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Replace Sentinel
This guide will show you how to use KubeDB Enterprise operator to replace Sentinel instance of Redis Database.
Before You Begin
At first, you need to have a Kubernetes cluster, and the
kubectlcommand-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
KubeDBCommunity and Enterprise operator in your cluster following the steps here.You should be familiar with the following
KubeDBconcepts:
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.
Apply ReplaceSentinel
Here, we are going to deploy a Redis and RedisSentinel instance using a supported version by KubeDB operator. Then we are going to create another RedisSentinel, and it will replace the old sentinel.
Prepare RedisSentinel
Now, we are going to deploy a RedisSentinel version 6.2.14.
apiVersion: kubedb.com/v1alpha2
kind: RedisSentinel
metadata:
name: sen-demo
namespace: demo
spec:
version: 6.2.14
replicas: 3
storageType: Durable
storage:
resources:
requests:
storage: 1Gi
storageClassName: "standard"
accessModes:
- ReadWriteOnce
terminationPolicy: WipeOut
Let’s create the RedisSentinel CR we have shown above,
$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.12.28/docs/examples/redis/sentinel/sentinel.yaml
redissentinel.kubedb.com/sen-demo created
Now, wait until sen-dmo has status Ready. i.e. ,
$ kubectl get redissentinel -n demo
NAME VERSION STATUS AGE
sen-demo 6.2.14 Ready 96s
Deploy Redis in Sentinel Mode
In this section, we are going to deploy a Redis database in Sentinel Mode.
apiVersion: kubedb.com/v1alpha2
kind: Redis
metadata:
name: rd-demo
namespace: demo
spec:
version: 6.2.14
replicas: 3
sentinelRef:
name: sen-demo
namespace: demo
mode: Sentinel
storageType: Durable
storage:
resources:
requests:
storage: 1Gi
storageClassName: "standard"
accessModes:
- ReadWriteOnce
terminationPolicy: WipeOut
Let’s create the Redis CR we have shown above,
$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.12.28/docs/examples/redis/sentinel/redis.yaml
redis.kubedb.com/rd-demo created
Now, wait until rd-demo has status Ready. i.e. ,
NAME VERSION STATUS AGE
rd-demo 6.2.14 Ready 67s
Lets exec into a sentinel pod, and make sure sentinel monitors redis master
$ kubectl exec -it -n demo sen-demo-0 -c redissentinel -- bash
root@sen-demo-0:/data# redis-cli -p 26379 sentinel masters
1) 1) "name"
2) "demo/rd-demo"
3) "ip"
4) "rd-demo-0.rd-demo-pods.demo.svc"
5) "port"
6) "6379"
7) "runid"
8) "ae368ff430018c9ef2e4c418aa1d5af1869e01a6"
9) "flags"
10) "master"
11) "link-pending-commands"
12) "0"
13) "link-refcount"
14) "1"
15) "last-ping-sent"
16) "0"
17) "last-ok-ping-reply"
18) "144"
19) "last-ping-reply"
20) "145"
21) "down-after-milliseconds"
22) "5000"
23) "info-refresh"
24) "755"
25) "role-reported"
26) "master"
27) "role-reported-time"
28) "103241"
29) "config-epoch"
30) "0"
31) "num-slaves"
32) "2"
33) "num-other-sentinels"
34) "2"
35) "quorum"
36) "2"
37) "failover-timeout"
38) "5000"
39) "parallel-syncs"
40) "1"
root@sen-demo-0:/data# exit
exit
Replace Sentinel
We are going to create a new RedisSentinel object for replacing.
apiVersion: kubedb.com/v1alpha2
kind: RedisSentinel
metadata:
name: new-sentinel
namespace: demo
spec:
version: 6.2.14
replicas: 3
storageType: Durable
storage:
resources:
requests:
storage: 1Gi
storageClassName: "standard"
accessModes:
- ReadWriteOnce
terminationPolicy: WipeOut
Let’s create the RedisSentinel CR we have shown above,
$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.12.28/docs/examples/redis/sentinel/new-sentinel.yaml
redissentinel.kubedb.com/new-sentinel created
Now, wait until new-sentinel has status Ready. i.e. ,
$ kubectl get redissentinel -n demo
NAME VERSION STATUS AGE
new-sentinel 6.2.14 Ready 60s
sen-demo 6.2.14 Ready 11m
Here, we are going to replace sen-demo with new-sentinel
Create RedisOpsRequest
In order to replace sentinel, we have to create a RedisOpsRequest CR with our desired resources. Below is the YAML of the RedisOpsRequest CR that we are going to create,
apiVersion: ops.kubedb.com/v1alpha1
kind: RedisOpsRequest
metadata:
name: replace-sentinel
namespace: demo
spec:
type: ReplaceSentinel
databaseRef:
name: rd-demo
sentinel:
ref:
name: new-sentinel
namespace: demo
removeUnusedSentinel: true
Here,
spec.databaseRef.namespecifies that we are performing vertical scaling operation onredisdatabase.spec.typespecifies that we are performingReplaceSentinelon our database.spec.sentinel.refspecifies reference of new sentinel.spec.sentienl.removeUnusedSentinelspecifies whether KubeDB operator should remove orphan Sentinel instance after replacing
Let’s create the RedisOpsRequest CR we have shown above,
$ kubectl apply -f https://github.com/kubedb/docs/raw/v2023.12.28/docs/examples/redis/sentinel/replace-sentinel.yaml
redisopsrequest.ops.kubedb.com/replace-sentinel created
Verify Replacement
If everything goes well, KubeDB Enterprise operator will update the sentinel of Redis object.
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
replace-sentinel ReplaceSentinel Successful 2m34s
We can see from the above output that the RedisOpsRequest has succeeded.
Now, we are going to verify from the Pod whether the sentinel of the database has updated, Let’s check. Lets exec into one of the new-sentinel pod and verify if it is following the master. And we can additionally check if old sentinel still following the database if it exists.
$ kubectl exec -it -n demo new-sentinel-0 -c redissentinel -- bash
root@new-sentinel-0:/data# redis-cli -p 26379 sentinel masters
1) 1) "name"
2) "demo/rd-demo"
3) "ip"
4) "rd-demo-0.rd-demo-pods.demo.svc"
5) "port"
6) "6379"
7) "runid"
8) "8af7fc2d42da77f92745b30c9e6bf7d2c21e3d33"
9) "flags"
10) "master"
11) "link-pending-commands"
12) "0"
13) "link-refcount"
14) "1"
15) "last-ping-sent"
16) "0"
17) "last-ok-ping-reply"
18) "798"
19) "last-ping-reply"
20) "798"
21) "down-after-milliseconds"
22) "5000"
23) "info-refresh"
24) "1350"
25) "role-reported"
26) "master"
27) "role-reported-time"
28) "240103"
29) "config-epoch"
30) "0"
31) "num-slaves"
32) "2"
33) "num-other-sentinels"
34) "2"
35) "quorum"
36) "2"
37) "failover-timeout"
38) "5000"
39) "parallel-syncs"
40) "1"
root@new-sentinel-0:/data# exit
exit
The above output verifies that we have successfully replaced sentinel of Redis database.
Cleaning up
First set termination policy to WipeOut all the things created by KubeDB operator for this Redis instance is deleted. Then delete the redis instance
to clean what you created in this tutorial.
$ kubectl patch -n demo rd/rd-demo -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
redis.kubedb.com/rd-demo patched
$ kubectl delete rd rd-demo -n demo
redis.kubedb.com "rd-demo" deleted
$ kubectl delete -n demo redisopsrequest replace-sentinel
redisopsrequest.ops.kubedb.com "replace-sentinel" deleted
Now delete the RedisSentinel instance similarly.
$ kubectl patch -n demo redissentinel/sen-demo -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
redissentinel.kubedb.com/sen-demo patched
$ kubectl delete redissentinel sen-demo -n demo
redis.kubedb.com "sen-demo" deleted
$ kubectl patch -n demo redissentinel/new-sentinel -p '{"spec":{"terminationPolicy":"WipeOut"}}' --type="merge"
redissentinel.kubedb.com/new-sentinel patched
$ kubectl delete redissentinel new-sentinel -n demo
redis.kubedb.com "new-sentinel" deleted
Next Steps
- Detail concepts of Redis object.
- Detail concepts of RedisSentinel object.
- Detail concepts of RedisVersion object.