Decommission a Specific Pod in KubeBlocks-Managed Qdrant Clusters

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

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

Apply the following YAML configuration to deploy the cluster:

apiVersion: apps.kubeblocks.io/v1
kind: Cluster
metadata:
  name: qdrant-cluster
  namespace: demo
spec:
  terminationPolicy: Delete
  clusterDef: qdrant
  topology: cluster
  componentSpecs:
    - name: qdrant
      serviceVersion: 1.10.0
      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 qdrant-cluster -n demo -w

Expected Output:

kubectl get cluster qdrant-cluster -n demo
NAME             CLUSTER-DEFINITION   TERMINATION-POLICY   STATUS     AGE
qdrant-cluster   qdrant              Delete               Creating   49s
qdrant-cluster   qdrant              Delete               Running    62s

Check the pod status and roles:

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

Expected Output:

NAME                      READY   STATUS    RESTARTS   AGE
qdrant-cluster-qdrant-0   2/2     Running   0          1m43s
qdrant-cluster-qdrant-1   2/2     Running   0          1m28s
qdrant-cluster-qdrant-2   2/2     Running   0          1m14s

Once the cluster status becomes Running, your Qdrant 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., 'qdrant-cluster-qdrant-1'), you can use one of the following methods:

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

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

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

apiVersion: apps.kubeblocks.io/v1
kind: Cluster
spec:
  componentSpecs:
    - name: qdrant
      replicas: 1       # explected replicas after decommission
      offlineInstances:
        - qdrant-cluster-qdrant-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=qdrant-cluster

Example Output:

NAME                      READY   STATUS    RESTARTS   AGE
qdrant-cluster-qdrant-0   2/2     Running   0          25m
qdrant-cluster-qdrant-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.