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Horizontal Scale PerconaXtraDB

This guide will show you how to use KubeDB Enterprise operator to scale the cluster of a PerconaXtraDB database.

Before You Begin

• At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using kind.

• Install KubeDB Community and Enterprise operator in your cluster following the steps here.

• You should be familiar with the following KubeDB concepts:

  • PerconaXtraDB
  • PerconaXtraDB Cluster
  • PerconaXtraDBOpsRequest
  • Horizontal Scaling Overview

To keep everything isolated, we are going to use a separate namespace called demo throughout this tutorial.

$ kubectl create ns demo
namespace/demo created

Apply Horizontal Scaling on Cluster

Here, we are going to deploy a PerconaXtraDB cluster using a supported version by KubeDB operator. Then we are going to apply horizontal scaling on it.

Prepare PerconaXtraDB Cluster Database

Now, we are going to deploy a PerconaXtraDB cluster with version 8.0.26.

Deploy PerconaXtraDB Cluster

In this section, we are going to deploy a PerconaXtraDB cluster. Then, in the next section we will scale the database using PerconaXtraDBOpsRequest CRD. Below is the YAML of the PerconaXtraDB CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: PerconaXtraDB
metadata:
  name: sample-pxc
  namespace: demo
spec:
  version: "8.0.26"
  replicas: 3
  storageType: Durable
  storage:
    storageClassName: "standard"
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi
  terminationPolicy: WipeOut

Let’s create the PerconaXtraDB CR we have shown above,

$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.01.17/docs/guides/percona-xtradb/scaling/horizontal-scaling/cluster/example/sample-pxc.yaml
perconaxtradb.kubedb.com/sample-pxc created

Now, wait until sample-pxc has status Ready. i.e,

$ kubectl get perconaxtradb -n demo
NAME             VERSION   STATUS   AGE
sample-pxc       8.0.26    Ready    2m36s

Let’s check the number of replicas this database has from the PerconaXtraDB object, number of pods the statefulset have,

$ kubectl get perconaxtradb -n demo sample-pxc -o json | jq '.spec.replicas'
3
$ kubectl get sts -n demo sample-pxc -o json | jq '.spec.replicas'
3

We can see from both command that the database has 3 replicas in the cluster.

Also, we can verify the replicas of the replicaset from an internal perconaxtradb command by execing into a replica.

First we need to get the username and password to connect to a perconaxtradb instance,

$ kubectl get secrets -n demo sample-pxc-auth -o jsonpath='{.data.\username}' | base64 -d
root

$ kubectl get secrets -n demo sample-pxc-auth -o jsonpath='{.data.\password}' | base64 -d
nrKuxni0wDSMrgwy

Now let’s connect to a perconaxtradb instance and run a perconaxtradb internal command to check the number of replicas,

$  kubectl exec -it -n demo sample-pxc-0 -c perconaxtradb -- bash
root@sample-pxc-0:/ mysql -uroot -p$MYSQL_ROOT_PASSWORD -e "show status like 'wsrep_cluster_size';"
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| wsrep_cluster_size | 3     |
+--------------------+-------+

We can see from the above output that the cluster has 3 nodes.

We are now ready to apply the PerconaXtraDBOpsRequest CR to scale this database.

Scale Up Replicas

Here, we are going to scale up the replicas of the replicaset to meet the desired number of replicas after scaling.

Create PerconaXtraDBOpsRequest

In order to scale up the replicas of the replicaset of the database, we have to create a PerconaXtraDBOpsRequest CR with our desired replicas. Below is the YAML of the PerconaXtraDBOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: PerconaXtraDBOpsRequest
metadata:
  name: pxops-scale-horizontal-up
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: sample-pxc
  horizontalScaling:
    member : 5

Here,

• spec.databaseRef.name specifies that we are performing horizontal scaling operation on sample-pxc database.
• spec.type specifies that we are performing HorizontalScaling on our database.
• spec.horizontalScaling.member specifies the desired replicas after scaling.

Let’s create the PerconaXtraDBOpsRequest CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2023.01.17/docs/guides/percona-xtradb/scaling/horizontal-scaling/cluster/example/pxops-upscale.yaml
perconaxtradbopsrequest.ops.kubedb.com/pxops-scale-horizontal-up created

Verify Cluster replicas scaled up successfully

If everything goes well, KubeDB Enterprise operator will update the replicas of PerconaXtraDB object and related StatefulSets and Pods.

Let’s wait for PerconaXtraDBOpsRequest to be Successful. Run the following command to watch PerconaXtraDBOpsRequest CR,

$ watch kubectl get perconaxtradbopsrequest -n demo
Every 2.0s: kubectl get perconaxtradbopsrequest -n demo
NAME                        TYPE                STATUS       AGE
pxps-scale-horizontal    HorizontalScaling    Successful     106s

We can see from the above output that the PerconaXtraDBOpsRequest has succeeded. Now, we are going to verify the number of replicas this database has from the PerconaXtraDB object, number of pods the statefulset have,

$ kubectl get perconaxtradb -n demo sample-pxc -o json | jq '.spec.replicas'
5
$ kubectl get sts -n demo sample-pxc -o json | jq '.spec.replicas'
5

Now let’s connect to a perconaxtradb instance and run a perconaxtradb internal command to check the number of replicas,

$ $  kubectl exec -it -n demo sample-pxc-0 -c perconaxtradb -- bash
root@sample-pxc-0:/ mysql -uroot -p$MYSQL_ROOT_PASSWORD -e "show status like 'wsrep_cluster_size';"
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| wsrep_cluster_size | 5     |
+--------------------+-------+

From all the above outputs we can see that the replicas of the cluster is 5. That means we have successfully scaled up the replicas of the PerconaXtraDB replicaset.

Scale Down Replicas

Here, we are going to scale down the replicas of the cluster to meet the desired number of replicas after scaling.

Create PerconaXtraDBOpsRequest

In order to scale down the cluster of the database, we have to create a PerconaXtraDBOpsRequest CR with our desired replicas. Below is the YAML of the PerconaXtraDBOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: PerconaXtraDBOpsRequest
metadata:
  name: pxops-scale-horizontal-down
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: sample-pxc
  horizontalScaling:
    member : 3

Here,

• spec.databaseRef.name specifies that we are performing horizontal scaling down operation on sample-pxc database.
• spec.type specifies that we are performing HorizontalScaling on our database.
• spec.horizontalScaling.replicas specifies the desired replicas after scaling.

Let’s create the PerconaXtraDBOpsRequest CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2023.01.17/docs/guides/percona-xtradb/scaling/horizontal-scaling/cluster/example/pxops-downscale.yaml
perconaxtradbopsrequest.ops.kubedb.com/pxops-scale-horizontal-down created

Verify Cluster replicas scaled down successfully

If everything goes well, KubeDB Enterprise operator will update the replicas of PerconaXtraDB object and related StatefulSets and Pods.

Let’s wait for PerconaXtraDBOpsRequest to be Successful. Run the following command to watch PerconaXtraDBOpsRequest CR,

$ watch kubectl get perconaxtradbopsrequest -n demo
Every 2.0s: kubectl get perconaxtradbopsrequest -n demo
NAME                          TYPE                STATUS       AGE
mops-hscale-down-replicaset   HorizontalScaling   Successful   2m32s

We can see from the above output that the PerconaXtraDBOpsRequest has succeeded. Now, we are going to verify the number of replicas this database has from the PerconaXtraDB object, number of pods the statefulset have,

$ kubectl get perconaxtradb -n demo sample-pxc -o json | jq '.spec.replicas' 
3
$ kubectl get sts -n demo sample-pxc -o json | jq '.spec.replicas'
3

Now let’s connect to a perconaxtradb instance and run a perconaxtradb internal command to check the number of replicas,

$ $  kubectl exec -it -n demo sample-pxc-0 -c perconaxtradb -- bash
root@sample-pxc-0:/ mysql -uroot -p$MYSQL_ROOT_PASSWORD -e "show status like 'wsrep_cluster_size';"
+--------------------+-------+
| Variable_name      | Value |
+--------------------+-------+
| wsrep_cluster_size | 5     |
+--------------------+-------+

From all the above outputs we can see that the replicas of the cluster is 5. That means we have successfully scaled down the replicas of the PerconaXtraDB replicaset.

Cleaning Up

To clean up the Kubernetes resources created by this tutorial, run:

$ kubectl delete perconaxtradb -n demo sample-pxc
$ kubectl delete perconaxtradbopsrequest -n demo  pxops-scale-horizontal-up pxops-scale-horizontal-down