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MongoDB Replicaset Volume Expansion
This guide will show you how to use KubeDB Ops-manager operator to expand the volume of a MongoDB Replicaset database.
Before You Begin
At first, you need to have a Kubernetes cluster, and the
kubectlcommand-line tool must be configured to communicate with your cluster.You must have a
StorageClassthat supports volume expansion.Install
KubeDBProvisioner and Ops-manager operator in your cluster following the steps here.You should be familiar with the following
KubeDBconcepts:
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.
Expand Volume of Replicaset
Here, we are going to deploy a MongoDB replicaset using a supported version by KubeDB operator. Then we are going to apply MongoDBOpsRequest to expand its volume.
Prepare MongoDB Replicaset 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) kubernetes.io/gce-pd Delete Immediate true 2m49s
We can see from the output the standard storage class has ALLOWVOLUMEEXPANSION field as true. So, this storage class supports volume expansion. We can use it.
Now, we are going to deploy a MongoDB replicaSet database with version 3.6.8.
Deploy MongoDB
In this section, we are going to deploy a MongoDB Replicaset database with 1GB volume. Then, in the next section we will expand its volume to 2GB using MongoDBOpsRequest CRD. Below is the YAML of the MongoDB CR that we are going to create,
apiVersion: kubedb.com/v1alpha2
kind: MongoDB
metadata:
name: mg-replicaset
namespace: demo
spec:
version: "4.2.3"
replicaSet:
name: "replicaset"
replicas: 3
storageType: Durable
storage:
storageClassName: "standard"
accessModes:
- ReadWriteOnce
resources:
requests:
storage: 1Gi
Let’s create the MongoDB CR we have shown above,
$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.08.18/docs/examples/mongodb/volume-expansion/mg-replicaset.yaml
mongodb.kubedb.com/mg-replicaset created
Now, wait until mg-replicaset has status Ready. i.e,
$ kubectl get mg -n demo
NAME VERSION STATUS AGE
mg-replicaset 4.2.3 Ready 10m
Let’s check volume size from statefulset, and from the persistent volume,
$ kubectl get sts -n demo mg-replicaset -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-2067c63d-f982-4b66-a008-5e9c3ff6218a 1Gi RWO Delete Bound demo/datadir-mg-replicaset-0 standard 10m
pvc-9db1aeb0-f1af-4555-93a3-0ca754327751 1Gi RWO Delete Bound demo/datadir-mg-replicaset-2 standard 9m45s
pvc-d38f42a8-50d4-4fa9-82ba-69fc7a464ff4 1Gi RWO Delete Bound demo/datadir-mg-replicaset-1 standard 10m
You can see the statefulset has 1GB storage, and the capacity of all the persistent volumes are also 1GB.
We are now ready to apply the MongoDBOpsRequest CR to expand the volume of this database.
Volume Expansion
Here, we are going to expand the volume of the replicaset database.
Create MongoDBOpsRequest
In order to expand the volume of the database, we have to create a MongoDBOpsRequest CR with our desired volume size. Below is the YAML of the MongoDBOpsRequest CR that we are going to create,
apiVersion: ops.kubedb.com/v1alpha1
kind: MongoDBOpsRequest
metadata:
name: mops-volume-exp-replicaset
namespace: demo
spec:
type: VolumeExpansion
databaseRef:
name: mg-replicaset
volumeExpansion:
replicaSet: 2Gi
Here,
spec.databaseRef.namespecifies that we are performing volume expansion operation onmops-volume-exp-replicasetdatabase.spec.typespecifies that we are performingVolumeExpansionon our database.spec.volumeExpansion.replicaSetspecifies the desired volume size.
Let’s create the MongoDBOpsRequest CR we have shown above,
$ kubectl apply -f https://github.com/kubedb/docs/raw/v2023.08.18/docs/examples/mongodb/volume-expansion/mops-volume-exp-replicaset.yaml
mongodbopsrequest.ops.kubedb.com/mops-volume-exp-replicaset created
Verify MongoDB replicaset volume expanded successfully
If everything goes well, KubeDB Ops-manager operator will update the volume size of MongoDB object and related StatefulSets and Persistent Volumes.
Let’s wait for MongoDBOpsRequest to be Successful. Run the following command to watch MongoDBOpsRequest CR,
$ kubectl get mongodbopsrequest -n demo
Every 2.0s: kubectl get mongodbopsrequest -n demo
NAME TYPE STATUS AGE
mops-volume-exp-replicaset VolumeExpansion Successful 83s
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 expand the volume of the database.
$ kubectl describe mongodbopsrequest -n demo mops-volume-exp-replicaset
Name: mops-volume-exp-replicaset
Namespace: demo
Labels: <none>
Annotations: API Version: ops.kubedb.com/v1alpha1
Kind: MongoDBOpsRequest
Metadata:
Creation Timestamp: 2020-08-25T18:21:18Z
Finalizers:
kubedb.com
Generation: 1
Resource Version: 84084
Self Link: /apis/ops.kubedb.com/v1alpha1/namespaces/demo/mongodbopsrequests/mops-volume-exp-replicaset
UID: 2cec0cd3-4abe-4114-813c-1326f28563cb
Spec:
Database Ref:
Name: mg-replicaset
Type: VolumeExpansion
Volume Expansion:
ReplicaSet: 2Gi
Status:
Conditions:
Last Transition Time: 2020-08-25T18:21:18Z
Message: MongoDB ops request is being processed
Observed Generation: 1
Reason: Scaling
Status: True
Type: Scaling
Last Transition Time: 2020-08-25T18:22:38Z
Message: Successfully updated Storage
Observed Generation: 1
Reason: VolumeExpansion
Status: True
Type: VolumeExpansion
Last Transition Time: 2020-08-25T18:22:38Z
Message: Successfully Resumed mongodb: mg-replicaset
Observed Generation: 1
Reason: ResumeDatabase
Status: True
Type: ResumeDatabase
Last Transition Time: 2020-08-25T18:22:38Z
Message: Successfully completed the modification process
Observed Generation: 1
Reason: Successful
Status: True
Type: Successful
Observed Generation: 1
Phase: Successful
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal VolumeExpansion 3m11s KubeDB Ops-manager operator Successfully Updated Storage
Normal ResumeDatabase 3m11s KubeDB Ops-manager operator Resuming MongoDB
Normal ResumeDatabase 3m11s KubeDB Ops-manager operator Successfully Resumed mongodb
Normal Successful 3m11s KubeDB Ops-manager operator Successfully Scaled Database
Now, we are going to verify from the Statefulset, and the Persistent Volumes whether the volume of the database has expanded to meet the desired state, Let’s check,
$ kubectl get sts -n demo mg-replicaset -o json | jq '.spec.volumeClaimTemplates[].spec.resources.requests.storage'
"2Gi"
$ kubectl get pv -n demo
NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE
pvc-2067c63d-f982-4b66-a008-5e9c3ff6218a 2Gi RWO Delete Bound demo/datadir-mg-replicaset-0 standard 19m
pvc-9db1aeb0-f1af-4555-93a3-0ca754327751 2Gi RWO Delete Bound demo/datadir-mg-replicaset-2 standard 18m
pvc-d38f42a8-50d4-4fa9-82ba-69fc7a464ff4 2Gi RWO Delete Bound demo/datadir-mg-replicaset-1 standard 19m
The above output verifies that we have successfully expanded the volume of the MongoDB database.
Cleaning Up
To clean up the Kubernetes resources created by this tutorial, run:
kubectl delete mg -n demo mg-replicaset
kubectl delete mongodbopsrequest -n demo mops-volume-exp-replicaset