR}/tls.key
  • ${WEBHOOKS_CERT_DIR}/service-ca/ca-cert.pem

The default cluster-autoscaler-operator deployment on OpenShift will generate the TLS assets automatically with the help of the OpenShift service-ca-operator. This works by annotating the Service object associated with the operator, which causes the service-ca-operator to generate a TLS certificate and inject it into a Secret, which is then mounted into the operator pod. Additionally, the service-ca-operator injects its CA certificate into a ConfigMap, which is also mounted. The operator then uses the TLS certificate and key to secure the webhook HTTP server, and injects the CA certificate into the webhook configuration registered with the API server.

Updates to the TLS certificate and key are handled transparently. The controller-runtime library the operator is based on watches the files mounted in the pod for changes and updates HTTP server's TLS configuration. Updates to the CA certificate are not handled automatically, however a restart of the operator will load the new CA certificate and update the webhook configuration. This is not usually a problem in practice because CA certificates are generally long-lived and the webhook configuration is set to ignore communication failures as the validations are merely a convenience.