EKS Auto Mode clusters need vpc-cni addon before adding managed node groups

I added a managed node group to an EKS Auto Mode cluster and it went straight to CREATE_FAILED.

Output

{
  "code": "NodeCreationFailure",
  "message": "Unhealthy nodes in the kubernetes cluster"
}

kubectl describe node revealed the root cause — no CNI plugin.

Output

Ready   False   KubeletNotReady   container runtime network not ready:
  NetworkReady=false reason:NetworkPluginNotReady
  message:Network plugin returns error: cni plugin not initialized

Auto Mode clusters use their own networking, so vpc-cni, kube-proxy, and coredns aren't installed by default. Managed node groups depend on these, so you need to add them first.

Terminal

aws eks create-addon --cluster-name $CLUSTER --addon-name vpc-cni --region $REGION
aws eks create-addon --cluster-name $CLUSTER --addon-name kube-proxy --region $REGION
aws eks create-addon --cluster-name $CLUSTER --addon-name coredns --region $REGION

After the addons reached ACTIVE, recreating the node groups worked — all nodes came up Ready. Hit this during the warm pool verification article setup.