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Storage Autoscaling of a MongoDB Replicaset Database
This guide will show you how to use KubeDB to autoscale the storage 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.Install
KubeDBProvisioner, Ops-manager and Autoscaler operator in your cluster following the steps here.Install
Metrics Serverfrom hereInstall Prometheus from here
You must have a
StorageClassthat supports volume expansion.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.
Storage Autoscaling of 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) rancher.io/local-path Delete WaitForFirstConsumer false 9h
topolvm-provisioner topolvm.cybozu.com Delete WaitForFirstConsumer true 9h
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 MongoDB replicaset using a supported version by KubeDB operator. Then we are going to apply MongoDBAutoscaler to set up autoscaling.
Deploy MongoDB replicaset
In this section, we are going to deploy a MongoDB replicaset database with version 4.4.26. Then, in the next section we will set up autoscaling for this database using MongoDBAutoscaler CRD. Below is the YAML of the MongoDB CR that we are going to create,
apiVersion: kubedb.com/v1alpha2
kind: MongoDB
metadata:
name: mg-rs
namespace: demo
spec:
version: "4.4.26"
replicaSet:
name: "replicaset"
replicas: 3
storageType: Durable
storage:
storageClassName: topolvm-provisioner
resources:
requests:
storage: 1Gi
terminationPolicy: WipeOut
Let’s create the MongoDB CRO we have shown above,
$ kubectl create -f https://github.com/kubedb/docs/raw/v2023.12.28/docs/examples/mongodb/autoscaling/storage/mg-rs.yaml
mongodb.kubedb.com/mg-rs created
Now, wait until mg-rs has status Ready. i.e,
$ kubectl get mg -n demo
NAME VERSION STATUS AGE
mg-rs 4.4.26 Ready 2m53s
Let’s check volume size from statefulset, and from the persistent volume,
$ kubectl get sts -n demo mg-rs -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-b16daa50-83fc-4d25-b553-4a25f13166d5 1Gi RWO Delete Bound demo/datadir-mg-rs-0 topolvm-provisioner 2m12s
pvc-d4616bef-359d-4b73-ab9f-38c24aaaec8c 1Gi RWO Delete Bound demo/datadir-mg-rs-1 topolvm-provisioner 61s
pvc-ead21204-3dc7-453c-8121-d2fe48b1c3e2 1Gi RWO Delete Bound demo/datadir-mg-rs-2 topolvm-provisioner 18s
You can see the statefulset has 1GB storage, and the capacity of all the persistent volume is also 1GB.
We are now ready to apply the MongoDBAutoscaler CRO to set up storage autoscaling for this database.
Storage Autoscaling
Here, we are going to set up storage autoscaling using a MongoDBAutoscaler Object.
Create MongoDBAutoscaler Object
In order to set up vertical autoscaling for this replicaset database, we have to create a MongoDBAutoscaler CRO with our desired configuration. Below is the YAML of the MongoDBAutoscaler object that we are going to create,
apiVersion: autoscaling.kubedb.com/v1alpha1
kind: MongoDBAutoscaler
metadata:
name: mg-as-rs
namespace: demo
spec:
databaseRef:
name: mg-rs
storage:
replicaSet:
trigger: "On"
usageThreshold: 60
scalingThreshold: 50
Here,
spec.databaseRef.namespecifies that we are performing vertical scaling operation onmg-rsdatabase.spec.storage.replicaSet.triggerspecifies that storage autoscaling is enabled for this database.spec.storage.replicaSet.usageThresholdspecifies storage usage threshold, if storage usage exceeds60%then storage autoscaling will be triggered.spec.storage.replicaSet.scalingThresholdspecifies the scaling threshold. Storage will be scaled to50%of the current amount.- It has another field
spec.storage.replicaSet.expansionModeto set the opsRequest volumeExpansionMode, which support two values:Online&Offline. Default value isOnline.
Let’s create the MongoDBAutoscaler CR we have shown above,
$ kubectl apply -f https://github.com/kubedb/docs/raw/v2023.12.28/docs/examples/mongodb/autoscaling/storage/mg-as-rs.yaml
mongodbautoscaler.autoscaling.kubedb.com/mg-as-rs created
Storage Autoscaling is set up successfully
Let’s check that the mongodbautoscaler resource is created successfully,
$ kubectl get mongodbautoscaler -n demo
NAME AGE
mg-as-rs 20s
$ kubectl describe mongodbautoscaler mg-as-rs -n demo
Name: mg-as-rs
Namespace: demo
Labels: <none>
Annotations: <none>
API Version: autoscaling.kubedb.com/v1alpha1
Kind: MongoDBAutoscaler
Metadata:
Creation Timestamp: 2021-03-08T14:11:46Z
Generation: 1
Managed Fields:
API Version: autoscaling.kubedb.com/v1alpha1
Fields Type: FieldsV1
fieldsV1:
f:metadata:
f:annotations:
.:
f:kubectl.kubernetes.io/last-applied-configuration:
f:spec:
.:
f:databaseRef:
.:
f:name:
f:storage:
.:
f:replicaSet:
.:
f:scalingThreshold:
f:trigger:
f:usageThreshold:
Manager: kubectl-client-side-apply
Operation: Update
Time: 2021-03-08T14:11:46Z
Resource Version: 152149
Self Link: /apis/autoscaling.kubedb.com/v1alpha1/namespaces/demo/mongodbautoscalers/mg-as-rs
UID: a0dab64d-e7c4-4819-8ffe-360c70231577
Spec:
Database Ref:
Name: mg-rs
Storage:
Replica Set:
Scaling Threshold: 50
Trigger: On
Usage Threshold: 60
Events: <none>
So, the mongodbautoscaler 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 using the following commands:
$ kubectl exec -it -n demo mg-rs-0 -- bash
root@mg-rs-0:/# df -h /data/db
Filesystem Size Used Avail Use% Mounted on
/dev/topolvm/760cb655-91fe-4497-ab4a-a771aa53ece4 1014M 335M 680M 33% /data/db
root@mg-rs-0:/# dd if=/dev/zero of=/data/db/file.img bs=500M count=1
1+0 records in
1+0 records out
524288000 bytes (524 MB, 500 MiB) copied, 0.482378 s, 1.1 GB/s
root@mg-rs-0:/# df -h /data/db
Filesystem Size Used Avail Use% Mounted on
/dev/topolvm/760cb655-91fe-4497-ab4a-a771aa53ece4 1014M 835M 180M 83% /data/db
So, from the above output we can see that the storage usage is 83%, which exceeded the usageThreshold 60%.
Let’s watch the mongodbopsrequest in the demo namespace to see if any mongodbopsrequest object is created. After some time you’ll see that a mongodbopsrequest of type VolumeExpansion will be created based on the scalingThreshold.
$ watch kubectl get mongodbopsrequest -n demo
Every 2.0s: kubectl get mongodbopsrequest -n demo
NAME TYPE STATUS AGE
mops-mg-rs-mft11m VolumeExpansion Progressing 10s
Let’s wait for the ops request to become successful.
$ watch kubectl get mongodbopsrequest -n demo
Every 2.0s: kubectl get mongodbopsrequest -n demo
NAME TYPE STATUS AGE
mops-mg-rs-mft11m VolumeExpansion Successful 97s
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-mg-rs-mft11m
Name: mops-mg-rs-mft11m
Namespace: demo
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mg-rs
app.kubernetes.io/managed-by=kubedb.com
app.kubernetes.io/name=mongodbs.kubedb.com
Annotations: <none>
API Version: ops.kubedb.com/v1alpha1
Kind: MongoDBOpsRequest
Metadata:
Creation Timestamp: 2021-03-08T14:15:52Z
Generation: 1
Managed Fields:
API Version: ops.kubedb.com/v1alpha1
Fields Type: FieldsV1
fieldsV1:
f:metadata:
f:labels:
.:
f:app.kubernetes.io/component:
f:app.kubernetes.io/instance:
f:app.kubernetes.io/managed-by:
f:app.kubernetes.io/name:
f:ownerReferences:
f:spec:
.:
f:databaseRef:
.:
f:name:
f:type:
f:volumeExpansion:
.:
f:replicaSet:
Manager: kubedb-autoscaler
Operation: Update
Time: 2021-03-08T14:15:52Z
API Version: ops.kubedb.com/v1alpha1
Fields Type: FieldsV1
fieldsV1:
f:status:
.:
f:conditions:
f:observedGeneration:
f:phase:
Manager: kubedb-enterprise
Operation: Update
Time: 2021-03-08T14:15:52Z
Owner References:
API Version: autoscaling.kubedb.com/v1alpha1
Block Owner Deletion: true
Controller: true
Kind: MongoDBAutoscaler
Name: mg-as-rs
UID: a0dab64d-e7c4-4819-8ffe-360c70231577
Resource Version: 153496
Self Link: /apis/ops.kubedb.com/v1alpha1/namespaces/demo/mongodbopsrequests/mops-mg-rs-mft11m
UID: 84567b84-6de4-4658-b0d2-2c374e03e63d
Spec:
Database Ref:
Name: mg-rs
Type: VolumeExpansion
Volume Expansion:
Replica Set: 1594884096
Status:
Conditions:
Last Transition Time: 2021-03-08T14:15:52Z
Message: MongoDB ops request is expanding volume of database
Observed Generation: 1
Reason: VolumeExpansion
Status: True
Type: VolumeExpansion
Last Transition Time: 2021-03-08T14:17:02Z
Message: Successfully Expanded Volume
Observed Generation: 1
Reason: ReplicasetVolumeExpansion
Status: True
Type: ReplicasetVolumeExpansion
Last Transition Time: 2021-03-08T14:17:07Z
Message: Successfully Expanded Volume
Observed Generation: 1
Reason:
Status: True
Type:
Last Transition Time: 2021-03-08T14:17:12Z
Message: StatefulSet is recreated
Observed Generation: 1
Reason: ReadyStatefulSets
Status: True
Type: ReadyStatefulSets
Last Transition Time: 2021-03-08T14:17:12Z
Message: Successfully Expanded Volume
Observed Generation: 1
Reason: Successful
Status: True
Type: Successful
Observed Generation: 1
Phase: Successful
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal PauseDatabase 2m36s KubeDB Ops-manager operator Pausing MongoDB demo/mg-rs
Normal PauseDatabase 2m36s KubeDB Ops-manager operator Successfully paused MongoDB demo/mg-rs
Normal ReplicasetVolumeExpansion 86s KubeDB Ops-manager operator Successfully Expanded Volume
Normal 81s KubeDB Ops-manager operator Successfully Expanded Volume
Normal ResumeDatabase 81s KubeDB Ops-manager operator Resuming MongoDB demo/mg-rs
Normal ResumeDatabase 81s KubeDB Ops-manager operator Successfully resumed MongoDB demo/mg-rs
Normal ReadyStatefulSets 76s KubeDB Ops-manager operator StatefulSet is recreated
Normal Successful 76s KubeDB Ops-manager operator Successfully Expanded Volume
Now, we are going to verify from the Statefulset, and the Persistent Volume whether the volume of the replicaset database has expanded to meet the desired state, Let’s check,
$ kubectl get sts -n demo mg-rs -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-b16daa50-83fc-4d25-b553-4a25f13166d5 2Gi RWO Delete Bound demo/datadir-mg-rs-0 topolvm-provisioner 11m
pvc-d4616bef-359d-4b73-ab9f-38c24aaaec8c 2Gi RWO Delete Bound demo/datadir-mg-rs-1 topolvm-provisioner 10m
pvc-ead21204-3dc7-453c-8121-d2fe48b1c3e2 2Gi RWO Delete Bound demo/datadir-mg-rs-2 topolvm-provisioner 9m52s
The above output verifies that we have successfully autoscaled the volume of the MongoDB replicaset database.
Cleaning Up
To clean up the Kubernetes resources created by this tutorial, run:
kubectl delete mg -n demo mg-rs
kubectl delete mongodbautoscaler -n demo mg-as-rs