Decommission a Specific Pod in KubeBlocks-Managed Elasticsearch Clusters

This guide explains how to decommission (take offline) specific Pods in Elasticsearch clusters managed by KubeBlocks. Decommissioning provides precise control over cluster resources while maintaining availability. Use this for workload rebalancing, node maintenance, or addressing failures.

Why Decommission Pods with KubeBlocks?

In traditional StatefulSet-based deployments, Kubernetes lacks the ability to decommission specific Pods. StatefulSets ensure the order and identity of Pods, and scaling down always removes the Pod with the highest ordinal number (e.g., scaling down from 3 replicas removes Pod-2 first). This limitation prevents precise control over which Pod to take offline, which can complicate maintenance, workload distribution, or failure handling.

KubeBlocks overcomes this limitation by enabling administrators to decommission specific Pods directly. This fine-grained control ensures high availability and allows better resource management without disrupting the entire cluster.

Prerequisites

Before proceeding, ensure the following:

• Environment Setup:
  • A Kubernetes cluster is up and running.
  • The kubectl CLI tool is configured to communicate with your cluster.
  • KubeBlocks CLI and KubeBlocks Operator are installed. Follow the installation instructions here.
• Namespace Preparation: To keep resources isolated, create a dedicated namespace for this tutorial:

kubectl create ns demo
namespace/demo created

Deploy a Elasticsearch Cluster

KubeBlocks uses a declarative approach for managing Elasticsearch Clusters. Below is an example configuration for deploying a Elasticsearch Cluster with create a cluster with replicas for different roles.

Apply the following YAML configuration to deploy the cluster:

apiVersion: apps.kubeblocks.io/v1
kind: Cluster
metadata:
  name: es-multinode
  namespace: demo
spec:
  terminationPolicy: Delete
  componentSpecs:
    - name: dit
      componentDef: elasticsearch-8
      serviceVersion: 8.8.2
      configs:
        - name: es-cm
          variables:
            # use key `roles` to specify roles this component assume
            roles: data,ingest,transform
      replicas: 3
      disableExporter: false
      resources:
        limits:
          cpu: "1"
          memory: "2Gi"
        requests:
          cpu: "1"
          memory: "2Gi"
      volumeClaimTemplates:
        - name: data
          spec:
            accessModes:
              - ReadWriteOnce
            resources:
              requests:
                storage: 20Gi
    - name: master
      componentDef: elasticsearch-8
      serviceVersion: 8.8.2
      configs:
        - name: es-cm
          variables:
            # use key `roles` to specify roles this component assume
            roles: master
      replicas: 3
      disableExporter: false
      resources:
        limits:
          cpu: "1"
          memory: "2Gi"
        requests:
          cpu: "1"
          memory: "2Gi"
      volumeClaimTemplates:
        - name: data
          spec:
            accessModes:
              - ReadWriteOnce
            resources:
              requests:
                storage: 20Gi

Verifying the Deployment

Monitor the cluster status until it transitions to the Running state:

kubectl get cluster es-multinode -n demo -w

Expected Output:

NAME           CLUSTER-DEFINITION   TERMINATION-POLICY   STATUS     AGE
es-multinode                        Delete               Creating   10s
es-multinode                        Delete               Updating   41s
es-multinode                        Delete               Running    42s

Check the pod status and roles:

kubectl get pods -l app.kubernetes.io/instance=es-multinode -n demo

Expected Output:

NAME                    READY   STATUS    RESTARTS   AGE
es-multinode-dit-0      3/3     Running   0          6m21s
es-multinode-dit-1      3/3     Running   0          6m21s
es-multinode-dit-2      3/3     Running   0          6m21s
es-multinode-master-0   3/3     Running   0          6m21s
es-multinode-master-1   3/3     Running   0          6m21s
es-multinode-master-2   3/3     Running   0          6m21s

Once the cluster status becomes Running, your Elasticsearch cluster is ready for use.

Decommission a Pod

Expected Workflow:

1. Replica specified in onlineInstancesToOffline is removed
2. Pod terminates gracefully
3. Cluster transitions from Updating to Running

To decommission a specific Pod (e.g., 'es-multinode-dit-1'), you can use one of the following methods:

apiVersion: operations.kubeblocks.io/v1alpha1
kind: OpsRequest
metadata:
  name: es-multinode-decommission-ops
  namespace: demo
spec:
  clusterName: es-multinode
  type: HorizontalScaling
  horizontalScaling:
  - componentName: dit
    scaleIn:
      onlineInstancesToOffline:
        - 'es-multinode-dit-1'  # Specifies the instance names that need to be taken offline

kubectl get ops es-multinode-decommission-ops -n demo -w

NAME                            TYPE                CLUSTER        STATUS    PROGRESS   AGE
es-multinode-decommission-ops   HorizontalScaling   es-multinode   Running   0/1        8s
es-multinode-decommission-ops   HorizontalScaling   es-multinode   Running   1/1        31s
es-multinode-decommission-ops   HorizontalScaling   es-multinode   Succeed   1/1        31s

apiVersion: apps.kubeblocks.io/v1
kind: Cluster
spec:
  componentSpecs:
    - name: dit
      replicas: 2       # explected replicas after decommission
      offlineInstances:
        - es-multinode-dit-1   # <----- Specify Pod to be decommissioned
 ...

Verify the Decommissioning

After applying the updated configuration, verify the remaining Pods in the cluster:

kubectl get pods -n demo -l app.kubernetes.io/instance=es-multinode,apps.kubeblocks.io/component-name=dit

Example Output:

NAME                 READY   STATUS    RESTARTS   AGE
es-multinode-dit-0   2/2     Running   0          24m
es-multinode-dit-2   2/2     Running   0          2m1s

Summary

Key takeaways:

• Traditional StatefulSets lack precise Pod removal control
• KubeBlocks enables targeted Pod decommissioning
• Two implementation methods: OpsRequest or Cluster API

This provides granular cluster management while maintaining availability.