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Storage Autoscaling of a Postgres Cluster

This guide will show you how to use KubeDB to autoscale the storage of a Postgres 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.
Install KubeDB Community, Enterprise and Autoscaler operator in your cluster following the steps here.
Install Metrics Server from here
Install Prometheus from here
You must have a StorageClass that supports volume expansion.
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

Storage Autoscaling of Cluster Database

At first verify that your cluster has a storage class, that supports volume expansion. Let’s check,

$ kubectl get storageclass
NAME                  PROVISIONER             RECLAIMPOLICY   VOLUMEBINDINGMODE      ALLOWVOLUMEEXPANSION   AGE
standard (default)    rancher.io/local-path   Delete          WaitForFirstConsumer   false                  79m
topolvm-provisioner   topolvm.cybozu.com      Delete          WaitForFirstConsumer   true                   78m

We can see from the output the topolvm-provisioner storage class has ALLOWVOLUMEEXPANSION field as true. So, this storage class supports volume expansion. We can use it. You can install topolvm from here

Now, we are going to deploy a Postgres cluster using a supported version by KubeDB operator. Then we are going to apply PostgresAutoscaler to set up autoscaling.

Deploy Postgres Cluster

In this section, we are going to deploy a Postgres cluster database with version 16.1. Then, in the next section we will set up autoscaling for this database using PostgresAutoscaler CRD. Below is the YAML of the Postgres CR that we are going to create,

If you want to autoscale Postgres Standalone, Just remove the spec.Replicas from the below yaml and rest of the steps are same.

apiVersion: kubedb.com/v1
kind: Postgres
metadata:
  name: ha-postgres
  namespace: demo
spec:
  version: "16.1"
  replicas: 3
  storageType: Durable
  storage:
    storageClassName: "topolvm-provisioner"
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 1Gi
  deletionPolicy: WipeOut

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

$ kubectl create -f https://github.com/kubedb/docs/raw/v2024.11.8-rc.0/docs/examples/postgres/autoscaler/storage/ha-postgres.yaml
postgres.kubedb.com/ha-postgres created

Now, wait until ha-postgres has status Ready. i.e,

$ kubectl get postgres -n demo
NAME             VERSION   STATUS   AGE
ha-postgres        16.1    Ready    3m46s

Let’s check volume size from petset, and from the persistent volume,

$ kubectl get sts -n demo ha-postgres -o json | jq '.spec.volumeClaimTemplates[].spec.resources.requests.storage'
"1Gi"

$ kubectl get pv -n demo
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                        STORAGECLASS          REASON   AGE
pvc-43266d76-f280-4cca-bd78-d13660a84db9   1Gi        RWO            Delete           Bound    demo/data-ha-postgres-2   topolvm-provisioner            57s
pvc-4a509b05-774b-42d9-b36d-599c9056af37   1Gi        RWO            Delete           Bound    demo/data-ha-postgres-0   topolvm-provisioner            58s
pvc-c27eee12-cd86-4410-b39e-b1dd735fc14d   1Gi        RWO            Delete           Bound    demo/data-ha-postgres-1   topolvm-provisioner            57s

You can see the petset has 1GB storage, and the capacity of all the persistent volume is also 1GB.

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

Storage Autoscaling

Here, we are going to set up storage autoscaling using a PostgresAutoscaler Object.

Create PostgresAutoscaler Object

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

apiVersion: autoscaling.kubedb.com/v1alpha1
kind: PostgresAutoscaler
metadata:
  name: pg-as-st
  namespace: demo
spec:
  databaseRef:
    name: ha-postgres
  storage:
    postgres:
      trigger: "On"
      usageThreshold: 20
      scalingThreshold: 20
      expansionMode: "Online"

Here,

spec.databaseRef.name specifies that we are performing vertical scaling operation on ha-postgres database.
spec.storage.postgres.trigger specifies that storage autoscaling is enabled for this database.
spec.storage.postgres.usageThreshold specifies storage usage threshold, if storage usage exceeds 20% then storage autoscaling will be triggered.
spec.storage.postgres.scalingThreshold specifies the scaling threshold. Storage will be scaled to 20% of the current amount.
spec.storage.postgres.expansionMode specifies the expansion mode of volume expansion PostgresOpsRequest created by PostgresAutoscaler. topolvm-provisioner supports online volume expansion so here expansionMode is set as “Online”.

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

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2024.11.8-rc.0/docs/examples/postgres/autoscaler/storage/pgas-storage.yaml
postgresautoscaler.autoscaling.kubedb.com/pg-as-st created

Storage Autoscaling is set up successfully

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

$ kubectl get postgresautoscaler -n demo
NAME           AGE
pg-as-st   33s

$ kubectl describe postgresautoscaler pg-as-st -n demo
Name:         pg-as-st
Namespace:    demo
Labels:       <none>
Annotations:  API Version:  autoscaling.kubedb.com/v1alpha1
Kind:         PostgresAutoscaler
Metadata:
  Creation Timestamp:  2022-01-14T06:08:02Z
  Generation:          1
  Managed Fields:
    ...
  Resource Version:  24009
  UID:               4f45a3b3-fc72-4d04-b52c-a770944311f6
Spec:
  Database Ref:
    Name:  ha-postgres
  Storage:
    Mariadb:
      Scaling Threshold:  20
      Trigger:            On
      Usage Threshold:    20
Events:                   <none>

So, the postgresautoscaler resource is created successfully.

Now, for this demo, we are going to manually fill up the persistent volume to exceed the usageThreshold using dd command to see if storage autoscaling is working or not.

Let’s exec into the database pod and fill the database volume(/var/pv/data) using the following commands:

$ kubectl exec -it -n demo ha-postgres-0 -- bash
root@ha-postgres-0:/ df -h /var/pv/data
Filesystem                                         Size  Used Avail Use% Mounted on
/dev/topolvm/57cd4330-784f-42c1-bf8e-e743241df164 1014M  357M  658M  36% /var/pv/data
root@ha-postgres-0:/ dd if=/dev/zero of=/var/pv/data/file.img bs=500M count=1
1+0 records in
1+0 records out
524288000 bytes (524 MB, 500 MiB) copied, 0.340877 s, 1.5 GB/s
root@ha-postgres-0:/ df -h /var/pv/data
Filesystem                                         Size  Used Avail Use% Mounted on
/dev/topolvm/57cd4330-784f-42c1-bf8e-e743241df164 1014M  857M  158M  85% /var/pv/data

So, from the above output we can see that the storage usage is 83%, which exceeded the usageThreshold 20%.

Let’s watch the postgresopsrequest in the demo namespace to see if any postgresopsrequest object is created. After some time you’ll see that a postgresopsrequest of type VolumeExpansion will be created based on the scalingThreshold.

$ kubectl get postgresopsrequest -n demo
NAME                         TYPE              STATUS        AGE
pgops-ha-postgres-xojkua   VolumeExpansion   Progressing   15s

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

$ kubectl get postgresopsrequest -n demo
NAME                         TYPE              STATUS       AGE
pgops-ha-postgres-xojkua   VolumeExpansion   Successful   97s

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

$ kubectl describe postgresopsrequest -n demo pgops-ha-postgres-xojkua
Name:         pgops-ha-postgres-xojkua
Namespace:    demo
Labels:       app.kubernetes.io/component=database
              app.kubernetes.io/instance=ha-postgres
              app.kubernetes.io/managed-by=kubedb.com
              app.kubernetes.io/name=postgress.kubedb.com
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         PostgresOpsRequest
Metadata:
  Creation Timestamp:  2022-01-14T06:13:10Z
  Generation:          1
  Managed Fields: ...
  Owner References:
    API Version:           autoscaling.kubedb.com/v1alpha1
    Block Owner Deletion:  true
    Controller:            true
    Kind:                  PostgresAutoscaler
    Name:                  pg-as-st
    UID:                   4f45a3b3-fc72-4d04-b52c-a770944311f6
  Resource Version:        25557
  UID:                     90763a49-a03f-407c-a233-fb20c4ab57d7
Spec:
  Database Ref:
    Name:  ha-postgres
  Type:    VolumeExpansion
  Volume Expansion:
    Mariadb:  1594884096
Status:
  Conditions:
    Last Transition Time:  2022-01-14T06:13:10Z
    Message:               Controller has started to Progress the PostgresOpsRequest: demo/mops-ha-postgres-xojkua
    Observed Generation:   1
    Reason:                OpsRequestProgressingStarted
    Status:                True
    Type:                  Progressing
    Last Transition Time:  2022-01-14T06:14:25Z
    Message:               Volume Expansion performed successfully in Postgres pod for PostgresOpsRequest: demo/mops-ha-postgres-xojkua
    Observed Generation:   1
    Reason:                SuccessfullyVolumeExpanded
    Status:                True
    Type:                  VolumeExpansion
    Last Transition Time:  2022-01-14T06:14:25Z
    Message:               Controller has successfully expand the volume of Postgres demo/mops-ha-postgres-xojkua
    Observed Generation:   1
    Reason:                OpsRequestProcessedSuccessfully
    Status:                True
    Type:                  Successful
  Observed Generation:     3
  Phase:                   Successful
Events:
  Type    Reason      Age    From                        Message
  ----    ------      ----   ----                        -------
  Normal  Starting    2m58s  KubeDB Enterprise Operator  Start processing for PostgresOpsRequest: demo/mops-ha-postgres-xojkua
  Normal  Starting    2m58s  KubeDB Enterprise Operator  Pausing Postgres databse: demo/ha-postgres
  Normal  Successful  2m58s  KubeDB Enterprise Operator  Successfully paused Postgres database: demo/ha-postgres for PostgresOpsRequest: mops-ha-postgres-xojkua
  Normal  Successful  103s   KubeDB Enterprise Operator  Volume Expansion performed successfully in Postgres pod for PostgresOpsRequest: demo/mops-ha-postgres-xojkua
  Normal  Starting    103s   KubeDB Enterprise Operator  Updating Postgres storage
  Normal  Successful  103s   KubeDB Enterprise Operator  Successfully Updated Postgres storage
  Normal  Starting    103s   KubeDB Enterprise Operator  Resuming Postgres database: demo/ha-postgres
  Normal  Successful  103s   KubeDB Enterprise Operator  Successfully resumed Postgres database: demo/ha-postgres
  Normal  Successful  103s   KubeDB Enterprise Operator  Controller has Successfully expand the volume of Postgres: demo/ha-postgres

Now, we are going to verify from the Petset, and the Persistent Volume whether the volume of the cluster database has expanded to meet the desired state, Let’s check,

$ kubectl get sts -n demo ha-postgres -o json | jq '.spec.volumeClaimTemplates[].spec.resources.requests.storage'
"1594884096"
$ kubectl get pv -n demo
NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                        STORAGECLASS          REASON   AGE
pvc-43266d76-f280-4cca-bd78-d13660a84db9   2Gi        RWO            Delete           Bound    demo/data-ha-postgres-2   topolvm-provisioner            23m
pvc-4a509b05-774b-42d9-b36d-599c9056af37   2Gi        RWO            Delete           Bound    demo/data-ha-postgres-0   topolvm-provisioner            24m
pvc-c27eee12-cd86-4410-b39e-b1dd735fc14d   2Gi        RWO            Delete           Bound    demo/data-ha-postgres-1   topolvm-provisioner            23m

The above output verifies that we have successfully autoscaled the volume of the Postgres cluster database.

Cleaning Up

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

kubectl delete postgres -n demo ha-postgres
kubectl delete postgresautoscaler -n demo pg-as-st
kubectl delete ns demo

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