Kubernetes API Server Operator
The Kubernetes API Server operator manages and updates the Kubernetes API server deployed on top of OpenShift. The operator is based on OpenShift library-go framework and it is installed via Cluster Version Operator (CVO).
It contains the following components:
- Operator
- Bootstrap manifest renderer
- Installer based on static pods
- Configuration observer
By default, the operator exposes Prometheus metrics via metrics
service.
The metrics are collected from following components:
- Kubernetes API Server Operator
Configuration
The configuration observer component is responsible for reacting on external configuration changes. For example, this allows external components (registry, etcd, etc..) to interact with the Kubernetes API server configuration (KubeAPIServerConfig custom resource).
Currently changes in following external components are being observed:
host-etcd
endpoints in kube-system namespace- The observed endpoint addresses are used to configure the
storageConfig.urls
in Kubernetes API server configuration.
- The observed endpoint addresses are used to configure the
cluster
image.config.openshift.io custom resource- The observed CR resource is used to configure the
imagePolicyConfig.internalRegistryHostname
in Kubernetes API server configuration
- The observed CR resource is used to configure the
cluster-config-v1
configmap in kube-system namespace- The observed configmap
install-config
is decoded and thenetworking.podCIDR
andnetworking.serviceCIDR
is extracted and used as input foradmissionPluginConfig.openshift.io/RestrictedEndpointsAdmission.configuration.restrictedCIDRs
andservicesSubnet
- The observed configmap
The configuration for the Kubernetes API server is the result of merging:
- a default config
- observed config (compare observed values above)
spec.spec.unsupportedConfigOverrides
from thekubeapiserveroperatorconfig
.
All of these are sparse configurations, i.e. unvalidated json snippets which are merged in order to form a valid configuration at the end.
Debugging
Operator also expose events that can help debugging issues. To get operator events, run following command:
$ oc get events -n openshift-cluster-kube-apiserver-operator
This operator is configured via KubeAPIServer
custom resource:
$ oc describe kubeapiserver
apiVersion: operator.openshift.io/v1
kind: KubeAPIServer
metadata:
name: cluster
spec:
managementState: Managed
The current operator status is reported using the ClusterOperator
resource. To get the current status you can run follow command:
$ oc get clusteroperator/kube-apiserver
Developing and debugging the operator
In the running cluster cluster-version-operator is responsible for maintaining functioning and non-altered elements. In that case to be able to use custom operator image one has to perform one of these operations:
- Set your operator in umanaged state, see here for details, in short:
oc patch clusterversion/version --type='merge' -p "$(cat <<- EOF
spec:
overrides:
- group: apps
kind: Deployment
name: kube-apiserver-operator
namespace: openshift-kube-apiserver-operator
unmanaged: true
EOF
)"
- Scale down cluster-version-operator:
oc scale --replicas=0 deploy/cluster-version-operator -n openshift-cluster-version
IMPORTANT: This approach disables cluster-version-operator completely, whereas the previous patch only tells it to not manage a kube-apiserver-operator!
After doing this you can now change the image of the operator to the desired one:
oc patch pod/kube-apiserver-operator-<rand_digits> -n openshift-kube-apiserver-operator -p '{"spec":{"containers":[{"name":"kube-apiserver-operator","image":"<user>/cluster-kube-apiserver-operator"}]}}'
Developing and debugging the bootkube bootstrap phase
The operator image version used by the https://github.com/openshift/installer/blob/master/pkg/asset/ignition/bootstrap/bootstrap.go#L178 bootstrap phase can be overridden by creating a custom origin-release image pointing to the developer's operator :latest
image:
$ IMAGE_ORG=sttts make images
$ docker push sttts/origin-cluster-kube-apiserver-operator
$ cd ../cluster-kube-apiserver-operator
$ oc adm release new --from-release=registry.svc.ci.openshift.org/openshift/origin-release:v4.0 cluster-kube-apiserver-operator=docker.io/sttts/origin-cluster-kube-apiserver-operator:latest --to-image=sttts/origin-release:latest
$ cd ../installer
$ OPENSHIFT_INSTALL_RELEASE_IMAGE_OVERRIDE=docker.io/sttts/origin-release:latest bin/openshift-install cluster ...
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