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Vertical Scale MongoDB Replicaset

This guide will show you how to use KubeDB Ops-manager operator to update the resources of a MongoDB replicaset 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 Provisioner and Ops-manager 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 Vertical 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 vertical scaling on it.

Prepare MongoDB Replicaset Database

Now, we are going to deploy a MongoDB replicaset database with version 4.4.26.

Deploy MongoDB replicaset

In this section, we are going to deploy a MongoDB replicaset database. Then, in the next section we will update the resources of 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: "4.4.26"
  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/v2024.4.27/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   4.4.26      Ready     3m46s

Let’s check the Pod containers resources,

$ kubectl get pod -n demo mg-replicaset-0 -o json | jq '.spec.containers[].resources'
{
  "limits": {
    "cpu": "500m",
    "memory": "1Gi"
  },
  "requests": {
    "cpu": "500m",
    "memory": "1Gi"
  }
}

You can see the Pod has the default resources which is assigned by Kubedb operator.

We are now ready to apply the MongoDBOpsRequest CR to update the resources of this database.

Vertical Scaling

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

Create MongoDBOpsRequest

In order to update the resources of the database, we have to create a MongoDBOpsRequest CR with our desired resources. Below is the YAML of the MongoDBOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: MongoDBOpsRequest
metadata:
  name: mops-vscale-replicaset
  namespace: demo
spec:
  type: VerticalScaling
  databaseRef:
    name: mg-replicaset
  verticalScaling:
    replicaSet:
      resources:
        requests:
          memory: "1.2Gi"
          cpu: "0.6"
        limits:
          memory: "1.2Gi"
          cpu: "0.6"
  readinessCriteria:
    oplogMaxLagSeconds: 20
    objectsCountDiffPercentage: 10
  timeout: 5m
  apply: IfReady

Here,

spec.databaseRef.name specifies that we are performing vertical scaling operation on mops-vscale-replicaset database.
spec.type specifies that we are performing VerticalScaling on our database.
spec.VerticalScaling.replicaSet specifies the desired resources after scaling.
spec.VerticalScaling.arbiter could also be specified in similar fashion to get the desired resources for arbiter pod.
Have a look here on the respective sections to understand the readinessCriteria, timeout & apply fields.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2024.4.27/docs/examples/mongodb/scaling/vertical-scaling/mops-vscale-replicaset.yaml
mongodbopsrequest.ops.kubedb.com/mops-vscale-replicaset created

Verify MongoDB Replicaset resources updated successfully

If everything goes well, KubeDB Ops-manager operator will update the resources of MongoDB object and related StatefulSets and Pods.

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

$ kubectl get mongodbopsrequest -n demo
Every 2.0s: kubectl get mongodbopsrequest -n demo
NAME                     TYPE              STATUS       AGE
mops-vscale-replicaset   VerticalScaling   Successful   3m56s

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-vscale-replicaset
Name:         mops-vscale-replicaset
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         MongoDBOpsRequest
Metadata:
  Creation Timestamp:  2022-10-26T10:41:56Z
  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:apply:
        f:databaseRef:
        f:readinessCriteria:
          .:
          f:objectsCountDiffPercentage:
          f:oplogMaxLagSeconds:
        f:timeout:
        f:type:
        f:verticalScaling:
          .:
          f:replicaSet:
            .:
            f:limits:
              .:
              f:cpu:
              f:memory:
            f:requests:
              .:
              f:cpu:
              f:memory:
    Manager:      kubectl-client-side-apply
    Operation:    Update
    Time:         2022-10-26T10:41:56Z
    API Version:  ops.kubedb.com/v1alpha1
    Fields Type:  FieldsV1
    fieldsV1:
      f:status:
        .:
        f:conditions:
        f:observedGeneration:
        f:phase:
    Manager:         kubedb-ops-manager
    Operation:       Update
    Subresource:     status
    Time:            2022-10-26T10:44:33Z
  Resource Version:  611468
  UID:               474053a7-90a8-49fd-9b27-c9bf7b4660e7
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  mg-replicaset
  Readiness Criteria:
    Objects Count Diff Percentage:  10
    Oplog Max Lag Seconds:          20
  Timeout:                          5m
  Type:                             VerticalScaling
  Vertical Scaling:
    Replica Set:
      Limits:
        Cpu:     0.6
        Memory:  1.2Gi
      Requests:
        Cpu:     0.6
        Memory:  1.2Gi
Status:
  Conditions:
    Last Transition Time:  2022-10-26T10:43:21Z
    Message:               MongoDB ops request is vertically scaling database
    Observed Generation:   1
    Reason:                VerticalScaling
    Status:                True
    Type:                  VerticalScaling
    Last Transition Time:  2022-10-26T10:44:33Z
    Message:               Successfully Vertically Scaled Replicaset Resources
    Observed Generation:   1
    Reason:                UpdateReplicaSetResources
    Status:                True
    Type:                  UpdateReplicaSetResources
    Last Transition Time:  2022-10-26T10:44:33Z
    Message:               Successfully Vertically Scaled Database
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type    Reason                     Age   From                         Message
  ----    ------                     ----  ----                         -------
  Normal  PauseDatabase              82s   KubeDB Ops-manager Operator  Pausing MongoDB demo/mg-replicaset
  Normal  PauseDatabase              82s   KubeDB Ops-manager Operator  Successfully paused MongoDB demo/mg-replicaset
  Normal  Starting                   82s   KubeDB Ops-manager Operator  Updating Resources of StatefulSet: mg-replicaset
  Normal  UpdateReplicaSetResources  82s   KubeDB Ops-manager Operator  Successfully updated replicaset Resources
  Normal  Starting                   82s   KubeDB Ops-manager Operator  Updating Resources of StatefulSet: mg-replicaset
  Normal  UpdateReplicaSetResources  82s   KubeDB Ops-manager Operator  Successfully updated replicaset Resources
  Normal  UpdateReplicaSetResources  10s   KubeDB Ops-manager Operator  Successfully Vertically Scaled Replicaset Resources
  Normal  ResumeDatabase             10s   KubeDB Ops-manager Operator  Resuming MongoDB demo/mg-replicaset
  Normal  ResumeDatabase             10s   KubeDB Ops-manager Operator  Successfully resumed MongoDB demo/mg-replicaset
  Normal  Successful                 10s   KubeDB Ops-manager Operator  Successfully Vertically Scaled Database

Now, we are going to verify from one of the Pod yaml whether the resources of the replicaset database has updated to meet up the desired state, Let’s check,

$ kubectl get pod -n demo mg-replicaset-0 -o json | jq '.spec.containers[].resources'
{
  "limits": {
    "cpu": "600m",
    "memory": "1288490188800m"
  },
  "requests": {
    "cpu": "600m",
    "memory": "1288490188800m"
  }
}

The above output verifies that we have successfully scaled up the resources of the MongoDB replicaset database.

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

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