KubeDB

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Volume Expansion of DocumentDB

When a DocumentDB database is provisioned on an expandable StorageClass you can grow its data volumes in place with a DocumentDBOpsRequest of type VolumeExpansion — no backup/restore and no manual PVC editing required. This guide expands a 3-node cluster from 5Gi to 10Gi per replica.

[!IMPORTANT] The StorageClass must allow volume expansion (allowVolumeExpansion: true). This guide uses longhorn, which is expandable. The default local-path StorageClass on many clusters is not expandable — check with kubectl get sc and use an expandable class.

Before You Begin

  • You need a Kubernetes cluster and the kubectl CLI configured to talk to it.
  • Install KubeDB following the steps here.
  • This tutorial uses a namespace called demo (kubectl create ns demo).
  • Deploy a DocumentDB cluster (documentdb-cls-sample) on an expandable StorageClass (longhorn) and wait for it to become Ready.

Note: YAML files used in this tutorial are stored in docs/examples/documentdb folder in GitHub repository kubedb/docs.

PVCs before

$ kubectl get pvc -n demo -l app.kubernetes.io/instance=documentdb-cls-sample \
    -o custom-columns=NAME:.metadata.name,SIZE:.status.capacity.storage,SC:.spec.storageClassName,STATUS:.status.phase
NAME                           SIZE   SC         STATUS
data-documentdb-cls-sample-0   5Gi    longhorn   Bound
data-documentdb-cls-sample-1   5Gi    longhorn   Bound
data-documentdb-cls-sample-2   5Gi    longhorn   Bound

Create the VolumeExpansion OpsRequest

mode: Offline tells the operator to recreate the pods around the resize (the PetSet is deleted and recreated so the larger PVCs are picked up cleanly). The documentdb field carries the new target size:

apiVersion: ops.kubedb.com/v1alpha1
kind: DocumentDBOpsRequest
metadata:
  name: documentdb-cls-volume-expansion
  namespace: demo
spec:
  type: VolumeExpansion
  databaseRef:
    name: documentdb-cls-sample
  volumeExpansion:
    mode: Offline
    documentdb: 10Gi

$ kubectl apply -f cluster-volume-expansion.yaml
documentdbopsrequest.ops.kubedb.com/documentdb-cls-volume-expansion created

$ kubectl get dcops -n demo documentdb-cls-volume-expansion
NAME                              TYPE              STATUS       AGE
documentdb-cls-volume-expansion   VolumeExpansion   Successful   4m49s

The status conditions walk through the offline-expansion mechanics: the operator deletes the PetSet, then for each replica it deletes the pod, expands the PVC, recreates the pod, and waits for it to become ready, before finally recreating the PetSet:

$ kubectl get dcops -n demo documentdb-cls-volume-expansion \
    -o jsonpath='{range .status.conditions[*]}{.type}={.status} :: {.message}{"\n"}{end}'
Running=True :: Volume Expansion is in progress
DeletePetset=True :: delete petset; ConditionStatus:True
IsPvcData-documentdb-cls-sample-0Updated=True :: is pvc data-documentdb-cls-sample-0 updated; ConditionStatus:True
CreatePod=True :: create pod; ConditionStatus:True
IsPodReady=True :: is pod ready; ConditionStatus:True
IsPvcData-documentdb-cls-sample-2Updated=True :: is pvc data-documentdb-cls-sample-2 updated; ConditionStatus:True
IsPvcData-documentdb-cls-sample-1Updated=True :: is pvc data-documentdb-cls-sample-1 updated; ConditionStatus:True
VolumeExpansion=True :: Offline Volume Expansion performed successfully in DocumentDB pods
ReadyPetSets=True :: PetSet is recreated
Successful=True :: Successfully Expanded Volume.

PVCs after

All three data volumes are now 10Gi, and the DocumentDB object’s storage request is updated to match:

$ kubectl get pvc -n demo -l app.kubernetes.io/instance=documentdb-cls-sample \
    -o custom-columns=NAME:.metadata.name,SIZE:.status.capacity.storage,SC:.spec.storageClassName,STATUS:.status.phase
NAME                           SIZE   SC         STATUS
data-documentdb-cls-sample-0   10Gi   longhorn   Bound
data-documentdb-cls-sample-1   10Gi   longhorn   Bound
data-documentdb-cls-sample-2   10Gi   longhorn   Bound

$ kubectl get docdb -n demo documentdb-cls-sample -o jsonpath='{.spec.storage.resources.requests.storage}'
10Gi

The cluster is healthy and serving traffic after the expansion:

$ PASS=$(kubectl get secret -n demo documentdb-cls-sample-auth -o jsonpath='{.data.password}' | base64 -d)
$ kubectl exec -n demo documentdb-cls-sample-0 -c documentdb -- \
    mongosh "mongodb://default_user:${PASS}@localhost:10260/?tls=true&tlsAllowInvalidCertificates=true" \
    --quiet --eval 'db.runCommand({ ping: 1 })'
{ ok: 1 }

Standalone

The same DocumentDBOpsRequest works for a standalone (replicas: 1) instance on an expandable StorageClass — point spec.databaseRef.name at documentdb-sa-sample. On this build standalone instances did not finish bootstrapping (see the Restart guide), so the standalone expansion could not be exercised live; the cluster procedure applies once a standalone instance is healthy.

Cleaning Up

kubectl delete documentdbopsrequest -n demo documentdb-cls-volume-expansion
kubectl delete documentdb -n demo documentdb-cls-sample
kubectl delete ns demo

Next Steps

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