Migrate from dockershim to containerd

Kubernetes no longer supports dockershim. The Kubernetes team removed the runtime in Kubernetes version 1.24. For more information, see Kubernetes is Moving on From Dockershim: Commitments and Next Steps on the Kubernetes Blog.

Amazon EKS also ended support for dockershim starting with the Kubernetes version 1.24 release. Amazon EKS AMIs that are officially published have containerd as the only runtime starting with version 1.24. This topic covers some details, but more information is available in All you need to know about moving to containerd on Amazon EKS.

There’s a kubectl plugin that you can use to see which of your Kubernetes workloads mount the Docker socket volume. For more information, see Detector for Docker Socket (DDS) on GitHub. Amazon EKS AMIs that run Kubernetes versions that are earlier than 1.24 use Docker as the default runtime. However, these Amazon EKS AMIs have a bootstrap flag option that you can use to test out your workloads on any supported cluster using containerd. For more information, see Test Amazon Linux 2 migration from Docker to containerd.

We will continue to publish AMIs for existing Kubernetes versions until the end of their support date. For more information, see Amazon EKS Kubernetes release calendar. If you require more time to test your workloads on containerd, use a supported version before 1.24. But, when you want to upgrade official Amazon EKS AMIs to version 1.24 or later, make sure to validate that your workloads run on containerd.

The containerd runtime provides more reliable performance and security. containerd is the runtime that’s being standardized on across Amazon EKS. Fargate and Bottlerocket already use containerd only. containerd helps to minimize the number of Amazon EKS AMI releases that are required to address dockershim Common Vulnerabilities and Exposures (CVEs). Because dockershim already uses containerd internally, you might not need to make any changes. However, there are some situations where changes might or must be required:

• You must make changes to applications that mount the Docker socket. For example, container images that are built with a container are impacted. Many monitoring tools also mount the Docker socket. You might need to wait for updates or re-deploy workloads for runtime monitoring.

• You might need to make changes for applications that are reliant on specific Docker settings. For example, the HTTPS_PROXY protocol is no longer supported. You must update applications that use this protocol. For more information, see dockerd in the Docker Documentation.

• If you use the Amazon ECR credential helper to pull images, you must switch to the kubelet image credential provider. For more information, see Configure a kubelet image credential provider in the Kubernetes documentation.

• Because Amazon EKS 1.24 no longer supports Docker, some flags that the Amazon EKS bootstrap script previously supported are no longer supported. Before moving to Amazon EKS 1.24 or later, you must remove any reference to flags that are now unsupported:

  • --container-runtime dockerd (containerd is the only supported value)

  • --enable-docker-bridge

  • --docker-config-json

• If you already have Fluentd configured for Container Insights, then you must migrate Fluentd to Fluent Bit before changing to containerd. The Fluentd parsers are configured to only parse log messages in JSON format. Unlike dockerd, the containerd container runtime has log messages that aren’t in JSON format. If you don’t migrate to Fluent Bit, some of the configured Fluentd’s parsers will generate a massive amount of errors inside the Fluentd container. For more information on migrating, see Set up Fluent Bit as a DaemonSet to send logs to CloudWatch Logs.

• If you use a custom AMI and you are upgrading to Amazon EKS 1.24, then you must make sure that IP forwarding is enabled for your worker nodes. This setting wasn’t needed with Docker but is required for containerd. It is needed to troubleshoot Pod-to-Pod, Pod-to-external, or Pod-to-apiserver network connectivity.

  To verify this setting on a worker node, run either of the following commands:

  • sysctl net.ipv4.ip_forward

  • cat /proc/sys/net/ipv4/ip_forward

  If the output is 0, then run either of the following commands to activate the net.ipv4.ip_forward kernel variable:

  • sysctl -w net.ipv4.ip_forward=1

  • echo 1 > /proc/sys/net/ipv4/ip_forward

For the setting’s activation on Amazon EKS AMIs for Amazon Linux 2 in the containerd runtime, see install-worker.sh on GitHub.

Test Amazon Linux 2 migration from Docker to containerd

For Kubernetes version 1.23, you can use an optional bootstrap flag to enable the containerd runtime for Amazon EKS optimized AL2 AMIs. This feature gives you a clear path to migrate to containerd when updating to version 1.24 or later. Amazon EKS ended support for Docker starting with the Kubernetes version 1.24 launch. The containerd runtime is widely adopted in the Kubernetes community and is a graduated project with the CNCF. You can test it by adding a node group to a new or existing cluster.

You can enable the boostrap flag by creating one of the following types of node groups.

Self-managed

Create the node group using the instructions in Create self-managed Amazon Linux nodes. Specify an Amazon EKS optimized AMI and the following text for the BootstrapArguments parameter.

--container-runtime containerd

Managed

If you use eksctl, create a file named my-nodegroup.yaml with the following contents. Replace every example value with your own values. The node group name can’t be longer than 63 characters. It must start with letter or digit, but can also include hyphens and underscores for the remaining characters. To retrieve an optimized AMI ID for ami-1234567890abcdef0 , see Retrieve recommended Amazon Linux AMI IDs.

apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig
metadata:
  name: my-cluster
  region: region-code
  version: 1.23
managedNodeGroups:
  - name: my-nodegroup
    ami: ami-1234567890abcdef0
    overrideBootstrapCommand: |
      #!/bin/bash
      /etc/eks/bootstrap.sh my-cluster --container-runtime containerd

Note

If you launch many nodes simultaneously, you may also want to specify values for the --apiserver-endpoint, --b64-cluster-ca, and --dns-cluster-ip bootstrap arguments to avoid errors. For more information, see Specifying an AMI.

Run the following command to create the node group.

eksctl create nodegroup -f my-nodegroup.yaml

If you prefer to use a different tool to create your managed node group, you must deploy the node group using a launch template. In your launch template, specify an Amazon EKS optimized AMI ID, then deploy the node group using a launch template and provide the following user data. This user data passes arguments into the bootstrap.sh file. For more information about the bootstrap file, see bootstrap.sh on GitHub.

/etc/eks/bootstrap.sh my-cluster --container-runtime containerd