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Migrate from in-tree cloud provider to openstack-cloud-controller-manager and enable CSIMigration

This guide walks you through the process of migrating from using the Kubernetes in-tree cloud provider (specified by using --cloud-provider=openstack on kube-controller-manager) to use the cloud-controller-manager (CCM) for OpenStack. This document tries to give an example for using multiple steps in order to get the migration fully done. We expect users to want to migrate to cloud-provider-openstack but stay with the in-tree cinder-volume-provisioner up until CSIMigration has become GA.

A little bit of background on CSI and CSIMigration. These days, storage providers should implement the Container Storage Interface to provide storage for Kubernetes clusters (but not limited to Kubernetes). cloud-provider-openstack also provides Cinder CSI Plugin to serve exact this purpose. This plugin can be installed and used alongside in-tree cloud-provider, because it requires its own StorageClass. What this means is: All volumes, created by the in-tree volume APIs will be handled by the old in-tree-provisioner one. Everything provisioned by Cinder CSI Plugin, will be handled by cinder-csi-plugin.

Sometimes it can be hard to migrate an entire cluster to use the new StorageClass. This is where CSIMigration comes into play (see CSIMigration design proposal). With this enabled, calls to the in-tree volume APIs will call out to the CSI plugins.

Before you begin

Note: This guide works on a cluster created by kubeadm.

Example kubeadm.yaml:

apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
kubernetesVersion: 1.17.0-beta.1
networking:
  podSubnet: 10.96.0.0/16
  serviceSubnet: 10.97.0.0/16
controllerManager:
  extraArgs:
    cloud-provider: openstack
    cloud-config: /etc/kubernetes/cloud.conf
  extraVolumes:
  - name: cloud
    hostPath: /etc/kubernetes/cloud.conf
    mountPath: /etc/kubernetes/cloud.conf
    readOnly: true
---
apiVersion: kubeadm.k8s.io/v1beta2
kind: InitConfiguration
localAPIEndpoint:
  bindPort: 6443
nodeRegistration:
  kubeletExtraArgs:
    cloud-provider: openstack
    cloud-config: /etc/kubernetes/cloud.conf

Migrate to openstack-cloud-controller-manager

Remember... In the first step, we want to keep the in-tree volume API, but for all of the rest, we want to use openstack-cloud-controller-manager. So we can't just remove the --cloud-provider flag from kube-controller-manager. In fact, we must disable all cloud related controllers. Create the file kubeadm-disable-controllers.yaml:

apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
kubernetesVersion: 1.17.0-beta.1
networking:
  podSubnet: 10.96.0.0/16
  serviceSubnet: 10.97.0.0/16
controllerManager:
  extraArgs:
    cloud-provider: openstack
    cloud-config: /etc/kubernetes/cloud.conf
    controllers: '*,bootstrapsigner,tokencleaner,-cloud-node-lifecycle,-route,-service'
  extraVolumes:
  - name: cloud
    hostPath: /etc/kubernetes/cloud.conf
    mountPath: /etc/kubernetes/cloud.conf
    readOnly: true

And create new manifests for kube-controller-manager:

kubeadm init --config kubeadm-disable-controllers.yaml phase control-plane controller-manager

To verify, check the logs of kube-controller-manager for the following lines.

W1117 19:59:34.094182       1 controllermanager.go:513] "service" is disabled
W1117 19:59:34.094187       1 controllermanager.go:513] "route" is disabled
W1117 19:59:44.988353       1 controllermanager.go:513] "cloud-node-lifecycle" is disabled

You can now deploy openstack-cloud-controller-manager using RBAC and the CCM manifest. But disable the controller cloud-node by adding the argument --controllers=*,-cloud-node. This will be done by the kubelets up until the entire migration is done. Note: You must create a secret cloud-config with a valid cloud.conf for the CCM. E.g.

kubectl -n kube-system create secret generic cloud-config --from-file=cloud.conf=/etc/kubernetes/cloud.conf

Note: Because you still want to use the in-tree volume API, you must keep the arguments on the kubelets untouched (meaning, stick with --cloud-provider=openstack and --cloud-config=/etc/kubernetes/cloud.conf) for now.

At this point, the cluster should work as before. LoadBalancers can be created and StatefulSets create and use persistent volumes. Note: The logs of openstack-cloud-controller-manager in namespace kube-system reveal, that this now takes care of creating LoadBalancers. All further management of existing LoadBalancers is taken over by openstack-cloud-controller-manager as well. There is no need to recreate any LoadBalancer.

At this point, you should also deploy Cinder CSI Plugin. As mentioned above, this can be deployed alogside the in-tree provider. We would recommend to create a separate StorageClass for Cinder CSI Plugin, and make it the default. (refer example)

Enable CSIMigration

This walks you through enabling needed feature-gates and explains necessary steps.

The first step is to ebale the feature-gates on the control plane. We again use kubeadm.yaml and kubeadm to perform necessary tasks.

Note: From Kubernetes 1.21 or later, CSIMigrationOpenStack is enabled by default.

apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
kubernetesVersion: "1.17.0-beta.1"
networking:
  podSubnet: 10.96.0.0/16
  serviceSubnet: 10.97.0.0/16
controllerManager:
  extraArgs:
    controllers: "*,bootstrapsigner,tokencleaner,-cloud-node-lifecycle,-route,-service"
    cloud-config: /etc/kubernetes/cloud.conf
    cloud-provider: openstack
  extraVolumes:
  - name: cloud
    hostPath: /etc/kubernetes/cloud.conf
    mountPath: /etc/kubernetes/cloud.conf
    readOnly: true

In this config, we still leave the cloud-provider and cloud-config arguments untouched, but enable the needed feature-gates.

# enable feature-gates for CSIMigration on apiserver and controller-manager
kubeadm init --config ~ubuntu/kubeadm-migrate-1.yaml phase control-plane apiserver
kubeadm init --config ~ubuntu/kubeadm-migrate-1.yaml phase control-plane controller-manager

You must now drain an existing node and enable the feature-gates on kubelet. (At this point, you could also change to --cloud-provider=external and remove the --cloud-config argument)

Note: For kubernetes 1.21 or later, all the feature gates are enabled by default.

cat >> /var/lib/kubelet/config.yaml<<EOF
featureGates:
  CSIMigration: true
  CSIMigrationOpenStack: true
  ExpandCSIVolumes: true
EOF

systemctl restart kubelet

Verify the CSI settings for that particular node:

root@small-k8s-1:~# kubectl get csinode small-k8s-2 -oyaml
apiVersion: storage.k8s.io/v1
kind: CSINode
metadata:
  annotations:
    storage.alpha.kubernetes.io/migrated-plugins: kubernetes.io/cinder
  ...

The first Pod of a StatefulSet scheduled to that node, will get its own VolumeAttachment, and you will find ATTACHER = cinder.csi.openstack.org.

root@small-k8s-1:~# kubectl get volumeattachment
NAME                                                                   ATTACHER                   PV                                         NODE          ATTACHED   AGE
csi-1fa81053386026b068208e1522b3a8db31fd6f9e1828999c34ee555255a3ab13   cinder.csi.openstack.org   pvc-a94be977-8644-4a5f-900b-d1db2a1f8eb9   small-k8s-2   true       2m42s

To migrate all nodes, you must do the same for all of them. Drain, enable feature-gates, uncordon.

Finalize the migration

There are a couple of loose ends remaining. kubelets might still run --cloud-provider=openstack, when you didn't change that during CSIMigration. CCM does not start the controller cloud-node. And kube-controller-manager also still uses a custom configuration. Let's get rid of all that.

On nodes, edit /var/lib/kubelet/kubeadm-flags.env to use --cloud-provider=external and remove --cloud-config=..., and restart kubelet. Head over, and edit the StatefulSet of openstack-cloud-controller-manager to remove the argument --controller=*,-cloud-node. Again, use kubeadm.yaml and kubeadm to remove controllers, cloud-provider and cloud-config.

apiVersion: kubeadm.k8s.io/v1beta2
kind: ClusterConfiguration
kubernetesVersion: "1.17.0-beta.1"
networking:
  podSubnet: 10.96.0.0/16
  serviceSubnet: 10.97.0.0/16
kubeadm init --config ~ubuntu/kubeadm-migrate-final.yaml phase control-plane controller-manager

Caveats

At the time of writing, Kubernetes 1.17.0 is at our doorstep. After a full migration (like you just did), we discovered a problem with deleting PersistentVolumes which have been created before enabling CSIMigration. They still reference the old in-tree provisioner, which is not available any more, because we removed the cloud-config from kube-controller-manager. The workaround for this is rather simple. At some point before removing the PersistentVolume, change the annotation pv.kubernetes.io/provisioned-by to cinder.csi.openstack.org for all old volumes.

e.g.

kubectl annotate --overwrite pv pvc-d4f3d362-66c1-41d5-92b1-b9c07705dec7 pv.kubernetes.io/provisioned-by=cinder.csi.openstack.org

Note: if you haven't done that, but deleted a PersistentVolume, it is still possible to perform this task and trigger another delete. The PersistentVolume will go away, but will leak the corresponding volume in Cinder.