CCM/CSI migration

The CCM/CSI migration is used to migrate your clusters using legacy in-tree cloud provider (i.e. created without .cloudProvider.external: true) to external cloud controller managers (CCMs) and CSI drivers. The CCM/CSI migration process is currently supported only for OpenStack and vSphere.

This guide provides the context on:

  • what are in-tree providers, external CCMs, and CSI drivers
  • why and when do you need to migrate
  • how to migrate your clusters
  • how to troubleshoot failed migration

Support for Cloud Providers in Kubernetes

Cloud providers that want to support advanced Kubernetes use cases can implement Kubernetes controller(s) that would connect Kubernetes clusters with their cloud provider platform/API.

There are three common controllers:

  • Node controller - annotates Node objects with the information about the instance (e.g. instance size, region, availability zone) including IP addresses. It also deletes the Node object when the instance is removed
  • Route controller - configures routes in the cloud appropriately so that containers on different nodes in your Kubernetes cluster can communicate with each other.
  • Service controller - providers support for LoadBalancer Services backed by cloud provider’s Load Balancing offering

In addition, cloud providers can implement controllers for volume operations so that cloud provider’s storage offerings can be used as Kubernetes volumes.

The cloud provider can choose which controllers they want to implement. In other words, they don’t need to implement all those controllers, and they can also implement additional controllers.

In-tree Cloud Providers

In the early days of Kubernetes, those controllers were implemented as part of kube-controller-manager. Those controllers were named as in-tree cloud providers, where the in-tree part was referring to the fact that the code for those controllers was part of the main Kubernetes repository.

This approach worked in the beginning when only very few cloud providers supported Kubernetes. However, as number of providers that support Kubernetes increased, many problems appeared:

  • Having many in-tree cloud providers integrated in kube-controller-manager increases the binary size, while you don’t actually need all providers
  • All providers had to follow the Kubernetes release cycle. If they wanted to change anything in controllers (e.g. they changed the API, added a new feature), they would have to wait for a new Kubernetes release to bring changes to their users
  • Testing and maintaining all the controllers became very complicated

Therefore, it has been decided to deprecate and remove in-tree cloud providers in favor of external cloud controller managers and CSI drivers. It’s expected that in-tree cloud providers will be removed latest by Kubernetes 1.26.

External Cloud Controller Managers (CCMs) and CSI Drivers

External Cloud Controller Manager (CCM) is a set of controllers implemented by cloud providers. Those controllers are not anymore part of the main Kubernetes repository, instead, cloud providers can host them wherever they want. Those controllers also have the same purpose and tasks as in-tree cloud provider controllers. External CCMs are deployed like any other Kubernetes workload (e.g. using Deployments or DaemonSets), however, other control plane components must be configured properly to utilize external CCMs.

However, the controllers for volume operations are not part of the external CCM. Instead, it has been decided to use Container Storage Interface (CSI) for handling volume operations. CSI drivers (or also called plugins) are CSI implementations that are handling all the volume operations, which was originally done by kube-controller-manager. Similar to external CCMs, CSI drivers are also deployed like any other Kubernetes workload.

Who Should Migrate?

If you do not have this section in your KubeOneCluster manifest, then you’re running in-tree cloud provider and you need to migrate.

...
cloudProvider:
  external: true
...

We recommend migrating as soon as possible if your provider is supported because many in-tree providers are not maintained any longer, so new features and improvements are only added to the external CCMs and CSI drivers.

Migration Prerequisites

Make sure to familiarize yourself with requirements for external CCM and CSI drivers. Those requirements are provided by cloud providers and you can usually find them in the repositories for each components:

Migrating Your Clusters

The migration is done in two phases as described below. Before the migration, you need to update your KubeOneCluster manifest as appropriate.

Phase 0 — Preparing your KubeOneCluster manifest

You must set .cloudProvider.external to true, so KubeOne can deploy external CCM and CSI. For example:

apiVersion: kubeone.io/v1beta1
kind: KubeOneCluster
versions:
  kubernetes: 1.22.1
cloudProvider:
  openstack: {}
  external: true
  cloudConfig: |
    ...

In addition to that, specific cloud providers might require additional configuration.

OpenStack

In general, no addition configuration or changes are needed for OpenStack, but make sure to check the documents linked in the Migration Prerequisites section.

vSphere

You should be able to use the same cloudConfig for external CCM as you used before, but make sure to check the documents linked in the Migration Prerequisites section.

However, the vSphere CSI driver has a different configuration file format then external CCM, so you have to provide it in your KubeOneCluster manifest similar to the cloudConfig. The CSI configuration is provided using the csiConfig field, for example:

apiVersion: kubeone.io/v1beta1
kind: KubeOneCluster
versions:
  kubernetes: 1.22.1
cloudProvider:
  openstack: {}
  external: true
  cloudConfig: |
    ...
  csiConfig: |
    ...

Check out the Create a configuration file with vSphere credentials section of the vSphere CSI Installation document for more details on how to create the configuration file. In general, the configuration file can be similar to the cloudConfig configuration with the following changes:

  • credentials must be provided in plain-text using user and password instead of secret-name and secret-namespace
  • the cluster-id must be set to the name of the vSphere Cluster resource

Phase 1 — Deploying External CCM and CSI Plugin, with in-tree cloud provider enabled

The first phase assumes deploying the external CCM and CSI plugin, while leaving in-tree provider enabled. Kubernetes API server and kube-controller-manager are configured to:

  • use controllers integrated in external CCM instead of in-tree cloud provider for all cloud-related operations
  • redirect all volumes-related operations to the CSI plugin

The existing worker nodes will continue to use in-tree provider, and that’s why we still leave it enabled on API server and kube-controller-manager. Therefore, all worker nodes managed by machine-controller must be rolled out after phase 1 is complete.

To start the first phase of the migration, run the following command. You’ll be asked to confirm your intention by typing yes.

kubeone migrate to-ccm-csi --manifest kubeone.yaml -t tf.json

This command might take 5-10 minutes to finish. After it’s done, you need to roll out all your worker nodes managed by machine-controller, so they start using external CCM and CSI.

The Rolling Restart MachineDeploments document describes possible approaches for rotating worker nodes. You can use the following command to rotate all worker nodes at the same time. For additional approaches, please check the document.

forceRestartAnnotations="{\"spec\":{\"template\":{\"metadata\":{\"annotations\":{\"forceRestart\":\"$(date +%N)\"}}}}}"
for md in $(kubectl get machinedeployments -n kube-system --no-headers | awk '{print $1}'); do
  kubectl patch machinedeployment -n kube-system $md --type=merge -p $forceRestartAnnotations
done

You can watch the progress by running kubectl get nodes. Make sure that all worker nodes are rotated before proceeding to the next phase.

Phase 2 — Completely disabling in-tree cloud provider

The CCM/CSI migration is completed by fully-disabling in-tree provider. To trigger the phase 2, users first need to rotate all their worker nodes managed by machine-controller as described in the previous phase.

After all worker nodes are rotated, you can run the following command to complete the migration:

kubeone migrate to-ccm-csi --complete --manifest kubeone.yaml -t tf.json

This command might take up to 5 minutes to finish. After this command is done, the CCM/CSI migration is fully-completed. Congratulations!

Alternatives to the CCM/CSI migration

Alternative to the CCM/CSI migration is recreating the cluster from scratch with .cloudProvider.external enabled from the beginning. While that approach would give you a fresh cluster, it might be complicated because:

  • you need to recreate all the resources and re-deploy the workload. This might cause some downtime, and it can be very complicated in case you have stateful workload
  • you need to manually migrate existing PersistentVolumes to the new cluster

Restoring from a backup in case of recreating the cluster is not an option because that might also restore the old configuration and eventually break the cluster.