New to KubeDB? Please start here.

Horizontal Scale MongoDB Replicaset

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

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/mongodb directory of kubedb/docs repository.

Apply Horizontal Scaling on Replicaset

Here, we are going to deploy a MongoDB replicaset using a supported version by KubeDB operator. Then we are going to apply horizontal scaling on it.

Prepare MongoDB Replicaset Database

Now, we are going to deploy a MongoDB replicaset database with version 4.2.3.

Deploy MongoDB replicaset

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

apiVersion: kubedb.com/v1alpha2
kind: MongoDB
metadata:
  name: mg-replicaset
  namespace: demo
spec:
  version: "4.2.3"
  replicaSet: 
    name: "replicaset"
  replicas: 3
  storageType: Durable
  storage:
    storageClassName: "standard"
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2021.11.24/docs/examples/mongodb/scaling/mg-replicaset.yaml
mongodb.kubedb.com/mg-replicaset created

Now, wait until mg-replicaset has status Ready. i.e,

$ kubectl get mg -n demo
NAME            VERSION   STATUS    AGE
mg-replicaset   4.2.3     Ready     2m36s

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

$ kubectl get mongodb -n demo mg-replicaset -o json | jq '.spec.replicas'
3

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

We can see from both command that the database has 3 replicas in the replicaset.

Also, we can verify the replicas of the replicaset from an internal mongodb command by execing into a replica.

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

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

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

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

$ kubectl exec -n demo  mg-replicaset-0  -- mongo admin -u root -p nrKuxni0wDSMrgwy --eval "db.adminCommand( { replSetGetStatus : 1 } ).members" --quiet
[
	{
		"_id" : 0,
		"name" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 1,
		"stateStr" : "PRIMARY",
		"uptime" : 171,
		"optime" : {
			"ts" : Timestamp(1614698544, 1),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:22:24Z"),
		"syncingTo" : "",
		"syncSourceHost" : "",
		"syncSourceId" : -1,
		"infoMessage" : "",
		"electionTime" : Timestamp(1614698393, 2),
		"electionDate" : ISODate("2021-03-02T15:19:53Z"),
		"configVersion" : 3,
		"self" : true,
		"lastHeartbeatMessage" : ""
	},
	{
		"_id" : 1,
		"name" : "mg-replicaset-1.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 2,
		"stateStr" : "SECONDARY",
		"uptime" : 128,
		"optime" : {
			"ts" : Timestamp(1614698544, 1),
			"t" : NumberLong(1)
		},
		"optimeDurable" : {
			"ts" : Timestamp(1614698544, 1),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:22:24Z"),
		"optimeDurableDate" : ISODate("2021-03-02T15:22:24Z"),
		"lastHeartbeat" : ISODate("2021-03-02T15:22:32.411Z"),
		"lastHeartbeatRecv" : ISODate("2021-03-02T15:22:31.543Z"),
		"pingMs" : NumberLong(0),
		"lastHeartbeatMessage" : "",
		"syncingTo" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceHost" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceId" : 0,
		"infoMessage" : "",
		"configVersion" : 3
	},
	{
		"_id" : 2,
		"name" : "mg-replicaset-2.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 2,
		"stateStr" : "SECONDARY",
		"uptime" : 83,
		"optime" : {
			"ts" : Timestamp(1614698544, 1),
			"t" : NumberLong(1)
		},
		"optimeDurable" : {
			"ts" : Timestamp(1614698544, 1),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:22:24Z"),
		"optimeDurableDate" : ISODate("2021-03-02T15:22:24Z"),
		"lastHeartbeat" : ISODate("2021-03-02T15:22:30.615Z"),
		"lastHeartbeatRecv" : ISODate("2021-03-02T15:22:31.543Z"),
		"pingMs" : NumberLong(0),
		"lastHeartbeatMessage" : "",
		"syncingTo" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceHost" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceId" : 0,
		"infoMessage" : "",
		"configVersion" : 3
	}
]

We can see from the above output that the replicaset has 3 nodes.

We are now ready to apply the MongoDBOpsRequest 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 MongoDBOpsRequest

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

apiVersion: ops.kubedb.com/v1alpha1
kind: MongoDBOpsRequest
metadata:
  name: mops-hscale-up-replicaset
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: mg-replicaset
  horizontalScaling:
    replicas: 4

Here,

  • spec.databaseRef.name specifies that we are performing horizontal scaling operation on mops-hscale-up-replicaset 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 MongoDBOpsRequest CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2021.11.24/docs/examples/mongodb/scaling/horizontal-scaling/mops-hscale-up-replicaset.yaml
mongodbopsrequest.ops.kubedb.com/mops-hscale-up-replicaset created

Verify Replicaset replicas scaled up successfully

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

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

$ watch kubectl get mongodbopsrequest -n demo
Every 2.0s: kubectl get mongodbopsrequest -n demo
NAME                        TYPE                STATUS       AGE
mops-hscale-up-replicaset   HorizontalScaling   Successful   106s

We can see from the above output that the MongoDBOpsRequest has succeeded. If we describe the MongoDBOpsRequest we will get an overview of the steps that were followed to scale the database.

$ kubectl describe mongodbopsrequest -n demo mops-hscale-up-replicaset                     
Name:         mops-hscale-up-replicaset
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         MongoDBOpsRequest
Metadata:
  Creation Timestamp:  2021-03-02T15:23:14Z
  Generation:          1
  Managed Fields:
    API Version:  ops.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:horizontalScaling:
          .:
          f:replicas:
        f:type:
    Manager:      kubectl-client-side-apply
    Operation:    Update
    Time:         2021-03-02T15:23:14Z
    API Version:  ops.kubedb.com/v1alpha1
    Fields Type:  FieldsV1
    fieldsV1:
      f:status:
        .:
        f:conditions:
        f:observedGeneration:
        f:phase:
    Manager:         kubedb-enterprise
    Operation:       Update
    Time:            2021-03-02T15:23:14Z
  Resource Version:  129882
  Self Link:         /apis/ops.kubedb.com/v1alpha1/namespaces/demo/mongodbopsrequests/mops-hscale-up-replicaset
  UID:               e97dac5c-5e3a-4153-9b31-8ba02af54bcb
Spec:
  Database Ref:
    Name:  mg-replicaset
  Horizontal Scaling:
    Replicas:  4
  Type:        HorizontalScaling
Status:
  Conditions:
    Last Transition Time:  2021-03-02T15:23:14Z
    Message:               MongoDB ops request is horizontally scaling database
    Observed Generation:   1
    Reason:                HorizontalScaling
    Status:                True
    Type:                  HorizontalScaling
    Last Transition Time:  2021-03-02T15:24:00Z
    Message:               Successfully Horizontally Scaled Up ReplicaSet
    Observed Generation:   1
    Reason:                ScaleUpReplicaSet
    Status:                True
    Type:                  ScaleUpReplicaSet
    Last Transition Time:  2021-03-02T15:24:00Z
    Message:               Successfully Horizontally Scaled MongoDB
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type    Reason             Age   From                        Message
  ----    ------             ----  ----                        -------
  Normal  PauseDatabase      91s   KubeDB Enterprise Operator  Pausing MongoDB demo/mg-replicaset
  Normal  PauseDatabase      91s   KubeDB Enterprise Operator  Successfully paused MongoDB demo/mg-replicaset
  Normal  ScaleUpReplicaSet  45s   KubeDB Enterprise Operator  Successfully Horizontally Scaled Up ReplicaSet
  Normal  ResumeDatabase     45s   KubeDB Enterprise Operator  Resuming MongoDB demo/mg-replicaset
  Normal  ResumeDatabase     45s   KubeDB Enterprise Operator  Successfully resumed MongoDB demo/mg-replicaset
  Normal  Successful         45s   KubeDB Enterprise Operator  Successfully Horizontally Scaled Database

Now, we are going to verify the number of replicas this database has from the MongoDB object, number of pods the statefulset have,

$ kubectl get mongodb -n demo mg-replicaset -o json | jq '.spec.replicas'
4

$ kubectl get sts -n demo mg-replicaset -o json | jq '.spec.replicas'
4

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

$ kubectl exec -n demo  mg-replicaset-0  -- mongo admin -u root -p nrKuxni0wDSMrgwy --eval "db.adminCommand( { replSetGetStatus : 1 } ).members" --quiet
[
	{
		"_id" : 0,
		"name" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 1,
		"stateStr" : "PRIMARY",
		"uptime" : 344,
		"optime" : {
			"ts" : Timestamp(1614698724, 1),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:25:24Z"),
		"syncingTo" : "",
		"syncSourceHost" : "",
		"syncSourceId" : -1,
		"infoMessage" : "",
		"electionTime" : Timestamp(1614698393, 2),
		"electionDate" : ISODate("2021-03-02T15:19:53Z"),
		"configVersion" : 4,
		"self" : true,
		"lastHeartbeatMessage" : ""
	},
	{
		"_id" : 1,
		"name" : "mg-replicaset-1.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 2,
		"stateStr" : "SECONDARY",
		"uptime" : 301,
		"optime" : {
			"ts" : Timestamp(1614698712, 2),
			"t" : NumberLong(1)
		},
		"optimeDurable" : {
			"ts" : Timestamp(1614698712, 2),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:25:12Z"),
		"optimeDurableDate" : ISODate("2021-03-02T15:25:12Z"),
		"lastHeartbeat" : ISODate("2021-03-02T15:25:23.889Z"),
		"lastHeartbeatRecv" : ISODate("2021-03-02T15:25:25.179Z"),
		"pingMs" : NumberLong(0),
		"lastHeartbeatMessage" : "",
		"syncingTo" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceHost" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceId" : 0,
		"infoMessage" : "",
		"configVersion" : 4
	},
	{
		"_id" : 2,
		"name" : "mg-replicaset-2.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 2,
		"stateStr" : "SECONDARY",
		"uptime" : 256,
		"optime" : {
			"ts" : Timestamp(1614698712, 2),
			"t" : NumberLong(1)
		},
		"optimeDurable" : {
			"ts" : Timestamp(1614698712, 2),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:25:12Z"),
		"optimeDurableDate" : ISODate("2021-03-02T15:25:12Z"),
		"lastHeartbeat" : ISODate("2021-03-02T15:25:23.888Z"),
		"lastHeartbeatRecv" : ISODate("2021-03-02T15:25:25.136Z"),
		"pingMs" : NumberLong(0),
		"lastHeartbeatMessage" : "",
		"syncingTo" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceHost" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceId" : 0,
		"infoMessage" : "",
		"configVersion" : 4
	},
	{
		"_id" : 3,
		"name" : "mg-replicaset-3.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 2,
		"stateStr" : "SECONDARY",
		"uptime" : 93,
		"optime" : {
			"ts" : Timestamp(1614698712, 2),
			"t" : NumberLong(1)
		},
		"optimeDurable" : {
			"ts" : Timestamp(1614698712, 2),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:25:12Z"),
		"optimeDurableDate" : ISODate("2021-03-02T15:25:12Z"),
		"lastHeartbeat" : ISODate("2021-03-02T15:25:23.926Z"),
		"lastHeartbeatRecv" : ISODate("2021-03-02T15:25:24.089Z"),
		"pingMs" : NumberLong(0),
		"lastHeartbeatMessage" : "",
		"syncingTo" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceHost" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceId" : 0,
		"infoMessage" : "",
		"configVersion" : 4
	}
]

From all the above outputs we can see that the replicas of the replicaset is 4. That means we have successfully scaled up the replicas of the MongoDB replicaset.

Scale Down Replicas

Here, we are going to scale down the replicas of the replicaset to meet the desired number of replicas after scaling.

Create MongoDBOpsRequest

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

apiVersion: ops.kubedb.com/v1alpha1
kind: MongoDBOpsRequest
metadata:
  name: mops-hscale-down-replicaset
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: mg-replicaset
  horizontalScaling:
    replicas: 3

Here,

  • spec.databaseRef.name specifies that we are performing horizontal scaling down operation on mops-hscale-down-replicaset 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 MongoDBOpsRequest CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2021.11.24/docs/examples/mongodb/scaling/horizontal-scaling/mops-hscale-down-replicaset.yaml
mongodbopsrequest.ops.kubedb.com/mops-hscale-down-replicaset created

Verify Replicaset replicas scaled down successfully

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

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

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

We can see from the above output that the MongoDBOpsRequest has succeeded. If we describe the MongoDBOpsRequest we will get an overview of the steps that were followed to scale the database.

$ kubectl describe mongodbopsrequest -n demo mops-hscale-down-replicaset                     
Name:         mops-hscale-down-replicaset
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         MongoDBOpsRequest
Metadata:
  Creation Timestamp:  2021-03-02T15:25:57Z
  Generation:          1
  Managed Fields:
    API Version:  ops.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:horizontalScaling:
          .:
          f:replicas:
        f:type:
    Manager:      kubectl-client-side-apply
    Operation:    Update
    Time:         2021-03-02T15:25:57Z
    API Version:  ops.kubedb.com/v1alpha1
    Fields Type:  FieldsV1
    fieldsV1:
      f:status:
        .:
        f:conditions:
        f:observedGeneration:
        f:phase:
    Manager:         kubedb-enterprise
    Operation:       Update
    Time:            2021-03-02T15:25:57Z
  Resource Version:  130393
  Self Link:         /apis/ops.kubedb.com/v1alpha1/namespaces/demo/mongodbopsrequests/mops-hscale-down-replicaset
  UID:               fbfee7f8-1dd5-4f58-aad7-ad2e2d66b295
Spec:
  Database Ref:
    Name:  mg-replicaset
  Horizontal Scaling:
    Replicas:  3
  Type:        HorizontalScaling
Status:
  Conditions:
    Last Transition Time:  2021-03-02T15:25:57Z
    Message:               MongoDB ops request is horizontally scaling database
    Observed Generation:   1
    Reason:                HorizontalScaling
    Status:                True
    Type:                  HorizontalScaling
    Last Transition Time:  2021-03-02T15:26:17Z
    Message:               Successfully Horizontally Scaled Down ReplicaSet
    Observed Generation:   1
    Reason:                ScaleDownReplicaSet
    Status:                True
    Type:                  ScaleDownReplicaSet
    Last Transition Time:  2021-03-02T15:26:17Z
    Message:               Successfully Horizontally Scaled MongoDB
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type    Reason               Age   From                        Message
  ----    ------               ----  ----                        -------
  Normal  PauseDatabase        50s   KubeDB Enterprise Operator  Pausing MongoDB demo/mg-replicaset
  Normal  PauseDatabase        50s   KubeDB Enterprise Operator  Successfully paused MongoDB demo/mg-replicaset
  Normal  ScaleDownReplicaSet  30s   KubeDB Enterprise Operator  Successfully Horizontally Scaled Down ReplicaSet
  Normal  ResumeDatabase       30s   KubeDB Enterprise Operator  Resuming MongoDB demo/mg-replicaset
  Normal  ResumeDatabase       30s   KubeDB Enterprise Operator  Successfully resumed MongoDB demo/mg-replicaset
  Normal  Successful           30s   KubeDB Enterprise Operator  Successfully Horizontally Scaled Database

Now, we are going to verify the number of replicas this database has from the MongoDB object, number of pods the statefulset have,

$ kubectl get mongodb -n demo mg-replicaset -o json | jq '.spec.replicas' 
3

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

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

$ kubectl exec -n demo  mg-replicaset-0  -- mongo admin -u root -p nrKuxni0wDSMrgwy --eval "db.adminCommand( { replSetGetStatus : 1 } ).members" --quiet 
[
	{
		"_id" : 0,
		"name" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 1,
		"stateStr" : "PRIMARY",
		"uptime" : 410,
		"optime" : {
			"ts" : Timestamp(1614698784, 1),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:26:24Z"),
		"syncingTo" : "",
		"syncSourceHost" : "",
		"syncSourceId" : -1,
		"infoMessage" : "",
		"electionTime" : Timestamp(1614698393, 2),
		"electionDate" : ISODate("2021-03-02T15:19:53Z"),
		"configVersion" : 5,
		"self" : true,
		"lastHeartbeatMessage" : ""
	},
	{
		"_id" : 1,
		"name" : "mg-replicaset-1.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 2,
		"stateStr" : "SECONDARY",
		"uptime" : 367,
		"optime" : {
			"ts" : Timestamp(1614698784, 1),
			"t" : NumberLong(1)
		},
		"optimeDurable" : {
			"ts" : Timestamp(1614698784, 1),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:26:24Z"),
		"optimeDurableDate" : ISODate("2021-03-02T15:26:24Z"),
		"lastHeartbeat" : ISODate("2021-03-02T15:26:29.423Z"),
		"lastHeartbeatRecv" : ISODate("2021-03-02T15:26:29.330Z"),
		"pingMs" : NumberLong(0),
		"lastHeartbeatMessage" : "",
		"syncingTo" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceHost" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceId" : 0,
		"infoMessage" : "",
		"configVersion" : 5
	},
	{
		"_id" : 2,
		"name" : "mg-replicaset-2.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"health" : 1,
		"state" : 2,
		"stateStr" : "SECONDARY",
		"uptime" : 322,
		"optime" : {
			"ts" : Timestamp(1614698784, 1),
			"t" : NumberLong(1)
		},
		"optimeDurable" : {
			"ts" : Timestamp(1614698784, 1),
			"t" : NumberLong(1)
		},
		"optimeDate" : ISODate("2021-03-02T15:26:24Z"),
		"optimeDurableDate" : ISODate("2021-03-02T15:26:24Z"),
		"lastHeartbeat" : ISODate("2021-03-02T15:26:31.022Z"),
		"lastHeartbeatRecv" : ISODate("2021-03-02T15:26:31.224Z"),
		"pingMs" : NumberLong(0),
		"lastHeartbeatMessage" : "",
		"syncingTo" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceHost" : "mg-replicaset-0.mg-replicaset-pods.demo.svc.cluster.local:27017",
		"syncSourceId" : 0,
		"infoMessage" : "",
		"configVersion" : 5
	}
]

From all the above outputs we can see that the replicas of the replicaset is 3. That means we have successfully scaled down the replicas of the MongoDB replicaset.

Cleaning Up

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

kubectl delete mg -n demo mg-replicaset
kubectl delete mongodbopsrequest -n demo mops-vscale-replicaset