Added documentation for this feature

userdocs/mkdocs.yml

@@ -35,6 +35,7 @@ nav:
             - usage/arm-support.md
             - usage/autoscaling.md
             - usage/custom-ami-support.md
+            - usage/container-runtime.md
             - usage/windows-worker-nodes.md
         - GitOps:
             - usage/gitops-v2.md

userdocs/src/usage/container-runtime.md

@@ -0,0 +1,68 @@
+# Define Container Runtime
+
+For AL2 ( AmazonLinux2 ) AMIs it's possible to set container runtime to `containerd`.
+
+## Un-managed Nodes
+
+For un-managed nodes, simply provide the following configuration when creating a new node:
+
+```yaml
+apiVersion: eksctl.io/v1alpha5
+kind: ClusterConfig
+
+metadata:
+  name: container-runtime-test
+  region: us-west-2
+
+nodeGroups:
+  - name: ng-1
+    labels: { role: web }
+    instanceType: m5.xlarge
+    desiredCapacity: 10
+    privateNetworking: true
+    amiFamily: AmazonLinux2
+    containerRuntime: containerd
+  - name: ng-2-api
+    labels: { role: api }
+    instanceType: m5.2xlarge
+    desiredCapacity: 2
+    privateNetworking: true
+```
+
+This value is set to `dockerd` by default to preserve backwards compatibility, but will soon be
+deprecated.
+
+The container runtime value is then passed to the bootstrap.sh script by `eksctl` as follows:
+
+```bash
+/etc/eks/bootstrap.sh "${CLUSTER_NAME}" \
+  ...
+  --container-runtime "${CONTAINER_RUNTIME}"
+```
+
+At the time of this writing the following container runtime values are allowed:
+
+- containerd
+- dockerd
+
+## Managed Nodes
+
+For managed nodes we don't explicitly provide a bootstrap script, and thus it's up to the user
+to define a different runtime if they wish, using `overrideBootstrapCommand`:
+
+```yaml
+nodeGroups:
+  - name: ng1
+    instanceType: p2.xlarge
+    ami: auto
+  - name: ng2
+    instanceType: m5.large
+    ami: ami-custom1234
+managedNodeGroups:
+  - name: m-ng-2
+    ami: ami-custom1234
+    instanceType: m5.large
+    overrideBootstrapCommand: |
+      #!/bin/bash
+      /etc/eks/bootstrap.sh <cluster-name> --container-runtime containerd
+```