Configuring a MySQL Cluster with Gradual Rolling Update in KubeBlocks

This guide demonstrates how to configure gradual rolling updates for MySQL clusters in KubeBlocks using the rollingUpdate strategy. Gradual rolling updates allow you to control the number of Pods updated at a time, ensuring minimal disruption during updates. Key Parameters:

• rollingUpdate.replicas: Specifies the number of instances to update during each step of the rolling update. The remaining instances stay unaffected.
  • The value can be an absolute number (e.g., 5) or a percentage of desired instances (e.g., 10%).
  • Absolute numbers are calculated by rounding up percentages.
  • The default is the total number of replicas, meaning all instances are updated.
• rollingUpdate.maxUnavailable: Limits the maximum number of instances that can be unavailable during the update.
  • The value can also be an absolute number (e.g., 5) or a percentage (e.g., 10%).
  • This value cannot be 0. The default is 1.

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 MySQL Semi-Synchronous Cluster

Deploy a 2-node MySQL cluster with semi-synchronous replication (1 primary, 1 secondary) using the following YAML configuration:

kubectl apply -f - <<EOF
apiVersion: apps.kubeblocks.io/v1
kind: Cluster
metadata:
  name: example-mysql-cluster
  namespace: demo
spec:
  clusterDef: mysql
  topology: semisync
  terminationPolicy: Delete
  componentSpecs:
    - name: mysql
      serviceVersion: 8.0.35
      replicas: 2
      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
EOF

Verifying the Deployment

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

kubectl get cluster example-mysql-cluster -n demo -w

Example Output:

NAME                     CLUSTER-DEFINITION   TERMINATION-POLICY   STATUS    AGE
example-mysql-cluster   mysql                Delete               Creating   6s
example-mysql-cluster   mysql                Delete               Running    3m47s

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

Performing Gradual Rolling Updates

This section demonstrates how to gradually update Pods in the MySQL cluster.

Step 1. Trigger Resource Update

Update the resource requests and limits for the MySQL cluster while setting rollingUpdate.replicas to 1. This ensures only one Pod gets updated at a time.

kubectl patch cluster example-mysql-cluster -n demo --type='json' -p='[
  {
    "op": "add",
    "path": "/spec/componentSpecs/0/instanceUpdateStrategy",
    "value": {
      "rollingUpdate": {
        "replicas": 1
      }
    }
  },
  {
    "op": "replace",
    "path": "/spec/componentSpecs/0/resources/limits/cpu",
    "value": "1.0"
  },
  {
    "op": "replace",
    "path": "/spec/componentSpecs/0/resources/limits/memory",
    "value": "1.0Gi"
  },
  {
    "op": "replace",
    "path": "/spec/componentSpecs/0/resources/requests/cpu",
    "value": "1.0"
  },
  {
    "op": "replace",
    "path": "/spec/componentSpecs/0/resources/requests/memory",
    "value": "1.0Gi"
  }
]'

Step 2. Observe the Update Process

Check the cluster status after applying the patch:

kubectl get cluster example-mysql-cluster -n demo

Example Output:

NAME                    CLUSTER-DEFINITION   TERMINATION-POLICY   STATUS     AGE
example-mysql-cluster   mysql                Delete               Updating   5m57s

The cluster status shows Updating, and one Pod will restart to apply the changes.

Monitor the Pod update process:

kubectl get pods -n demo -w

Example Output:

NAME                            READY   STATUS     RESTARTS   AGE
example-mysql-cluster-mysql-0   4/4     Running    0          3m3s
example-mysql-cluster-mysql-1   0/4     Init:1/6   0          10s
example-mysql-cluster-mysql-1   0/4     Init:2/6   0          24s
example-mysql-cluster-mysql-1   0/4     Init:3/6   0          25s
example-mysql-cluster-mysql-1   0/4     Init:4/6   0          26s
example-mysql-cluster-mysql-1   0/4     Init:5/6   0          27s
example-mysql-cluster-mysql-1   0/4     PodInitializing   0          28s
example-mysql-cluster-mysql-1   3/4     Running           0          29s
example-mysql-cluster-mysql-1   4/4     Running           0          34s

Step 3. Gradually Update the Remaining Pods

After the first Pod is updated, increase rollingUpdate.replicas to 2 to update the next Pod.

kubectl patch cluster example-mysql-cluster -n demo --type='json' -p='[
  {
    "op": "replace",
    "path": "/spec/componentSpecs/0/instanceUpdateStrategy/rollingUpdate/replicas",
    "value": 2
  }
]'

Monitor the rest pod is updated:

kubectl get pods -n demo  -w

Example Output:

example-mysql-cluster-mysql-0   4/4     Terminating       0          8m7s
example-mysql-cluster-mysql-0   0/4     Pending           0          0s
example-mysql-cluster-mysql-0   0/4     Init:0/6          0          0s
example-mysql-cluster-mysql-0   0/4     Init:1/6          0          7s
example-mysql-cluster-mysql-0   0/4     Init:1/6          0          8s
example-mysql-cluster-mysql-0   0/4     Init:2/6          0          20s
example-mysql-cluster-mysql-0   0/4     Init:3/6          0          21s
example-mysql-cluster-mysql-0   0/4     Init:4/6          0          22s
example-mysql-cluster-mysql-0   0/4     Init:5/6          0          23s
example-mysql-cluster-mysql-0   0/4     PodInitializing   0          24s
example-mysql-cluster-mysql-0   3/4     Running           0          25s
example-mysql-cluster-mysql-0   4/4     Running           0          26s

Once all Pods are running, the cluster status will update to 'Running':

kubectl get cluster example-mysql-cluster -n demo -w

Example Output:

NAME                    CLUSTER-DEFINITION   TERMINATION-POLICY   STATUS    AGE
example-mysql-cluster   mysql                Delete               Running   9m26s

Cleanup

To remove all created resources, delete the MySQL cluster along with its namespace:

kubectl delete cluster example-mysql-cluster -n demo
kubectl delete ns demo

Summary

In this guide, we demonstrated how to configure and perform gradual rolling updates for a MySQL cluster in KubeBlocks. By customizing the rollingUpdate.replicas parameter, you can control the number of Pods updated at a time, ensuring a seamless update process with minimal disruption to your workload.