Migrate Docker Engine nodes from dockershim to cri-dockerd

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This page shows you how to migrate your Docker Engine nodes to use cri-dockerd instead of dockershim. You should follow these steps in these scenarios:

  • You want to switch away from dockershim and still use Docker Engine to run containers in Kubernetes.
  • You want to upgrade to Kubernetes v1.24 and your existing cluster relies on dockershim, in which case you must migrate from dockershim and cri-dockerd is one of your options.

To learn more about the removal of dockershim, read the FAQ page.

What is cri-dockerd?

In Kubernetes 1.23 and earlier, you could use Docker Engine with Kubernetes, relying on a built-in component of Kubernetes named dockershim. The dockershim component was removed in the Kubernetes 1.24 release; however, a third-party replacement, cri-dockerd, is available. The cri-dockerd adapter lets you use Docker Engine through the Container Runtime Interface.

Note: If you already use cri-dockerd, you aren’t affected by the dockershim removal. Before you begin, Check whether your nodes use the dockershim.

If you want to migrate to cri-dockerd so that you can continue using Docker Engine as your container runtime, you should do the following for each affected node:

  1. Install cri-dockerd.
  2. Cordon and drain the node.
  3. Configure the kubelet to use cri-dockerd.
  4. Restart the kubelet.
  5. Verify that the node is healthy.

Test the migration on non-critical nodes first.

You should perform the following steps for each node that you want to migrate to cri-dockerd.

Before you begin

Cordon and drain the node

  1. Cordon the node to stop new Pods scheduling on it:

    1. kubectl cordon <NODE_NAME>

    Replace <NODE_NAME> with the name of the node.

  2. Drain the node to safely evict running Pods:

    1. kubectl drain <NODE_NAME> \
    2.     --ignore-daemonsets

Configure the kubelet to use cri-dockerd

The following steps apply to clusters set up using the kubeadm tool. If you use a different tool, you should modify the kubelet using the configuration instructions for that tool.

  1. Open /var/lib/kubelet/kubeadm-flags.env on each affected node.
  2. Modify the --container-runtime-endpoint flag to unix:///var/run/cri-dockerd.sock.

The kubeadm tool stores the node’s socket as an annotation on the Node object in the control plane. To modify this socket for each affected node:

  1. Edit the YAML representation of the Node object:

    1. KUBECONFIG=/path/to/admin.conf kubectl edit no <NODE_NAME>

    Replace the following:

    • /path/to/admin.conf: the path to the kubectl configuration file, admin.conf.
    • <NODE_NAME>: the name of the node you want to modify.

  2. Change kubeadm.alpha.kubernetes.io/cri-socket from /var/run/dockershim.sock to unix:///var/run/cri-dockerd.sock.

  3. Save the changes. The Node object is updated on save.

Restart the kubelet

  1. systemctl restart kubelet

Verify that the node is healthy

To check whether the node uses the cri-dockerd endpoint, follow the instructions in Find out which runtime you use. The --container-runtime-endpoint flag for the kubelet should be unix:///var/run/cri-dockerd.sock.

Uncordon the node

Uncordon the node to let Pods schedule on it:

  1. kubectl uncordon <NODE_NAME>

What’s next