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Storage Autoscaling of a Redis Standalone Database

This guide will show you how to use KubeDB to autoscale the storage of a Redis standalone 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.
Install KubeDB Provisioner, Ops-manager and Autoscaler operator in your cluster following the steps here.
Install Metrics Server from here
Install Prometheus from here
You must have a StorageClass that supports volume expansion.
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

Note: YAML files used in this tutorial are stored in docs/examples/redis directory of kubedb/docs repository.

Storage Autoscaling of Standalone 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                  9h
topolvm-provisioner   topolvm.cybozu.com      Delete          WaitForFirstConsumer   true                   9h

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

Now, we are going to deploy a Redis standalone using a supported version by KubeDB operator. Then we are going to apply RedisAutoscaler to set up autoscaling.

Deploy Redis standalone

If you want to autoscale Redis in Cluster or Sentinel mode, just deploy a Redis database in respective Mode and rest of the steps are same.

In this section, we are going to deploy a Redis standalone database with version 6.2.5. Then, in the next section we will set up autoscaling for this database using RedisAutoscaler CRD. Below is the YAML of the Redis CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: Redis
metadata:
  name: rd-standalone
  namespace: demo
spec:
  version: "6.2.5"
  storageType: Durable
  storage:
    storageClassName: topolvm-provisioner
    resources:
      requests:
        storage: 1Gi
  terminationPolicy: WipeOut

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.04.10/docs/examples/redis/autoscaling/storage/rd-standalone.yaml
redis.kubedb.com/rd-standalone created

Now, wait until rd-standalone has status Ready. i.e,

$ kubectl get rd -n demo
NAME            VERSION    STATUS    AGE
rd-standalone   6.2.5      Ready     2m53s

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

$ kubectl get sts -n demo rd-standalone -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-cf469ed8-a89a-49ca-bf7c-8c76b7889428   1Gi        RWO            Delete           Bound    demo/datadir-rd-standalone-0   topolvm-provisioner            7m41s

You can see the statefulset has 1GB storage, and the capacity of the persistent volume is also 1GB.

We are now ready to apply the RedisAutoscaler CRO to set up storage autoscaling for this database.

Storage Autoscaling

Here, we are going to set up storage autoscaling using a RedisAutoscaler Object.

Create RedisAutoscaler Object

In order to set up vertical autoscaling for this standalone database, we have to create a RedisAutoscaler CRO with our desired configuration. Below is the YAML of the RedisAutoscaler object that we are going to create,

apiVersion: autoscaling.kubedb.com/v1alpha1
kind: RedisAutoscaler
metadata:
  name: rd-as
  namespace: demo
spec:
  databaseRef:
    name: rd-standalone
  storage:
    standalone:
      trigger: "On"
      usageThreshold: 60
      scalingThreshold: 50

If you want to autoscale Redis in Cluster mode, the field in spec.storage should be cluster and for sentinel it should be sentinel. The subfields are same inside spec.storage.standalone, spec.storage.cluster and spec.storage.sentinel

Here,

spec.databaseRef.name specifies that we are performing vertical scaling operation on rd-standalone database.
spec.storage.standalone.trigger specifies that storage autoscaling is enabled for this database.
spec.storage.standalone.usageThreshold specifies storage usage threshold, if storage usage exceeds 60% then storage autoscaling will be triggered.
spec.storage.standalone.scalingThreshold specifies the scaling threshold. Storage will be scaled to 50% of the current amount.
It has another field spec.storage.replicaSet.expansionMode to set the opsRequest volumeExpansionMode, which support two values: Online & Offline. Default value is Online.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2023.04.10/docs/examples/redis/autoscaling/storage/rd-as.yaml
redisautoscaler.autoscaling.kubedb.com/rd-as created

Storage Autoscaling is set up successfully

Let’s check that the redisautoscaler resource is created successfully,

$ kubectl get redisautoscaler -n demo
NAME    AGE
rd-as   102s

$ kubectl describe redisautoscaler rd-as -n demo
Name:         rd-as
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  autoscaling.kubedb.com/v1alpha1
Kind:         RedisAutoscaler
Metadata:
  Creation Timestamp:  2023-02-09T11:02:26Z
  Generation:          1
  Managed Fields:
    API Version:  autoscaling.kubedb.com/v1alpha1
    Fields Type:  FieldsV1
    fieldsV1:
      f:metadata:
        f:annotations:
          .:
          f:kubectl.kubernetes.io/last-applied-configuration:
      f:spec:
        .:
        f:databaseRef:
          .:
          f:name:
        f:storage:
          .:
          f:standalone:
            .:
            f:scalingThreshold:
            f:trigger:
            f:usageThreshold:
    Manager:         kubectl-client-side-apply
    Operation:       Update
    Time:            2023-02-09T11:02:26Z
  Resource Version:  134423
  Self Link:         /apis/autoscaling.kubedb.com/v1alpha1/namespaces/demo/redisautoscalers/rd-as
  UID:               999a2dc9-7eb7-4ed2-9e90-d3f8b21c091a
Spec:
  Database Ref:
    Name:  rd-standalone
  Storage:
    Standalone:
      Scaling Threshold:  50
      Trigger:            On
      Usage Threshold:    60
Events:                   <none>

So, the redisautoscaler resource is created successfully.

Now, for this demo, we are going to manually fill up the persistent volume to exceed the usageThreshold using dd command to see if storage autoscaling is working or not.

Lets exec into the database pod and fill the database volume using the following commands:

$ kubectl exec -it -n demo rd-standalone-0 -- bash
root@rd-standalone-0:/# df -h /data
Filesystem                                         Size  Used Avail Use% Mounted on
/dev/topolvm/1df4ee9e-b900-4c0f-9d2c-8493fb30bdc0 1014M  334M  681M  33% /data/db
root@rd-standalone-0:/# dd if=/dev/zero of=/data/file.img bs=500M count=1
1+0 records in
1+0 records out
524288000 bytes (524 MB, 500 MiB) copied, 0.359202 s, 1.5 GB/s
root@rd-standalone-0:/# df -h /data
Filesystem                                         Size  Used Avail Use% Mounted on
/dev/topolvm/1df4ee9e-b900-4c0f-9d2c-8493fb30bdc0 1014M  835M  180M  83% /data/db

So, from the above output we can see that the storage usage is 84%, which exceeded the usageThreshold 60%.

Let’s watch the redisopsrequest in the demo namespace to see if any redisopsrequest object is created. After some time you’ll see that a redisopsrequest of type VolumeExpansion will be created based on the scalingThreshold.

$ watch kubectl get redisopsrequest -n demo
Every 2.0s: kubectl get redisopsrequest -n demo
NAME                         TYPE              STATUS        AGE
rdops-rd-standalone-p27c11   VolumeExpansion   Progressing   26s

Let’s wait for the ops request to become successful.

$ watch kubectl get redisopsrequest -n demo
Every 2.0s: kubectl get redisopsrequest -n demo
NAME                         TYPE              STATUS        AGE
rdops-rd-standalone-p27c11   VolumeExpansion   Successful    73s

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

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

$ kubectl get sts -n demo rd-standalone -o json | jq '.spec.volumeClaimTemplates[].spec.resources.requests.storage'
"1594884096"
$ kubectl get pv -n demo
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                          STORAGECLASS          REASON   AGE
pvc-cf469ed8-a89a-49ca-bf7c-8c76b7889428   2Gi        RWO            Delete           Bound    demo/datadir-rd-standalone-0   topolvm-provisioner            26m

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

Cleaning Up

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

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

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

$ kubectl delete redisautoscaler -n demo rd-as
redisautoscaler.autoscaling.kubedb.com "rd-as" deleted

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