Replacing a failed etcd replica

This page describes how to replace a failed etcd replica in a high availability (HA) user cluster for Google Distributed Cloud.

Before you begin

  • Make sure the admin cluster is working correctly.

  • Make sure the other two etcd members in the user cluster are working correctly. If more than one etcd member has failed, see Recovery from etcd data corruption or loss.

Replacing a failed etcd replica

  1. Back up a copy of the etcd PodDisruptionBudget (PDB) so you can restore it later.

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG -n USER_CLUSTER_NAME get pdb kube-etcd-pdb -o yaml > PATH_TO_PDB_FILE

    Where:

    • ADMIN_CLUSTER_KUBECONFIG is the path to the kubeconfig file for the admin cluster.

    • USER_CLUSTER_NAME is the name of the user cluster that contains the failed etcd replica.

    • PATH_TO_PDB_FILE is the path where you want to save the etcd PDB file, for instance /tmp/etcpdb.yaml.

  2. Delete the etcd PodDisruptionBudget (PDB).

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG -n USER_CLUSTER_NAME delete pdb kube-etcd-pdb
  3. Run the following command to open the kube-etcd StatefulSet in your text editor:

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG -n USER_CLUSTER_NAME edit statefulset kube-etcd

    Change the value of the --initial-cluster-state flag to existing.

    containers:
        - name: kube-etcd
          ...
          args:
            - --initial-cluster-state=existing
          ...
     
  4. Drain the failed etcd replica node.

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG drain NODE_NAME --ignore-daemonsets --delete-local-data

    Where NODE_NAME is the name of the failed etcd replica node.

  5. Create a new shell in the container of one of the working kube-etcd pods.

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG exec -it \
       KUBE_ETCD_POD --container kube-etcd --namespace USER_CLUSTER_NAME \
       -- bin/sh

    Where KUBE_ETCD_POD is the name of the working kube-etcd pod. For example, kube-etcd-0.

    From this new shell, run the following commands:

    1. Remove the failed etcd replica node from the etcd cluster.

      First, list all the members of the etcd cluster:

      etcdctl member list -w table

      The output shows all the member IDs. Determine the member ID of the failed replica.

      Next, remove the failed replica:

      export ETCDCTL_CACERT=/etcd.local.config/certificates/etcdCA.crt
      export ETCDCTL_CERT=/etcd.local.config/certificates/etcd.crt
      export ETCDCTL_CERT=/etcd.local.config/certificates/etcd.crt
      export ETCDCTL_KEY=/etcd.local.config/certificates/etcd.key
      export ETCDCTL_ENDPOINTS=https://127.0.0.1:2379
      etcdctl member remove MEMBER_ID

      Where MEMBER_ID is the hex member ID of the failed etcd replica pod.

    2. Add a new member with the same name and peer URL as the failed replica node.

      etcdctl member add MEMBER_NAME --peer-urls=https://MEMBER_NAME.kube-etcd:2380

      Where MEMBER_NAME is the identifier of the failed kube-etcd replica node. For example, kube-etcd-1 or kube-etcd2.

  6. Follow steps 1-3 of Deploying the utility Pods to create a utility Pod in the admin cluster. This Pod is used to access the PersistentVolume (PV) of the failed etcd member in the user cluster.

  7. Clean up the etcd data directory from within the utility Pod.

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG exec -it -n USER_CLUSTER_NAME etcd-utility-MEMBER_NUMBER -- /bin/bash -c 'rm -rf /var/lib/etcd/*'
  8. Delete the utility Pod.

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG delete pod -n USER_CLUSTER_NAME etcd-utility-MEMBER_NUMBER
  9. Uncordon the failed node.

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG uncordon NODE_NAME
  10. Open the kube-etcd StatefulSet in your text editor.

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG -n USER_CLUSTER_NAME edit statefulset kube-etcd

    Change the value of the --initial-cluster-state flag to new.

    containers:
        - name: kube-etcd
          ...
          args:
            - --initial-cluster-state=new
          ...
     
  11. Restore the etcd PDB which was deleted in step 1.

    kubectl --kubeconfig ADMIN_CLUSTER_KUBECONFIG apply -f /path/to/etcdpdb.yaml