New to KubeDB? Please start here.

Autoscaling the Compute Resource of a FerretDB

This guide will show you how to use KubeDB to autoscale compute resources i.e. cpu and memory 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.
Install KubeDB Provisioner, Ops-manager and Autoscaler operator in your cluster following the steps here.
Install Metrics Server from 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.

Autoscaling of FerretDB

Here, we are going to deploy a FerretDB standalone using a supported version by KubeDB operator. Backend postgres of this FerretDB will be internally managed by KubeDB, or you can use any externally managed postgres but in that case you need to create an appbinding yourself. Then we are going to apply FerretDBAutoscaler to set up autoscaling.

Deploy FerretDB

In this section, we are going to deploy a FerretDB with version 1.23.0 Then, in the next section we will set up autoscaling for this ferretdb using FerretDBAutoscaler CRD. Below is the YAML of the FerretDB CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: FerretDB
metadata:
  name: ferretdb-autoscale
  namespace: demo
spec:
  version: "2.0.0"
  server:
    primary:
      podTemplate:
        spec:
          containers:
            - name: ferretdb
              resources:
                requests:
                  cpu: "200m"
                  memory: "300Mi"
                limits:
                  cpu: "200m"
                  memory: "300Mi"
  storage:
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: 500Mi
  deletionPolicy: WipeOut

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2025.3.24/docs/examples/ferretdb/autoscaling/compute/ferretdb-autoscale.yaml
ferretdb.kubedb.com/ferretdb-autoscale created

Now, wait until ferretdb-autoscale has status Ready. i.e,

$ kubectl get fr -n demo
NAME                 NAMESPACE   VERSION   STATUS   AGE
ferretdb-autoscale   demo        2.0.0     Ready    4m9s

Let’s check the FerretDB resources,

$ kubectl get fr -n demo ferretdb-autoscale -o json | jq '.spec.server.primary.podTemplate.spec.containers[0].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 ferretdb.

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

Compute Resource Autoscaling

Here, we are going to set up compute (cpu and memory) autoscaling using a FerretDBAutoscaler Object.

Create FerretDBAutoscaler Object

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

apiVersion: autoscaling.kubedb.com/v1alpha1
kind: FerretDBAutoscaler
metadata:
  name: ferretdb-autoscale-ops
  namespace: demo
spec:
  databaseRef:
    name: ferretdb-autoscale
  compute:
    primary:
      trigger: "On"
      podLifeTimeThreshold: 5m
      resourceDiffPercentage: 20
      minAllowed:
        cpu: 400m
        memory: 400Mi
      maxAllowed:
        cpu: 1
        memory: 1Gi
      controlledResources: ["cpu", "memory"]
      containerControlledValues: "RequestsAndLimits"

Here,

spec.databaseRef.name specifies that we are performing compute resource autoscaling on ferretdb-autoscale.
spec.compute.primary.trigger specifies that compute resource autoscaling is enabled for this ferretdb primary server.
spec.compute.primary.podLifeTimeThreshold specifies the minimum lifetime for at least one of the pod to initiate a vertical scaling.
spec.compute.replicaset.resourceDiffPercentage specifies the minimum resource difference in percentage. The default is 10%. If the difference between current & recommended resource is less than ResourceDiffPercentage, Autoscaler Operator will ignore the updating.
spec.compute.primary.minAllowed specifies the minimum allowed resources for this ferretdb primary server.
spec.compute.primary.maxAllowed specifies the maximum allowed resources for this ferretdb primary server.
spec.compute.primary.controlledResources specifies the resources that are controlled by the autoscaler.
spec.compute.primary.containerControlledValues specifies which resource values should be controlled. The default is “RequestsAndLimits”.
spec.opsRequestOptions contains the options to pass to the created OpsRequest. It has 2 fields. Know more about them here : timeout, apply.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2025.3.24/docs/examples/ferretdb/autoscaling/compute/autoscaler.yaml
ferretdbautoscaler.autoscaling.kubedb.com/ferretdb-autoscaler-ops created

Verify Autoscaling is set up successfully

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

$ kubectl get ferretdbautoscaler -n demo
NAME                   AGE
ferretdb-autoscale-ops   6m55s

$ kubectl describe ferretdbautoscaler ferretdb-autoscale-ops -n demo
Name:         ferretdb-autoscale-ops
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  autoscaling.kubedb.com/v1alpha1
Kind:         FerretDBAutoscaler
Metadata:
  Creation Timestamp:  2025-04-04T10:36:21Z
  Generation:          1
  Resource Version:    8109
  UID:                 4390f7e7-4578-4798-8828-f117d14ec257
Spec:
  Compute:
    Primary:
      Container Controlled Values:  RequestsAndLimits
      Controlled Resources:
        cpu
        memory
      Max Allowed:
        Cpu:     1
        Memory:  1Gi
      Min Allowed:
        Cpu:                     400m
        Memory:                  400Mi
      Pod Life Time Threshold:   5m0s
      Resource Diff Percentage:  20
      Trigger:                   On
  Database Ref:
    Name:  ferretdb-autoscale
  Ops Request Options:
    Apply:  IfReady
Status:
  Checkpoints:
    Cpu Histogram:
      Bucket Weights:
        Index:              0
        Weight:             10000
      Reference Timestamp:  2025-04-04T10:40:00Z
      Total Weight:         0.6481703155444596
    First Sample Start:     2025-04-04T10:36:14Z
    Last Sample Start:      2025-04-04T10:42:11Z
    Last Update Time:       2025-04-04T10:42:25Z
    Memory Histogram:
      Bucket Weights:
        Index:              0
        Weight:             10000
      Reference Timestamp:  2025-04-04T10:40:00Z
      Total Weight:         1.032875715149387
    Ref:
      Container Name:     ferretdb
      Vpa Object Name:    ferretdb-autoscale
    Total Samples Count:  7
    Version:              v3
  Conditions:
    Last Transition Time:  2025-04-04T10:37:25Z
    Message:               Successfully created FerretDBOpsRequest demo/frops-ferretdb-autoscale-u3ro86
    Observed Generation:   1
    Reason:                CreateOpsRequest
    Status:                True
    Type:                  CreateOpsRequest
  Vpas:
    Conditions:
      Last Transition Time:  2025-04-04T10:36:25Z
      Status:                True
      Type:                  RecommendationProvided
    Recommendation:
      Container Recommendations:
        Container Name:  ferretdb
        Lower Bound:
          Cpu:     400m
          Memory:  400Mi
        Target:
          Cpu:     400m
          Memory:  400Mi
        Uncapped Target:
          Cpu:     100m
          Memory:  262144k
        Upper Bound:
          Cpu:     1
          Memory:  1Gi
    Vpa Name:      ferretdb-autoscale
Events:            <none>

So, the ferretdbautoscaler resource is created successfully.

you can see in the Status.VPAs.Recommendation section, that recommendation has been generated for our ferretdb. Our autoscaler operator continuously watches the recommendation generated and creates an ferretdbopsrequest based on the recommendations, if the ferretdb pods are needed to scaled up or down.

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

$ watch kubectl get ferretdbopsrequest -n demo
Every 2.0s: kubectl get ferretdbopsrequest -n demo
NAME                               TYPE              STATUS        AGE
frops-ferretdb-autoscale-u3ro86    VerticalScaling   Progressing   10s

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

$ watch kubectl get ferretdbopsrequest -n demo
Every 2.0s: kubectl get ferretdbopsrequest -n demo
NAME                              TYPE              STATUS       AGE
frops-ferretdb-autoscale-u3ro86   VerticalScaling   Successful   31s

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 frops-ferretdb-autoscale-u3ro86
Name:         frops-ferretdb-autoscale-u3ro86
Namespace:    demo
Labels:       app.kubernetes.io/component=database
              app.kubernetes.io/instance=ferretdb-autoscale
              app.kubernetes.io/managed-by=kubedb.com
              app.kubernetes.io/name=ferretdbs.kubedb.com
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         FerretDBOpsRequest
Metadata:
  Creation Timestamp:  2025-04-04T10:37:25Z
  Generation:          1
  Owner References:
    API Version:           autoscaling.kubedb.com/v1alpha1
    Block Owner Deletion:  true
    Controller:            true
    Kind:                  FerretDBAutoscaler
    Name:                  ferretdb-autoscale-ops
    UID:                   4390f7e7-4578-4798-8828-f117d14ec257
  Resource Version:        8019
  UID:                     8ec170d0-86fa-4de6-a77d-32a9a9f533e1
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  ferretdb-autoscale
  Type:    VerticalScaling
  Vertical Scaling:
    Primary:
      Resources:
        Limits:
          Cpu:     400m
          Memory:  400Mi
        Requests:
          Cpu:     400m
          Memory:  400Mi
Status:
  Conditions:
    Last Transition Time:  2025-04-04T10:37:25Z
    Message:               FerretDB ops-request has started to vertically scaling the FerretDB nodes
    Observed Generation:   1
    Reason:                VerticalScaling
    Status:                True
    Type:                  VerticalScaling
    Last Transition Time:  2025-04-04T10:37:28Z
    Message:               Successfully paused database
    Observed Generation:   1
    Reason:                DatabasePauseSucceeded
    Status:                True
    Type:                  DatabasePauseSucceeded
    Last Transition Time:  2025-04-04T10:37:28Z
    Message:               Successfully updated PetSets Resources
    Observed Generation:   1
    Reason:                UpdatePetSets
    Status:                True
    Type:                  UpdatePetSets
    Last Transition Time:  2025-04-04T10:37:33Z
    Message:               get pod; ConditionStatus:True; PodName:ferretdb-autoscale-0
    Observed Generation:   1
    Status:                True
    Type:                  GetPod--ferretdb-autoscale-0
    Last Transition Time:  2025-04-04T10:37:33Z
    Message:               evict pod; ConditionStatus:True; PodName:ferretdb-autoscale-0
    Observed Generation:   1
    Status:                True
    Type:                  EvictPod--ferretdb-autoscale-0
    Last Transition Time:  2025-04-04T10:37:38Z
    Message:               check pod running; ConditionStatus:True; PodName:ferretdb-autoscale-0
    Observed Generation:   1
    Status:                True
    Type:                  CheckPodRunning--ferretdb-autoscale-0
    Last Transition Time:  2025-04-04T10:37:43Z
    Message:               Successfully Restarted Pods With Resources
    Observed Generation:   1
    Reason:                RestartPods
    Status:                True
    Type:                  RestartPods
    Last Transition Time:  2025-04-04T10:37:43Z
    Message:               Successfully completed the VerticalScaling for FerretDB
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type     Reason                                                                 Age   From                         Message
  ----     ------                                                                 ----  ----                         -------
  Normal   Starting                                                               14m   KubeDB Ops-manager Operator  Start processing for FerretDBOpsRequest: demo/frops-ferretdb-autoscale-u3ro86
  Normal   Starting                                                               14m   KubeDB Ops-manager Operator  Pausing FerretDB database: demo/ferretdb-autoscale
  Normal   Successful                                                             14m   KubeDB Ops-manager Operator  Successfully paused FerretDB database: demo/ferretdb-autoscale for FerretDBOpsRequest: frops-ferretdb-autoscale-u3ro86
  Normal   UpdatePetSets                                                          14m   KubeDB Ops-manager Operator  Successfully updated PetSets Resources
  Normal   UpdatePetSets                                                          14m   KubeDB Ops-manager Operator  Successfully updated PetSets Resources
  Warning  get pod; ConditionStatus:True; PodName:ferretdb-autoscale-0            14m   KubeDB Ops-manager Operator  get pod; ConditionStatus:True; PodName:ferretdb-autoscale-0
  Warning  evict pod; ConditionStatus:True; PodName:ferretdb-autoscale-0          14m   KubeDB Ops-manager Operator  evict pod; ConditionStatus:True; PodName:ferretdb-autoscale-0
  Warning  check pod running; ConditionStatus:True; PodName:ferretdb-autoscale-0  14m   KubeDB Ops-manager Operator  check pod running; ConditionStatus:True; PodName:ferretdb-autoscale-0
  Normal   RestartPods                                                            14m   KubeDB Ops-manager Operator  Successfully Restarted Pods With Resources
  Normal   Starting                                                               14m   KubeDB Ops-manager Operator  Resuming FerretDB database: demo/ferretdb-autoscale
  Normal   Successful                                                             14m   KubeDB Ops-manager Operator  Successfully resumed FerretDB database: demo/ferretdb-autoscale for FerretDBOpsRequest: frops-ferretdb-autoscale-u3ro86

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

$ kubectl get ferretdb -n demo ferretdb-autoscale -o json | jq '.spec.podTemplate.spec.containers[0].resources'
{
  "limits": {
    "cpu": "400m",
    "memory": "400Mi"
  },
  "requests": {
    "cpu": "400m",
    "memory": "400Mi"
  }
}

The above output verifies that we have successfully auto-scaled the resources of the FerretDB.

Cleaning Up

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

kubectl delete fr -n demo ferretdb-autoscale
kubectl delete ferretdbautoscaler -n demo ferretdb-autoscale-ops

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