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Migrate etcd

By following the given steps, you can successfully migrate etcd from one node to another during maintenance activities like node drain etc., ensuring the continuity and integrity of the etcd data.
Take a snapshot of the etcd. Click here for the detailed documentation.

Step 1: Draining the etcd Node

  1. 1.
    Assuming we have a three-node cluster with three etcd replicas, verify the etcd pods with the following commands:
Command to verify pods:
Command
Output
kubectl get pods -n mayastor -l app=etcd -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
mayastor-etcd-0 1/1 Running 0 4m9s 10.244.1.212 worker-1 <none> <none>
mayastor-etcd-1 1/1 Running 0 5m16s 10.244.2.219 worker-2 <none> <none>
mayastor-etcd-2 1/1 Running 0 6m28s 10.244.3.203 worker-0 <none> <none>
  1. 2.
    From etcd-0/1/2 we could see all the values are registered in database, once we migrated etcd to new node, all the key-value pairs should be available across all the pods. Run the following commands from any etcd pod.
Commands to get etcd data:
Command
kubectl exec -it mayastor-etcd-0 -n mayastor -- bash
#ETCDCTL_API=3
#etcdctl get --prefix ""
  1. 3.
    In this example, we drain the etcd node worker-0 and migrate it to the next available node (in this case, the worker-4 node), use the following command:
Command to drain the node:
Command
Output
kubectl drain worker-0 --ignore-daemonsets --delete-emptydir-data
node/worker-0 cordoned
Warning: ignoring DaemonSet-managed Pods: kube-system/kube-flannel-ds-pbm7r, kube-system/kube-proxy-jgjs4, mayastor/mayastor-agent-ha-node-jkd4c, mayastor/mayastor-csi-node-mb89n, mayastor/mayastor-io-engine-q2n28, mayastor/mayastor-promethues-prometheus-node-exporter-v6mfs, mayastor/mayastor-promtail-6vgvm, monitoring/node-exporter-fz247
evicting pod mayastor/mayastor-etcd-2
evicting pod mayastor/mayastor-agent-core-7c594ff676-2ph69
evicting pod mayastor/mayastor-operator-diskpool-c8ddb588-cgr29
pod/mayastor-operator-diskpool-c8ddb588-cgr29 evicted
pod/mayastor-agent-core-7c594ff676-2ph69 evicted
pod/mayastor-etcd-2 evicted
node/worker-0 drained

Step 2: Migrating etcd to the New Node

  1. 1.
    After draining the worker-0 node, the etcd pod will be scheduled on the next available node, which is the worker-4 node.
  2. 2.
    The pod may end up in a CrashLoopBackOff status with specific errors in the logs.
  3. 3.
    When the pod is scheduled on the new node, it attempts to bootstrap the member again, but since the member is already registered in the cluster, it fails to start the etcd server with the error message member already bootstrapped.
  4. 4.
    To fix this issue, change the cluster's initial state from new to existing by editing the StatefulSet for etcd:
Command to check new etcd pod status
Command
Output
kubectl get pods -n mayastor -l app=etcd -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
mayastor-etcd-0 1/1 Running 0 35m 10.244.1.212 worker-1 <none> <none>
mayastor-etcd-1 1/1 Running 0 36m 10.244.2.219 worker-2 <none> <none>
mayastor-etcd-2 0/1 CrashLoopBackOff 5 (44s ago) 10m 10.244.0.121 worker-4 <none> <none>
Command to edit the StatefulSet:
Command
Output
kubectl edit sts mayastor-etcd -n mayastor
- name: ETCD_INITIAL_CLUSTER_STATE
value: existing

Step 3: Validating etcd Key-Value Pairs

Run the appropriate command from the migrated etcd pod to validate the key-value pairs and ensure they are the same as in the existing etcd. This step is crucial to avoid any data loss during the migration process.
Command
kubectl exec -it mayastor-etcd-0 -n mayastor -- bash
#ETCDCTL_API=3
#etcdctl get --prefix ""