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Horizontal Scale MariaDB

This guide will show you how to use KubeDB Enterprise operator to scale the cluster of a MariaDB 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:

  • MariaDB
  • MariaDB Cluster
  • MariaDBOpsRequest
  • 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 MariaDB cluster using a supported version by KubeDB operator. Then we are going to apply horizontal scaling on it.

Prepare MariaDB Cluster Database

Now, we are going to deploy a MariaDB cluster with version 10.5.8.

Deploy MariaDB Cluster

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

apiVersion: kubedb.com/v1alpha2
kind: MariaDB
metadata:
  name: sample-mariadb
  namespace: demo
spec:
  version: "10.5.8"
  replicas: 3
  storageType: Durable
  storage:
    storageClassName: "standard"
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi
  terminationPolicy: WipeOut

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2022.05.24/docs/guides/mariadb/scaling/horizontal-scaling/cluster/example/sample-mariadb.yaml
mariadb.kubedb.com/sample-mariadb created

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

$ kubectl get mariadb -n demo
NAME             VERSION   STATUS   AGE
sample-mariadb   10.5.8    Ready    2m36s

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

$ kubectl get mariadb -n demo sample-mariadb -o json | jq '.spec.replicas'
3
$ kubectl get sts -n demo sample-mariadb -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 mariadb command by execing into a replica.

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

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

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

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

$  kubectl exec -it -n demo sample-mariadb-0 -c mariadb -- bash
root@sample-mariadb-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 MariaDBOpsRequest 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 MariaDBOpsRequest

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

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

Here,

• spec.databaseRef.name specifies that we are performing horizontal scaling operation on sample-mariadb 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 MariaDBOpsRequest CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2022.05.24/docs/guides/mariadb/scaling/horizontal-scaling/cluster/example/mdops-upscale.yaml
mariadbopsrequest.ops.kubedb.com/mdops-scale-horizontal-up created

Verify Cluster replicas scaled up successfully

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

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

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

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

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

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

$ $  kubectl exec -it -n demo sample-mariadb-0 -c mariadb -- bash
root@sample-mariadb-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 MariaDB 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 MariaDBOpsRequest

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

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

Here,

• spec.databaseRef.name specifies that we are performing horizontal scaling down operation on sample-mariadb 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 MariaDBOpsRequest CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2022.05.24/docs/guides/mariadb/scaling/horizontal-scaling/cluster/example/mdops-downscale.yaml
mariadbopsrequest.ops.kubedb.com/mdops-scale-horizontal-down created

Verify Cluster replicas scaled down successfully

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

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

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

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

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

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

$ $  kubectl exec -it -n demo sample-mariadb-0 -c mariadb -- bash
root@sample-mariadb-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 MariaDB replicaset.

Cleaning Up

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

$ kubectl delete mariadb -n demo sample-mariadb
$ kubectl delete mariadbopsrequest -n demo  mdops-scale-horizontal-up mdops-scale-horizontal-down