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Backing up and restoring etcd in an on-premise environment - High availability for hosted control planes | Hosted control planes | OpenShift Container Platform 4.16
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Backing up and restoring etcd in an on-premise environment

You can back up and restore etcd on a hosted cluster in an on-premise environment to fix failures.

Backing up and restoring etcd on a hosted cluster in an on-premise environment

By backing up and restoring etcd on a hosted cluster, you can fix failures, such as corrupted or missing data in an etcd member of a three node cluster. If multiple members of the etcd cluster encounter data loss or have a CrashLoopBackOff status, this approach helps prevent an etcd quorum loss.

This procedure requires API downtime.
Prerequisites

  • The oc and jq binaries have been installed.

Procedure

  1. First, set up your environment variables and scale down the API servers:

    1. Set up environment variables for your hosted cluster by entering the following commands, replacing values as necessary:

      $ CLUSTER_NAME=my-cluster
      $ HOSTED_CLUSTER_NAMESPACE=clusters
      $ CONTROL_PLANE_NAMESPACE="${HOSTED_CLUSTER_NAMESPACE}-${CLUSTER_NAME}"

    2. Pause reconciliation of the hosted cluster by entering the following command, replacing values as necessary:

      $ oc patch -n ${HOSTED_CLUSTER_NAMESPACE} hostedclusters/${CLUSTER_NAME} -p '{"spec":{"pausedUntil":"true"}}' --type=merge

    3. Scale down the API servers by entering the following commands:

      1. Scale down the kube-apiserver:

        $ oc scale -n ${CONTROL_PLANE_NAMESPACE} deployment/kube-apiserver --replicas=0

      2. Scale down the openshift-apiserver:

        $ oc scale -n ${CONTROL_PLANE_NAMESPACE} deployment/openshift-apiserver --replicas=0

      3. Scale down the openshift-oauth-apiserver:

        $ oc scale -n ${CONTROL_PLANE_NAMESPACE} deployment/openshift-oauth-apiserver --replicas=0

  2. Next, take a snapshot of etcd by using one of the following methods:

    1. Use a previously backed-up snapshot of etcd.

    2. If you have an available etcd pod, take a snapshot from the active etcd pod by completing the following steps:

      1. List etcd pods by entering the following command:

        $ oc get -n ${CONTROL_PLANE_NAMESPACE} pods -l app=etcd

      2. Take a snapshot of the pod database and save it locally to your machine by entering the following commands:

        $ ETCD_POD=etcd-0
        $ oc exec -n ${CONTROL_PLANE_NAMESPACE} -c etcd -t ${ETCD_POD} -- env ETCDCTL_API=3 /usr/bin/etcdctl \
--cacert /etc/etcd/tls/etcd-ca/ca.crt \
--cert /etc/etcd/tls/client/etcd-client.crt \
--key /etc/etcd/tls/client/etcd-client.key \
--endpoints=https://localhost:2379 \
snapshot save /var/lib/snapshot.db

      3. Verify that the snapshot is successful by entering the following command:

        $ oc exec -n ${CONTROL_PLANE_NAMESPACE} -c etcd -t ${ETCD_POD} -- env ETCDCTL_API=3 /usr/bin/etcdctl -w table snapshot status /var/lib/snapshot.db

    3. Make a local copy of the snapshot by entering the following command:

      $ oc cp -c etcd ${CONTROL_PLANE_NAMESPACE}/${ETCD_POD}:/var/lib/snapshot.db /tmp/etcd.snapshot.db

      1. Make a copy of the snapshot database from etcd persistent storage:

        1. List etcd pods by entering the following command:

          $ oc get -n ${CONTROL_PLANE_NAMESPACE} pods -l app=etcd

        2. Find a pod that is running and set its name as the value of ETCD_POD: ETCD_POD=etcd-0, and then copy its snapshot database by entering the following command:

          $ oc cp -c etcd ${CONTROL_PLANE_NAMESPACE}/${ETCD_POD}:/var/lib/data/member/snap/db /tmp/etcd.snapshot.db

  3. Next, scale down the etcd statefulset by entering the following command:

    $ oc scale -n ${CONTROL_PLANE_NAMESPACE} statefulset/etcd --replicas=0

    1. Delete volumes for second and third members by entering the following command:

      $ oc delete -n ${CONTROL_PLANE_NAMESPACE} pvc/data-etcd-1 pvc/data-etcd-2

    2. Create a pod to access the first etcd member’s data:

      1. Get the etcd image by entering the following command:

        $ ETCD_IMAGE=$(oc get -n ${CONTROL_PLANE_NAMESPACE} statefulset/etcd -o jsonpath='{ .spec.template.spec.containers[0].image }')

      2. Create a pod that allows access to etcd data:

        $ cat << EOF | oc apply -n ${CONTROL_PLANE_NAMESPACE} -f -
apiVersion: apps/v1
kind: deployment
metadata:
  name: etcd-data
spec:
  replicas: 1
  selector:
    matchLabels:
      app: etcd-data
  template:
    metadata:
      labels:
        app: etcd-data
    spec:
      containers:
      - name: access
        image: $ETCD_IMAGE
        volumeMounts:
        - name: data
          mountPath: /var/lib
        command:
        - /usr/bin/bash
        args:
        - -c
        - |-
          while true; do
            sleep 1000
          done
      volumes:
      - name: data
        persistentVolumeClaim:
          claimName: data-etcd-0
EOF

      3. Check the status of the etcd-data pod and wait for it to be running by entering the following command:

        $ oc get -n ${CONTROL_PLANE_NAMESPACE} pods -l app=etcd-data

      4. Get the name of the etcd-data pod by entering the following command:

        $ DATA_POD=$(oc get -n ${CONTROL_PLANE_NAMESPACE} pods --no-headers -l app=etcd-data -o name | cut -d/ -f2)

    3. Copy an etcd snapshot into the pod by entering the following command:

      $ oc cp /tmp/etcd.snapshot.db ${CONTROL_PLANE_NAMESPACE}/${DATA_POD}:/var/lib/restored.snap.db

    4. Remove old data from the etcd-data pod by entering the following commands:

      $ oc exec -n ${CONTROL_PLANE_NAMESPACE} ${DATA_POD} -- rm -rf /var/lib/data
      $ oc exec -n ${CONTROL_PLANE_NAMESPACE} ${DATA_POD} -- mkdir -p /var/lib/data

    5. Restore the etcd snapshot by entering the following command:

      $ oc exec -n ${CONTROL_PLANE_NAMESPACE} ${DATA_POD} -- etcdutl snapshot restore /var/lib/restored.snap.db \
     --data-dir=/var/lib/data --skip-hash-check \
     --name etcd-0 \
     --initial-cluster-token=etcd-cluster \
     --initial-cluster etcd-0=https://etcd-0.etcd-discovery.${CONTROL_PLANE_NAMESPACE}.svc:2380,etcd-1=https://etcd-1.etcd-discovery.${CONTROL_PLANE_NAMESPACE}.svc:2380,etcd-2=https://etcd-2.etcd-discovery.${CONTROL_PLANE_NAMESPACE}.svc:2380 \
     --initial-advertise-peer-urls https://etcd-0.etcd-discovery.${CONTROL_PLANE_NAMESPACE}.svc:2380

    6. Remove the temporary etcd snapshot from the pod by entering the following command:

      $ oc exec -n ${CONTROL_PLANE_NAMESPACE} ${DATA_POD} -- rm /var/lib/restored.snap.db

    7. Delete data access deployment by entering the following command:

      $ oc delete -n ${CONTROL_PLANE_NAMESPACE} deployment/etcd-data

    8. Scale up the etcd cluster by entering the following command:

      $ oc scale -n ${CONTROL_PLANE_NAMESPACE} statefulset/etcd --replicas=3

    9. Wait for the etcd member pods to return and report as available by entering the following command:

      $ oc get -n ${CONTROL_PLANE_NAMESPACE} pods -l app=etcd -w

    10. Scale up all etcd-writer deployments by entering the following command:

      $ oc scale deployment -n ${CONTROL_PLANE_NAMESPACE} --replicas=3 kube-apiserver openshift-apiserver openshift-oauth-apiserver

  4. Restore reconciliation of the hosted cluster by entering the following command:

    $ oc patch -n ${CLUSTER_NAMESPACE} hostedclusters/${CLUSTER_NAME} -p '{"spec":{"pausedUntil":""}}' --type=merge