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Horizontal Scale of Redis Sentinel

This guide will give an overview on how KubeDB Ops-manager operator scales up or down Redis database and RedisSentinel instance.

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:

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.

Prepare Redis Sentinel Database

Now, we are going to deploy a RedisSentinel instance with version 6.2.7 and a Redis database with version 6.2.5. Then, in the next section we are going to apply horizontal scaling on the sentinel and the database using RedisSentinelOpsRequest and RedisOpsRequest CRD.

Deploy RedisSentinel :

In this section, we are going to deploy a RedisSentinel instance. Below is the YAML of the RedisSentinel CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: RedisSentinel
metadata:
  name: sen-sample
  namespace: demo
spec:
  version: 6.2.7
  replicas: 5
  storageType: Durable
  storage:
    resources:
      requests:
        storage: 1Gi
    storageClassName: "standard"
    accessModes:
      - ReadWriteOnce
  terminationPolicy: DoNotTerminate

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.12.11/docs/examples/redis/scaling/horizontal-scaling/sentinel.yaml
redissentinel.kubedb.com/sen-sample created

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

$ kubectl get redissentinel -n demo
NAME         VERSION   STATUS   AGE
sen-sample   6.2.7     Ready    5m20s

Let’s check the number of replicas this sentinel has from the RedisSentinel object

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

Deploy Redis :

In this section, we are going to deploy a Redis instance which will be monitored by previously created sen-sample. Below is the YAML of the Redis CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: Redis
metadata:
  name: rd-sample
  namespace: demo
spec:
  version: 6.2.5
  replicas: 3
  sentinelRef:
    name: sen-sample
    namespace: demo
  mode: Sentinel
  storageType: Durable
  storage:
    resources:
      requests:
        storage: 1Gi
    storageClassName: "standard"
    accessModes:
      - ReadWriteOnce
  terminationPolicy: DoNotTerminate

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.12.11/docs/examples/redis/scaling/horizontal-scaling/rd-sentinel.yaml
redis.kubedb.com/rd-sample created

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

$ kubectl get redis -n demo
NAME        VERSION   STATUS   AGE
rd-sample   6.2.5     Ready    2m11s

Let’s check the Pod containers resources,

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

Now let’s connect to redis with redis-cli to check the replication configuration

$ kubectl exec -it -n demo rd-sample-0 -c redis -- redis-cli info replication
# Replication
role:master
connected_slaves:2
slave0:ip=rd-sample-1.rd-sample-pods.demo.svc,port=6379,state=online,offset=35478,lag=0
slave1:ip=rd-sample-2.rd-sample-pods.demo.svc,port=6379,state=online,offset=35478,lag=0
master_failover_state:no-failover
master_replid:4ac5cc7292e84c6d1b69d3732869557f2854db2d
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:35492
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:35492

Additionally, the sentinel monitoring can be checked with following command :

kubectl exec -it -n demo sen-sample-0 -c redissentinel -- redis-cli -p 26379 sentinel masters

We are now ready to apply the RedisSentinelOpsRequest CR to horizontal scale on sentinel and RedisOpsRequest CR to horizontal scale database.

Horizontal Scale RedisSentinel

Here, we are going to scale down the replicas count of the sentinel to meet the desired resources after scaling.

Create RedisSentinelOpsRequest:

In order to scale the replicas of the sentinel, we have to create a RedisSentinelOpsRequest CR with our desired number of replicas. Below is the YAML of the RedisSentinelOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: RedisSentinelOpsRequest
metadata:
  name: sen-ops-horizontal
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: sen-sample
  horizontalScaling:
    replicas: 3

Here,

spec.databaseRef.name specifies that we are performing operation on sen-sample RedisSentinel instance.
spec.type specifies that we are going to perform HorizontalScaling on our database.
spec.horizontalScaling.replicas specifies the desired number of replicas after scaling.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2023.12.11/docs/examples/redis/scaling/horizontal-scaling/horizontal-sentinel.yaml
redissentinelopsrequest.ops.kubedb.com/sen-ops-horizontal created

Verify RedisSentinel replicas updated successfully :

If everything goes well, KubeDB Enterprise operator will scale down the replicas of RedisSentinel object.

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

$ watch kubectl get redissentinelopsrequest -n demo
Every 2.0s: kubectl get redissentinelopsrequest -n demo
NAME                 TYPE              STATUS       AGE
sen-ops-horizontal   HorizontalScaling   Successful   5m27s

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

Let’s check the number of master and replicas this database has from the RedisSentinel object

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

The above output verifies that we have successfully scaled up the resources of the sentinel instance.

Horizontal Scale Redis

Here, we are going to update the resources of the redis database to meet the desired resources after scaling.

Create RedisOpsRequest:

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

apiVersion: ops.kubedb.com/v1alpha1
kind: RedisOpsRequest
metadata:
  name: rd-ops-horizontal
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: rd-sample
  horizontalScaling:
    replicas: 5

Here,

spec.databaseRef.name specifies that we are performing operation on rd-sample Redis database.
spec.type specifies that we are going to perform HorizontalScaling on our database.
spec.horizontalScaling.replicas specifies the desired number of replicas after scaling.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2023.12.11/docs/examples/redis/scaling/horizontal-scaling//horizontal-redis-sentinel.yaml
redisopsrequest.ops.kubedb.com/rd-ops-horizontal created

Verify Redis resources updated successfully :

If everything goes well, KubeDB Enterprise operator will scale up the replicas of Redis object.

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

$ watch kubectl get redisopsrequest -n demo
NAME                TYPE                STATUS       AGE
rd-ops-horizontal   HorizontalScaling   Successful   4m4s

We can see from the above output that the RedisOpsRequest has succeeded. Now, we are going to verify if the number of replicas the redis sentinel has updated to meet up the desired state, Let’s check,

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

Now let’s connect to redis with redis-cli to check the replication configuration

$ kubectl exec -it -n demo rd-sample-0 -c redis -- redis-cli info replication
# Replication
role:master
connected_slaves:4
slave0:ip=rd-sample-1.rd-sample-pods.demo.svc,port=6379,state=online,offset=325651,lag=1
slave1:ip=rd-sample-2.rd-sample-pods.demo.svc,port=6379,state=online,offset=325651,lag=1
slave2:ip=rd-sample-3.rd-sample-pods.demo.svc,port=6379,state=online,offset=325651,lag=1
slave3:ip=rd-sample-4.rd-sample-pods.demo.svc,port=6379,state=online,offset=325651,lag=1
master_failover_state:no-failover
master_replid:4871c4756eebbadc7f2c56a4dd1dff11e20a04ba
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:325651
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:325651

The above output verifies that we have successfully scaled up the resources of the redis database. There are 1 master and 4 connected slaves. So, the Ops Request scaled up the replicas to 5.

Additionally, the sentinel monitoring can be checked with following command :

kubectl exec -it -n demo sen-sample-0 -c redissentinel -- redis-cli -p 26379 sentinel masters

Cleaning Up

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

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

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

$ kubectl delete -n demo redisopsrequest rd-ops-horizontal 
redisopsrequest.ops.kubedb.com "rd-ops-horizontal" deleted

# Delete RedisSentinel and RedisSentinelOpsRequest
$ kubectl patch -n demo redissentinel/sen-sample -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
redissentinel.kubedb.com/sen-sample patched

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

$ kubectl delete -n demo redissentinelopsrequests sen-ops-horizontal 
redissentinelopsrequest.ops.kubedb.com "sen-ops-horizontal" deleted

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