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Autoscaling the Compute Resource of a MongoDB Replicaset Database

This guide will show you how to use KubeDB to autoscale compute resources i.e. cpu and memory of a MongoDB replicaset database.

Before You Begin

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.

Autoscaling of Replicaset Database

Here, we are going to deploy a MongoDB Replicaset using a supported version by KubeDB operator. Then we are going to apply MongoDBAutoscaler to set up autoscaling.

Deploy MongoDB Replicaset

In this section, we are going to deploy a MongoDB Replicaset database with version 4.2.3. Then, in the next section we will set up autoscaling for this database using MongoDBAutoscaler CRD. Below is the YAML of the MongoDB CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: MongoDB
metadata:
  name: mg-rs
  namespace: demo
spec:
  version: "4.2.3"
  storageType: Durable
  storage:
    resources:
      requests:
        storage: 1Gi
  podTemplate:
    spec:
      resources:
        requests:
          cpu: "200m"
          memory: "300Mi"
        limits:
          cpu: "200m"
          memory: "300Mi"
  terminationPolicy: WipeOut

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2021.04.16/docs/examples/mongodb/autoscaling/compute/mg-rs.yaml
mongodb.kubedb.com/mg-rs created

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

$ kubectl get mg -n demo
NAME    VERSION    STATUS    AGE
mg-rs   4.2.3      Ready     2m53s

Let’s check the Pod containers resources,

$ kubectl get pod -n demo mg-rs-0 -o json | jq '.spec.containers[].resources'
{
  "limits": {
    "cpu": "200m",
    "memory": "300Mi"
  },
  "requests": {
    "cpu": "200m",
    "memory": "300Mi"
  }
}

Let’s check the MongoDB resources,

$ kubectl get mongodb -n demo mg-rs -o json | jq '.spec.podTemplate.spec.resources'
{
  "limits": {
    "cpu": "200m",
    "memory": "300Mi"
  },
  "requests": {
    "cpu": "200m",
    "memory": "300Mi"
  }
}

You can see from the above outputs that the resources are same as the one we have assigned while deploying the mongodb.

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

Compute Resource Autoscaling

Here, we are going to set up compute resource autoscaling using a MongoDBAutoscaler Object.

Create MongoDBAutoscaler Object

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

apiVersion: autoscaling.kubedb.com/v1alpha1
kind: MongoDBAutoscaler
metadata:
  name: mg-as-rs
  namespace: demo
spec:
  databaseRef:
    name: mg-rs
  compute:
    replicaSet:
      trigger: "On"
      podLifeTimeThreshold: 5m
      minAllowed:
        cpu: 250m
        memory: 350Mi
      maxAllowed:
        cpu: 1
        memory: 1Gi
      controlledResources: ["cpu", "memory"]

Here,

  • spec.databaseRef.name specifies that we are performing compute resource scaling operation on mg-rs database.
  • spec.compute.replicaSet.trigger specifies that compute autoscaling is enabled for this database.
  • spec.compute.replicaSet.podLifeTimeThreshold specifies the minimum lifetime for at least one of the pod to initiate a vertical scaling.
  • spec.compute.replicaSet.minAllowed specifies the minimum allowed resources for the database.
  • spec.compute.replicaSet.maxAllowed specifies the maximum allowed resources for the database.
  • spec.compute.replicaSet.controlledResources specifies the resources that are controlled by the autoscaler.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2021.04.16/docs/examples/mongodb/autoscaling/compute/mg-as-rs.yaml
mongodbautoscaler.autoscaling.kubedb.com/mg-as-rs created

Verify Autoscaling is set up successfully

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

$ kubectl get mongodbautoscaler -n demo
NAME        AGE
mg-as-rs    102s

$ kubectl describe mongodbautoscaler mg-as-rs -n demo
Name:         mg-as-rs
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  autoscaling.kubedb.com/v1alpha1
Kind:         MongoDBAutoscaler
Metadata:
  Creation Timestamp:  2021-03-06T19:10:46Z
  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:compute:
          .:
          f:replicaSet:
            .:
            f:controlledResources:
            f:maxAllowed:
              .:
              f:cpu:
              f:memory:
            f:minAllowed:
              .:
              f:cpu:
              f:memory:
            f:podLifeTimeThreshold:
            f:trigger:
        f:databaseRef:
          .:
          f:name:
    Manager:         kubectl-client-side-apply
    Operation:       Update
    Time:            2021-03-06T19:10:46Z
  Resource Version:  839193
  Self Link:         /apis/autoscaling.kubedb.com/v1alpha1/namespaces/demo/mongodbautoscalers/mg-as-rs
  UID:               9be99253-7475-43fe-a68a-34eaec3225c6
Spec:
  Compute:
    Replica Set:
      Controlled Resources:
        cpu
        memory
      Max Allowed:
        Cpu:     1
        Memory:  1Gi
      Min Allowed:
        Cpu:                    250m
        Memory:                 350Mi
      Pod Life Time Threshold:  5m0s
      Trigger:                  On
  Database Ref:
    Name:  mg-rs
Events:    <none>

So, the mongodbautoscaler resource is created successfully.

Now, lets verify that the vertical pod autoscaler (vpa) resource is created successfully,

$ kubectl get vpa -n demo
NAME        AGE
vpa-mg-rs   7s

$ kubectl describe vpa vpa-mg-rs -n demo
Name:         vpa-mg-rs
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  autoscaling.k8s.io/v1
Kind:         VerticalPodAutoscaler
Metadata:
  Creation Timestamp:  2021-03-06T19:10:46Z
  Generation:          2
  Managed Fields:
    API Version:  autoscaling.k8s.io/v1
    Fields Type:  FieldsV1
    fieldsV1:
      f:metadata:
        f:ownerReferences:
          .:
          k:{"uid":"9be99253-7475-43fe-a68a-34eaec3225c6"}:
            .:
            f:apiVersion:
            f:blockOwnerDeletion:
            f:controller:
            f:kind:
            f:name:
            f:uid:
      f:spec:
        .:
        f:resourcePolicy:
          .:
          f:containerPolicies:
        f:targetRef:
          .:
          f:apiVersion:
          f:kind:
          f:name:
        f:updatePolicy:
          .:
          f:updateMode:
      f:status:
    Manager:      kubedb-autoscaler
    Operation:    Update
    Time:         2021-03-06T19:10:46Z
    API Version:  autoscaling.k8s.io/v1
    Fields Type:  FieldsV1
    fieldsV1:
      f:status:
        f:conditions:
        f:recommendation:
          .:
          f:containerRecommendations:
    Manager:    recommender
    Operation:  Update
    Time:       2021-03-06T19:10:59Z
  Owner References:
    API Version:           autoscaling.kubedb.com/v1alpha1
    Block Owner Deletion:  true
    Controller:            true
    Kind:                  MongoDBAutoscaler
    Name:                  mg-as-rs
    UID:                   9be99253-7475-43fe-a68a-34eaec3225c6
  Resource Version:        839239
  Self Link:               /apis/autoscaling.k8s.io/v1/namespaces/demo/verticalpodautoscalers/vpa-mg-rs
  UID:                     fd2d9896-2eee-43df-85a6-1b968f8d2862
Spec:
  Resource Policy:
    Container Policies:
      Container Name:  mongodb
      Controlled Resources:
        cpu
        memory
      Controlled Values:  RequestsAndLimits
      Max Allowed:
        Cpu:     1
        Memory:  1Gi
      Min Allowed:
        Cpu:           250m
        Memory:        350Mi
      Container Name:  replication-mode-detector
      Mode:            Off
  Target Ref:
    API Version:  apps/v1
    Kind:         StatefulSet
    Name:         mg-rs
  Update Policy:
    Update Mode:  Off
Status:
  Conditions:
    Last Transition Time:  2021-03-06T07:21:58Z
    Status:                False
    Type:                  RecommendationProvided
  Recommendation:
Events:  <none>

So, we can verify from the above output that the vpa resource is created successfully. But you can see that the RecommendationProvided is false and also the Recommendation section of the vpa is empty. Let’s wait some time and describe the vpa again.

$ kubectl describe vpa vpa-mg-rs -n demo
Name:         vpa-mg-rs
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  autoscaling.k8s.io/v1
Kind:         VerticalPodAutoscaler
Metadata:
  Creation Timestamp:  2021-03-06T19:10:46Z
  Generation:          2
  Managed Fields:
    API Version:  autoscaling.k8s.io/v1
    Fields Type:  FieldsV1
    fieldsV1:
      f:metadata:
        f:ownerReferences:
          .:
          k:{"uid":"9be99253-7475-43fe-a68a-34eaec3225c6"}:
            .:
            f:apiVersion:
            f:blockOwnerDeletion:
            f:controller:
            f:kind:
            f:name:
            f:uid:
      f:spec:
        .:
        f:resourcePolicy:
          .:
          f:containerPolicies:
        f:targetRef:
          .:
          f:apiVersion:
          f:kind:
          f:name:
        f:updatePolicy:
          .:
          f:updateMode:
      f:status:
    Manager:      kubedb-autoscaler
    Operation:    Update
    Time:         2021-03-06T19:10:46Z
    API Version:  autoscaling.k8s.io/v1
    Fields Type:  FieldsV1
    fieldsV1:
      f:status:
        f:conditions:
        f:recommendation:
          .:
          f:containerRecommendations:
    Manager:    recommender
    Operation:  Update
    Time:       2021-03-06T19:10:59Z
  Owner References:
    API Version:           autoscaling.kubedb.com/v1alpha1
    Block Owner Deletion:  true
    Controller:            true
    Kind:                  MongoDBAutoscaler
    Name:                  mg-as-rs
    UID:                   9be99253-7475-43fe-a68a-34eaec3225c6
  Resource Version:        839239
  Self Link:               /apis/autoscaling.k8s.io/v1/namespaces/demo/verticalpodautoscalers/vpa-mg-rs
  UID:                     fd2d9896-2eee-43df-85a6-1b968f8d2862
Spec:
  Resource Policy:
    Container Policies:
      Container Name:  mongodb
      Controlled Resources:
        cpu
        memory
      Controlled Values:  RequestsAndLimits
      Max Allowed:
        Cpu:     1
        Memory:  1Gi
      Min Allowed:
        Cpu:           250m
        Memory:        350Mi
      Container Name:  replication-mode-detector
      Mode:            Off
  Target Ref:
    API Version:  apps/v1
    Kind:         StatefulSet
    Name:         mg-rs
  Update Policy:
    Update Mode:  Off
Status:
  Conditions:
    Last Transition Time:  2021-03-06T19:10:59Z
    Status:                True
    Type:                  RecommendationProvided
  Recommendation:
    Container Recommendations:
      Container Name:  mongodb
      Lower Bound:
        Cpu:     250m
        Memory:  350Mi
      Target:
        Cpu:     250m
        Memory:  350Mi
      Uncapped Target:
        Cpu:     182m
        Memory:  262144k
      Upper Bound:
        Cpu:     1
        Memory:  1Gi
Events:          <none>

As you can see from the output the vpa has generated a recommendation for our database. Our autoscaler operator continuously watches the recommendation generated and creates an mongodbopsrequest based on the recommendations, if the database pods are needed to scaled up or down.

Let’s watch the mongodbopsrequest in the demo namespace to see if any mongodbopsrequest object is created. After some time you’ll see that a mongodbopsrequest will be created based on the recommendation.

$ watch kubectl get mongodbopsrequest -n demo
Every 2.0s: kubectl get mongodbopsrequest -n demo
NAME                    TYPE              STATUS       AGE
mops-vpa-mg-rs-l3ulmr   VerticalScaling   Progressing  10s

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

$ watch kubectl get mongodbopsrequest -n demo
Every 2.0s: kubectl get mongodbopsrequest -n demo
NAME                    TYPE              STATUS       AGE
mops-vpa-mg-rs-l3ulmr   VerticalScaling   Successful   68s

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-vpa-mg-rs-l3ulmr
Name:         mops-vpa-mg-rs-l3ulmr
Namespace:    demo
Labels:       app.kubernetes.io/component=database
              app.kubernetes.io/instance=mg-rs
              app.kubernetes.io/managed-by=kubedb.com
              app.kubernetes.io/name=mongodbs.kubedb.com
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         MongoDBOpsRequest
Metadata:
  Creation Timestamp:  2021-03-07T15:55:12Z
  Generation:          1
  Managed Fields:
    API Version:  ops.kubedb.com/v1alpha1
    Fields Type:  FieldsV1
    fieldsV1:
      f:metadata:
        f:labels:
          .:
          f:app.kubernetes.io/component:
          f:app.kubernetes.io/instance:
          f:app.kubernetes.io/managed-by:
          f:app.kubernetes.io/name:
        f:ownerReferences:
      f:spec:
        .:
        f:configuration:
        f:databaseRef:
          .:
          f:name:
        f:type:
        f:verticalScaling:
          .:
          f:replicaSet:
            .:
            f:limits:
              .:
              f:cpu:
              f:memory:
            f:requests:
              .:
              f:cpu:
              f:memory:
    Manager:      kubedb-autoscaler
    Operation:    Update
    Time:         2021-03-07T15:55:12Z
    API Version:  ops.kubedb.com/v1alpha1
    Fields Type:  FieldsV1
    fieldsV1:
      f:status:
        .:
        f:conditions:
        f:observedGeneration:
        f:phase:
    Manager:    kubedb-enterprise
    Operation:  Update
    Time:       2021-03-07T15:55:12Z
  Owner References:
    API Version:           autoscaling.kubedb.com/v1alpha1
    Block Owner Deletion:  true
    Controller:            true
    Kind:                  MongoDBAutoscaler
    Name:                  mg-as-rs
    UID:                   9be99253-7475-43fe-a68a-34eaec3225c6
  Resource Version:        868114
  Self Link:               /apis/ops.kubedb.com/v1alpha1/namespaces/demo/mongodbopsrequests/mops-vpa-mg-rs-l3ulmr
  UID:                     2029223c-25d3-4ecb-b71f-ff0f93a2e4b6
Spec:
  Configuration:
  Database Ref:
    Name:  mg-rs
  Type:    VerticalScaling
  Vertical Scaling:
    Replica Set:
      Limits:
        Cpu:     250m
        Memory:  350Mi
      Requests:
        Cpu:     250m
        Memory:  350Mi
Status:
  Conditions:
    Last Transition Time:  2021-03-07T15:55:12Z
    Message:               MongoDB ops request is vertically scaling database
    Observed Generation:   1
    Reason:                VerticalScaling
    Status:                True
    Type:                  VerticalScaling
    Last Transition Time:  2021-03-07T15:55:12Z
    Message:               Successfully updated StatefulSets Resources
    Observed Generation:   1
    Reason:                UpdateStatefulSetResources
    Status:                True
    Type:                  UpdateStatefulSetResources
    Last Transition Time:  2021-03-07T15:57:22Z
    Message:               Successfully Vertically Scaled Replicaset Resources
    Observed Generation:   1
    Reason:                UpdateReplicaSetResources
    Status:                True
    Type:                  UpdateReplicaSetResources
    Last Transition Time:  2021-03-07T15:57:22Z
    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  Starting                    2m21s  KubeDB Enterprise Operator  Updating Resources of StatefulSet: mg-rs
  Normal  UpdateStatefulSetResources  2m21s  KubeDB Enterprise Operator  Successfully updated StatefulSets Resources
  Normal  UpdateReplicaSetResources   11s    KubeDB Enterprise Operator  Successfully Vertically Scaled Replicaset Resources
  Normal  ResumeDatabase              11s    KubeDB Enterprise Operator  Resuming MongoDB demo/mg-rs
  Normal  ResumeDatabase              11s    KubeDB Enterprise Operator  Successfully resumed MongoDB demo/mg-rs
  Normal  Successful                  11s    KubeDB Enterprise Operator  Successfully Vertically Scaled Database

Now, we are going to verify from the Pod, and the MongoDB 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-rs-0 -o json | jq '.spec.containers[].resources'
{
  "limits": {
    "cpu": "250m",
    "memory": "350Mi"
  },
  "requests": {
    "cpu": "250m",
    "memory": "350Mi"
  }
}

$ kubectl get mongodb -n demo mg-rs -o json | jq '.spec.podTemplate.spec.resources'
{
  "limits": {
    "cpu": "250m",
    "memory": "350Mi"
  },
  "requests": {
    "cpu": "250m",
    "memory": "350Mi"
  }
}

The above output verifies that we have successfully auto scaled 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-rs
kubectl delete mongodbautoscaler -n demo mg-as-rs