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Redis Volume Expansion

This guide will show you how to use KubeDB Enterprise operator to expand the volume of a Redis.

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.
You must have a StorageClass that supports volume expansion.
Install KubeDB Community and Enterprise operator in your cluster following the steps here.
You should be familiar with the following KubeDB concepts:

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

$ kubectl create ns demo
namespace/demo created

Expand Volume of Redis

Here, we are going to deploy a Redis cluster using a supported version by KubeDB operator. Then we are going to apply RedisOpsRequest to expand its volume. The process of expanding Redis standalone is same as Redis cluster.

Prepare Redis Database

At first verify that your cluster has a storage class, that supports volume expansion. Let’s check,

$ kubectl get storageclass
NAME                  PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
standard (default)    rancher.io/local-path   Delete          WaitForFirstConsumer   false                  69s
topolvm-provisioner   topolvm.cybozu.com      Delete          WaitForFirstConsumer   true                   37s

We can see from the output the topolvm-provisioner storage class has ALLOWVOLUMEEXPANSION field as true. So, this storage class supports volume expansion. We will use this storage class. You can install topolvm from here.

Now, we are going to deploy a Redis database with in Cluster Mode version 6.2.5.

Deploy Redis

In this section, we are going to deploy a Redis Cluster with 1GB volume. Then, in the next section we will expand its volume to 2GB using RedisOpsRequest CRD. Below is the YAML of the Redis CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: Redis
metadata:
  name: sample-redis
  namespace: demo
spec:
  version: 6.2.5
  mode: Cluster
  cluster:
    master: 3
    replicas: 1
  storageType: Durable
  storage:
    storageClassName: "topolvm-provisioner"
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi
  terminationPolicy: Halt

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.04.10/docs/example/redis/volume-expansion/sample-redis.yaml
redis.kubedb.com/sample-redis created

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

$ kubectl get redis -n demo
NAME             VERSION   STATUS   AGE
sample-redis     6.2.5    Ready    5m4s

Let’s check volume size from statefulset, and from the persistent volume,

$ kubectl get sts -n demo sample-redis-shard0 -o json | jq '.spec.volumeClaimTemplates[].spec.resources.requests.storage'
"1Gi"

$ kubectl get pv -n demo
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                             STORAGECLASS              REASON   AGE
pvc-032f1355-1720-4d85-b1e5-b86427bc4662   1Gi        RWO            Delete           Bound    demo/data-sample-redis-shard0-1   topolvm-provisioner                2m49s
pvc-207ac9aa-2ba2-432b-ac00-8cc1cd46e20a   1Gi        RWO            Delete           Bound    demo/data-sample-redis-shard2-0   topolvm-provisioner                2m49s
pvc-20c946e4-4812-4dfc-a76e-4629bcd385dc   1Gi        RWO            Delete           Bound    demo/data-sample-redis-shard2-1   topolvm-provisioner                2m38s
pvc-69158d05-c715-4dd5-afee-2f5d196ba1f9   1Gi        RWO            Delete           Bound    demo/data-sample-redis-shard1-0   topolvm-provisioner                2m53s
pvc-aee29446-eff0-430e-95ff-ae853e73a244   1Gi        RWO            Delete           Bound    demo/data-sample-redis-shard1-1   topolvm-provisioner                2m41s
pvc-d37fbdf9-90bd-4b5e-b3b2-7e40156c13a8   1Gi        RWO            Delete           Bound    demo/data-sample-redis-shard0-0   topolvm-provisioner                2m56s

You can see the statefulset has 1GB storage, and the capacity of all the persistent volumes are also 1GB.

We are now ready to apply the RedisOpsRequest CR to expand the volume of this database.

Volume Expansion

Here, we are going to expand the volume of the Redis cluster.

Create RedisOpsRequest

In order to expand the volume of the database, we have to create a RedisOpsRequest CR with our desired volume size. Below is the YAML of the RedisOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: RedisOpsRequest
metadata:
  name: rd-online-volume-expansion
  namespace: demo
spec:
  type: VolumeExpansion  
  databaseRef:
    name: sample-redis
  volumeExpansion:   
    mode: "Online"
    redis: 2Gi

Here,

spec.databaseRef.name specifies that we are performing volume expansion operation on sample-redis database.
spec.type specifies that we are performing VolumeExpansion on our database.
spec.volumeExpansion.redis specifies the desired volume size.
spec.volumeExpansion.mode specifies the desired volume expansion mode (Online or Offline). Storageclass topolvm-provisioner supports Online volume expansion.

Note: If the Storageclass you are using doesn’t support Online Volume Expansion, Try offline volume expansion by using spec.volumeExpansion.mode:"Offline".

During Online VolumeExpansion KubeDB expands volume without pausing database object, it directly updates the underlying PVC. And for Offline volume expansion, the database is paused. The Pods are deleted and PVC is updated. Then the database Pods are recreated with updated PVC.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2023.04.10/docs/example/redis/volume-expansion/online-vol-expansion.yaml
redisopsrequest.ops.kubedb.com/rd-online-volume-expansion created

Verify Redis volume expanded successfully

If everything goes well, KubeDB Enterprise operator will update the volume size of Redis object and related StatefulSets and Persistent Volumes.

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

$ kubectl get redisopsrequest -n demo
NAME                         TYPE              STATUS       AGE
rd-online-volume-expansion   VolumeExpansion   Successful   96s

We can see from the above output that the RedisOpsRequest has succeeded.

Now, we are going to verify from the Statefulset, and the Persistent Volumes whether the volume of the database has expanded to meet the desired state, Let’s check,

$ kubectl get sts -n demo sample-redis-shard0 -o json | jq '.spec.volumeClaimTemplates[].spec.resources.requests.storage'
"2Gi"

$ kubectl get sts -n demo sample-redis-shard1 -o json | jq '.spec.volumeClaimTemplates[].spec.resources.requests.storage'
"2Gi"

$ kubectl get pv -n demo
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                             STORAGECLASS              REASON   AGE
pvc-032f1355-1720-4d85-b1e5-b86427bc4662   2Gi        RWO            Delete           Bound    demo/data-sample-redis-shard0-1   topolvm-provisioner                7m9s
pvc-207ac9aa-2ba2-432b-ac00-8cc1cd46e20a   2Gi        RWO            Delete           Bound    demo/data-sample-redis-shard2-0   topolvm-provisioner                7m9s
pvc-20c946e4-4812-4dfc-a76e-4629bcd385dc   2Gi        RWO            Delete           Bound    demo/data-sample-redis-shard2-1   topolvm-provisioner                7m8s
pvc-69158d05-c715-4dd5-afee-2f5d196ba1f9   2Gi        RWO            Delete           Bound    demo/data-sample-redis-shard1-0   topolvm-provisioner                7m3s
pvc-aee29446-eff0-430e-95ff-ae853e73a244   2Gi        RWO            Delete           Bound    demo/data-sample-redis-shard1-1   topolvm-provisioner                7m1s
pvc-d37fbdf9-90bd-4b5e-b3b2-7e40156c13a8   2Gi        RWO            Delete           Bound    demo/data-sample-redis-shard0-0   topolvm-provisioner                7m6s

The above output verifies that we have successfully expanded the volume of the Redis database.

Standalone Mode and Sentinel Mode

The volume expansion process is same for all the Redis modes. The RedisOpsRequest CR has the sample fields. The database needs to refer to a redis database in standalone or sentinel mode.

Cleaning Up

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

$ kubectl delete redis -n demo sample-redis
$ kubectl delete redisopsrequest -n demo rd-online-volume-expansion

$ kubectl patch -n demo rd/sample-redis -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
redis.kubedb.com/sample-redis patched

$ kubectl delete -n demo redis sample-redis
redis.kubedb.com "sample-redis" deleted

$ kubectl delete -n demo redisopsrequest rd-online-volume-expansion
redisopsrequest.ops.kubedb.com "rd-online-volume-expansion" deleted

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