Decommission a Specific Pod in KubeBlocks-Managed RabbitMQ Clusters

This guide explains how to decommission (take offline) specific Pods in RabbitMQ 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 RabbitMQ Cluster

KubeBlocks uses a declarative approach for managing RabbitMQ Clusters. Below is an example configuration for deploying a RabbitMQ Cluster with 3 replicas.

Apply the following YAML configuration to deploy the cluster:

apiVersion: apps.kubeblocks.io/v1
kind: Cluster
metadata:
  name: rabbitmq-cluster
  namespace: demo
spec:
  terminationPolicy: Delete
  clusterDef: rabbitmq
  topology: clustermode
  componentSpecs:
    - name: rabbitmq
      serviceVersion: 3.13.7
      replicas: 3
      resources:
        limits:
          cpu: "0.5"
          memory: "0.5Gi"
        requests:
          cpu: "0.5"
          memory: "0.5Gi"
      volumeClaimTemplates:
        - name: data
          spec:
            storageClassName: ""
            accessModes:
              - ReadWriteOnce
            resources:
              requests:
                storage: 20Gi

Verifying the Deployment

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

kubectl get cluster rabbitmq-cluster -n demo -w

Expected Output:

kubectl get cluster rabbitmq-cluster -n demo
NAME               CLUSTER-DEFINITION   TERMINATION-POLICY   STATUS     AGE
rabbitmq-cluster   rabbitmq             Delete               Creating   15s
rabbitmq-cluster   rabbitmq             Delete               Running    83s

Check the pod status and roles:

kubectl get pods -l app.kubernetes.io/instance=rabbitmq-cluster -n demo

Expected Output:

NAME                          READY   STATUS    RESTARTS   AGE
rabbitmq-cluster-rabbitmq-0   2/2     Running   0          106s
rabbitmq-cluster-rabbitmq-1   2/2     Running   0          82s
rabbitmq-cluster-rabbitmq-2   2/2     Running   0          47s

Once the cluster status becomes Running, your RabbitMQ 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

Before decommissioning a specific pod from a component, make sure this component has more than one replicas. If not, please scale out the component ahead.

E.g. you can patch the cluster CR with command, to declare there are 3 replicas in component querynode.

kubectl patch cluster milvus-cluster -n demo --type='json' -p='[
  {
    "op": "replace",
    "path": "/spec/componentSpecs/2/replicas",
    "value": 3
  }
]'

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

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

kubectl get ops rabbitmq-cluster-decommission-ops -n demo -w

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

apiVersion: apps.kubeblocks.io/v1
kind: Cluster
spec:
  componentSpecs:
    - name: rabbitmq
      replicas: 2       # explected replicas after decommission
      offlineInstances:
        - rabbitmq-cluster-rabbitmq-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=rabbitmq-cluster

Example Output:

NAME                          READY   STATUS    RESTARTS   AGE
rabbitmq-cluster-rabbitmq-0   2/2     Running   0          25m
rabbitmq-cluster-rabbitmq-2   2/2     Running   0          24m

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.