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New to KubeDB? Please start here.

Horizontal Scale FerretDB

This guide will show you how to use KubeDB Ops-manager operator to scale the replicaset of a FerretDB.

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/ferretdb directory of kubedb/docs repository.

Apply Horizontal Scaling on ferretdb

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

Prepare FerretDB

Now, we are going to deploy a FerretDB with version 1.23.0.

Deploy FerretDB

In this section, we are going to deploy a FerretDB. Then, in the next section we will scale the ferretdb using FerretDBOpsRequest CRD. Below is the YAML of the FerretDB CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: FerretDB
metadata:
  name: fr-horizontal
  namespace: demo
spec:
  version: "2.0.0"
  storage:
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: 500Mi
  deletionPolicy: WipeOut
  server:
    primary:
      replicas: 1

$ kubectl create -f https://github.com/kubedb/docs/raw/v2025.3.24/docs/examples/ferretdb/scaling/fr-horizontal.yaml
ferretdb.kubedb.com/fr-horizontal created

Now, wait until fr-horizontal has status Ready. i.e,

$ kubectl get fr -n demo
NAME            NAMESPACE   VERSION   STATUS   AGE
fr-horizontal   demo        2.0.0     Ready    86s

Let’s check the number of replicas this ferretdb has from the FerretDB object, number of pods the petset have,

$ kubectl get fr -n demo fr-horizontal -o json | jq '.spec.server.primary.replicas'
1

$ kubectl get petset -n demo fr-horizontal -o json | jq '.spec.replicas'
1

We can see from both command that the ferretdb primary server has 1 replicas.

We are now ready to apply the FerretDBOpsRequest CR to scale this ferretdb.

Scale Up Replicas

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

Create FerretDBOpsRequest

In order to scale up the replicas of the ferretdb primary server, we have to create a FerretDBOpsRequest CR with our desired replicas. Below is the YAML of the FerretDBOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: FerretDBOpsRequest
metadata:
  name: ferretdb-horizontal-scale-up
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: fr-horizontal
  horizontalScaling:
    primary:
      replicas: 3

Here,

  • spec.databaseRef.name specifies that we are performing horizontal scaling operation on fr-horizontal ferretdb.
  • spec.type specifies that we are performing HorizontalScaling on our ferretdb.
  • spec.horizontalScaling.primary.replicas specifies the desired primary server replicas after scaling.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2025.3.24/docs/examples/ferretdb/scaling/horizontal-scaling/frops-hscale-up-ops.yaml
ferretdbopsrequest.ops.kubedb.com/ferretdb-horizontal-scale-up created

Verify replicas scaled up successfully

If everything goes well, KubeDB Ops-manager operator will update the replicas of FerretDB object and related PetSet.

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

$ watch kubectl get ferretdbopsrequest -n demo
Every 2.0s: kubectl get ferretdbopsrequest -n demo
NAME                           TYPE                STATUS       AGE
ferretdb-horizontal-scale-up   HorizontalScaling   Successful   102s

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

$ kubectl describe ferretdbopsrequest -n demo ferretdb-horizontal-scale-up
Name:         ferretdb-horizontal-scale-up
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         FerretDBOpsRequest
Metadata:
  Creation Timestamp:  2025-04-08T06:23:50Z
  Generation:          1
  Resource Version:    64728
  UID:                 ba4b687c-7127-46a6-bf01-9c5d5d916555
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  fr-horizontal
  Horizontal Scaling:
    Primary:
      Replicas:  3
  Type:          HorizontalScaling
Status:
  Conditions:
    Last Transition Time:  2025-04-08T06:23:51Z
    Message:               FerretDB ops-request has started to horizontally scaling the nodes
    Observed Generation:   1
    Reason:                HorizontalScaling
    Status:                True
    Type:                  HorizontalScaling
    Last Transition Time:  2025-04-08T06:23:54Z
    Message:               Successfully paused database
    Observed Generation:   1
    Reason:                DatabasePauseSucceeded
    Status:                True
    Type:                  DatabasePauseSucceeded
    Last Transition Time:  2025-04-08T06:24:19Z
    Message:               Successfully Scaled Up Node
    Observed Generation:   1
    Reason:                HorizontalScaleUp
    Status:                True
    Type:                  HorizontalScaleUp
    Last Transition Time:  2025-04-08T06:23:59Z
    Message:               patch petset; ConditionStatus:True; PodName:fr-horizontal-1
    Observed Generation:   1
    Status:                True
    Type:                  PatchPetset--fr-horizontal-1
    Last Transition Time:  2025-04-08T06:24:04Z
    Message:               is pod ready; ConditionStatus:True; PodName:fr-horizontal-1
    Observed Generation:   1
    Status:                True
    Type:                  IsPodReady--fr-horizontal-1
    Last Transition Time:  2025-04-08T06:24:04Z
    Message:               client failure; ConditionStatus:True; PodName:fr-horizontal-1
    Observed Generation:   1
    Status:                True
    Type:                  ClientFailure--fr-horizontal-1
    Last Transition Time:  2025-04-08T06:24:04Z
    Message:               is node healthy; ConditionStatus:True; PodName:fr-horizontal-1
    Observed Generation:   1
    Status:                True
    Type:                  IsNodeHealthy--fr-horizontal-1
    Last Transition Time:  2025-04-08T06:24:09Z
    Message:               patch petset; ConditionStatus:True; PodName:fr-horizontal-2
    Observed Generation:   1
    Status:                True
    Type:                  PatchPetset--fr-horizontal-2
    Last Transition Time:  2025-04-08T06:24:09Z
    Message:               fr-horizontal already has desired replicas
    Observed Generation:   1
    Reason:                HorizontalScale
    Status:                True
    Type:                  HorizontalScale
    Last Transition Time:  2025-04-08T06:24:14Z
    Message:               is pod ready; ConditionStatus:True; PodName:fr-horizontal-2
    Observed Generation:   1
    Status:                True
    Type:                  IsPodReady--fr-horizontal-2
    Last Transition Time:  2025-04-08T06:24:14Z
    Message:               client failure; ConditionStatus:True; PodName:fr-horizontal-2
    Observed Generation:   1
    Status:                True
    Type:                  ClientFailure--fr-horizontal-2
    Last Transition Time:  2025-04-08T06:24:14Z
    Message:               is node healthy; ConditionStatus:True; PodName:fr-horizontal-2
    Observed Generation:   1
    Status:                True
    Type:                  IsNodeHealthy--fr-horizontal-2
    Last Transition Time:  2025-04-08T06:24:19Z
    Message:               Successfully updated FerretDB
    Observed Generation:   1
    Reason:                UpdateDatabase
    Status:                True
    Type:                  UpdateDatabase
    Last Transition Time:  2025-04-08T06:24:19Z
    Message:               Successfully completed the HorizontalScaling for FerretDB
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                                                          Age   From                         Message
  ----     ------                                                          ----  ----                         -------
  Normal   Starting                                                        43s   KubeDB Ops-manager Operator  Start processing for FerretDBOpsRequest: demo/ferretdb-horizontal-scale-up
  Normal   Starting                                                        43s   KubeDB Ops-manager Operator  Pausing FerretDB database: demo/fr-horizontal
  Normal   Successful                                                      43s   KubeDB Ops-manager Operator  Successfully paused FerretDB database: demo/fr-horizontal for FerretDBOpsRequest: ferretdb-horizontal-scale-up
  Warning  patch petset; ConditionStatus:True; PodName:fr-horizontal-1     35s   KubeDB Ops-manager Operator  patch petset; ConditionStatus:True; PodName:fr-horizontal-1
  Warning  is pod ready; ConditionStatus:True; PodName:fr-horizontal-1     30s   KubeDB Ops-manager Operator  is pod ready; ConditionStatus:True; PodName:fr-horizontal-1
  Warning  client failure; ConditionStatus:True; PodName:fr-horizontal-1   30s   KubeDB Ops-manager Operator  client failure; ConditionStatus:True; PodName:fr-horizontal-1
  Warning  is node healthy; ConditionStatus:True; PodName:fr-horizontal-1  30s   KubeDB Ops-manager Operator  is node healthy; ConditionStatus:True; PodName:fr-horizontal-1
  Warning  patch petset; ConditionStatus:True; PodName:fr-horizontal-2     25s   KubeDB Ops-manager Operator  patch petset; ConditionStatus:True; PodName:fr-horizontal-2
  Warning  is pod ready; ConditionStatus:True; PodName:fr-horizontal-2     20s   KubeDB Ops-manager Operator  is pod ready; ConditionStatus:True; PodName:fr-horizontal-2
  Warning  client failure; ConditionStatus:True; PodName:fr-horizontal-2   20s   KubeDB Ops-manager Operator  client failure; ConditionStatus:True; PodName:fr-horizontal-2
  Warning  is node healthy; ConditionStatus:True; PodName:fr-horizontal-2  20s   KubeDB Ops-manager Operator  is node healthy; ConditionStatus:True; PodName:fr-horizontal-2
  Normal   HorizontalScaleUp                                               15s   KubeDB Ops-manager Operator  Successfully Scaled Up Node
  Normal   UpdateDatabase                                                  15s   KubeDB Ops-manager Operator  Successfully updated FerretDB
  Normal   Starting                                                        15s   KubeDB Ops-manager Operator  Resuming FerretDB database: demo/fr-horizontal
  Normal   Successful                                                      15s   KubeDB Ops-manager Operator  Successfully resumed FerretDB database: demo/fr-horizontal for FerretDBOpsRequest: ferretdb-horizontal-scale-up

Now, we are going to verify the number of replicas this ferretdb has from the FerretDB object, number of pods the petset have,

$ kubectl get fr -n demo fr-horizontal -o json | jq '.spec.server.primary.replicas'
3

$ kubectl get petset -n demo fr-horizontal -o json | jq '.spec.replicas'
3

From all the above outputs we can see that the replicas of the ferretdb primary server is 3. That means we have successfully scaled up the replicas of the FerretDB.

Scale Down Replicas

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

Create FerretDBOpsRequest

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

apiVersion: ops.kubedb.com/v1alpha1
kind: FerretDBOpsRequest
metadata:
  name: ferretdb-horizontal-scale-down
  namespace: demo
spec:
  type: HorizontalScaling
  databaseRef:
    name: fr-horizontal
  horizontalScaling:
    primary:
      replicas: 2

Here,

  • spec.databaseRef.name specifies that we are performing horizontal scaling down operation on fr-horizontal ferretdb.
  • spec.type specifies that we are performing HorizontalScaling on our ferretdb.
  • spec.horizontalScaling.primary.replicas specifies the desired primary server replicas after scaling.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2025.3.24/docs/examples/ferretdb/scaling/horizontal-scaling/frops-hscale-down-ops.yaml
ferretdbopsrequest.ops.kubedb.com/ferretdb-horizontal-scale-down created

Verify replicas scaled down successfully

If everything goes well, KubeDB Ops-manager operator will update the replicas of FerretDB object and related PetSet.

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

$ watch kubectl get ferretdbopsrequest -n demo
Every 2.0s: kubectl get ferretdbopsrequest -n demo
NAME                             TYPE                STATUS       AGE
ferretdb-horizontal-scale-down   HorizontalScaling   Successful   40s

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

$ kubectl describe ferretdbopsrequest -n demo ferretdb-horizontal-scale-down
Name:         ferretdb-horizontal-scale-down
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         FerretDBOpsRequest
Metadata:
  Creation Timestamp:  2025-04-08T06:26:09Z
  Generation:          1
  Resource Version:    64829
  UID:                 369e5413-9fa3-47de-b491-f7f7568a45c1
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  fr-horizontal
  Horizontal Scaling:
    Primary:
      Replicas:  2
  Type:          HorizontalScaling
Status:
  Conditions:
    Last Transition Time:  2025-04-08T06:26:09Z
    Message:               FerretDB ops-request has started to horizontally scaling the nodes
    Observed Generation:   1
    Reason:                HorizontalScaling
    Status:                True
    Type:                  HorizontalScaling
    Last Transition Time:  2025-04-08T06:26:12Z
    Message:               Successfully paused database
    Observed Generation:   1
    Reason:                DatabasePauseSucceeded
    Status:                True
    Type:                  DatabasePauseSucceeded
    Last Transition Time:  2025-04-08T06:26:27Z
    Message:               Successfully Scaled Down Node
    Observed Generation:   1
    Reason:                HorizontalScaleDown
    Status:                True
    Type:                  HorizontalScaleDown
    Last Transition Time:  2025-04-08T06:26:17Z
    Message:               patch petset; ConditionStatus:True; PodName:fr-horizontal-2
    Observed Generation:   1
    Status:                True
    Type:                  PatchPetset--fr-horizontal-2
    Last Transition Time:  2025-04-08T06:26:17Z
    Message:               fr-horizontal already has desired replicas
    Observed Generation:   1
    Reason:                HorizontalScale
    Status:                True
    Type:                  HorizontalScale
    Last Transition Time:  2025-04-08T06:26:22Z
    Message:               get pod; ConditionStatus:True; PodName:fr-horizontal-2
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--fr-horizontal-2
    Last Transition Time:  2025-04-08T06:26:27Z
    Message:               Successfully updated FerretDB
    Observed Generation:   1
    Reason:                UpdateDatabase
    Status:                True
    Type:                  UpdateDatabase
    Last Transition Time:  2025-04-08T06:26:27Z
    Message:               Successfully completed the HorizontalScaling for FerretDB
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                                                       Age   From                         Message
  ----     ------                                                       ----  ----                         -------
  Normal   Starting                                                     43s   KubeDB Ops-manager Operator  Start processing for FerretDBOpsRequest: demo/ferretdb-horizontal-scale-down
  Normal   Starting                                                     43s   KubeDB Ops-manager Operator  Pausing FerretDB database: demo/fr-horizontal
  Normal   Successful                                                   43s   KubeDB Ops-manager Operator  Successfully paused FerretDB database: demo/fr-horizontal for FerretDBOpsRequest: ferretdb-horizontal-scale-down
  Warning  patch petset; ConditionStatus:True; PodName:fr-horizontal-2  35s   KubeDB Ops-manager Operator  patch petset; ConditionStatus:True; PodName:fr-horizontal-2
  Warning  get pod; ConditionStatus:True; PodName:fr-horizontal-2       30s   KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:fr-horizontal-2
  Normal   HorizontalScaleDown                                          25s   KubeDB Ops-manager Operator  Successfully Scaled Down Node
  Normal   UpdateDatabase                                               25s   KubeDB Ops-manager Operator  Successfully updated FerretDB
  Normal   Starting                                                     25s   KubeDB Ops-manager Operator  Resuming FerretDB database: demo/fr-horizontal
  Normal   Successful                                                   25s   KubeDB Ops-manager Operator  Successfully resumed FerretDB database: demo/fr-horizontal for FerretDBOpsRequest: ferretdb-horizontal-scale-down

Now, we are going to verify the number of replicas this ferretdb has from the FerretDB object, number of pods the petset have,

$ kubectl get fr -n demo fr-horizontal -o json | jq '.spec.server.primary.replicas'
2

$ kubectl get petset -n demo fr-horizontal -o json | jq '.spec.replicas'
2

From all the above outputs we can see that the replicas of the ferretdb is 2. That means we have successfully scaled up the replicas of the FerretDB.

Cleaning Up

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

kubectl delete mg -n fr-horizontal
kubectl delete ferretdbopsrequest -n demo ferretdb-horizontal-scale-down

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