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Changing the Container Runtime on a Node from Docker Engine to containerd

This task outlines the steps needed to update your container runtime to containerd from Docker. It is applicable for cluster operators running Kubernetes 1.23 or earlier. This also covers an example scenario for migrating from dockershim to containerd. Alternative container runtimes can be picked from this page.

Before you begin

Install containerd. For more information see containerd's installation documentation and for specific prerequisite follow the containerd guide.

Drain the node

kubectl drain <node-to-drain> --ignore-daemonsets

Replace <node-to-drain> with the name of your node you are draining.

Stop the Docker daemon

systemctl stop kubelet
systemctl disable docker.service --now

Install Containerd

Follow the guide for detailed steps to install containerd.

  1. Install the containerd.io package from the official Docker repositories. Instructions for setting up the Docker repository for your respective Linux distribution and installing the containerd.io package can be found at Getting started with containerd.

  2. Configure containerd:

    sudo mkdir -p /etc/containerd
    containerd config default | sudo tee /etc/containerd/config.toml
    
  3. Restart containerd:

    sudo systemctl restart containerd
    

Start a Powershell session, set $Version to the desired version (ex: $Version="1.4.3"), and then run the following commands:

  1. Download containerd:

    curl.exe -L https://github.com/containerd/containerd/releases/download/v$Version/containerd-$Version-windows-amd64.tar.gz -o containerd-windows-amd64.tar.gz
    tar.exe xvf .\containerd-windows-amd64.tar.gz
    
  2. Extract and configure:

    Copy-Item -Path ".\bin\" -Destination "$Env:ProgramFiles\containerd" -Recurse -Force
    cd $Env:ProgramFiles\containerd\
    .\containerd.exe config default | Out-File config.toml -Encoding ascii
    
    # Review the configuration. Depending on setup you may want to adjust:
    # - the sandbox_image (Kubernetes pause image)
    # - cni bin_dir and conf_dir locations
    Get-Content config.toml
    
    # (Optional - but highly recommended) Exclude containerd from Windows Defender Scans
    Add-MpPreference -ExclusionProcess "$Env:ProgramFiles\containerd\containerd.exe"
    
  3. Start containerd:

    .\containerd.exe --register-service
    Start-Service containerd
    

Configure the kubelet to use containerd as its container runtime

Edit the file /var/lib/kubelet/kubeadm-flags.env and add the containerd runtime to the flags. --container-runtime=remote and --container-runtime-endpoint=unix:///run/containerd/containerd.sock.

Users using kubeadm should be aware that the kubeadm tool stores the CRI socket for each host as an annotation in the Node object for that host. To change it you can execute the following command on a machine that has the kubeadm /etc/kubernetes/admin.conf file.

kubectl edit no <node-name>

This will start a text editor where you can edit the Node object. To choose a text editor you can set the KUBE_EDITOR environment variable.

  • Change the value of kubeadm.alpha.kubernetes.io/cri-socket from /var/run/dockershim.sock to the CRI socket path of your choice (for example unix:///run/containerd/containerd.sock).

    Note that new CRI socket paths must be prefixed with unix:// ideally.

  • Save the changes in the text editor, which will update the Node object.

Restart the kubelet

systemctl start kubelet

Verify that the node is healthy

Run kubectl get nodes -o wide and containerd appears as the runtime for the node we just changed.

Remove Docker Engine

Finally if everything goes well, remove Docker.

sudo yum remove docker-ce docker-ce-cli

sudo apt-get purge docker-ce docker-ce-cli

sudo dnf remove docker-ce docker-ce-cli

sudo apt-get purge docker-ce docker-ce-cli

The preceding commands don't remove images, containers, volumes, or customized configuration files on your host. To delete them, follow Docker's instructions to Uninstall Docker Engine.

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Last modified July 25, 2022 at 11:45 PM PST: Fix minor typo (#35296) (b396da8a94)