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Storage Autoscaling of a MongoDB Sharded Database
This guide will show you how to use KubeDB to autoscale the storage of a MongoDB Sharded 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
KubeDBCommunity, Enterprise and Autoscaler operator in your cluster following the steps here.Install
Metrics Serverfrom hereInstall
Vertical Pod Autoscalerfrom 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 Sharded 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 sharded database using a supported version by KubeDB operator. Then we are going to apply MongoDBAutoscaler to set up autoscaling.
Deploy MongoDB Sharded Database
In this section, we are going to deploy a MongoDB sharded database with version 4.2.3. 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-sh
namespace: demo
spec:
version: "4.2.3"
storageType: Durable
shardTopology:
configServer:
storage:
storageClassName: topolvm-provisioner
resources:
requests:
storage: 1Gi
replicas: 3
mongos:
replicas: 2
shard:
storage:
storageClassName: topolvm-provisioner
resources:
requests:
storage: 1Gi
replicas: 3
shards: 2
terminationPolicy: WipeOut
Let’s create the MongoDB CRO we have shown above,
$ kubectl create -f https://github.com/kubedb/docs/raw/v2021.12.21/docs/examples/mongodb/autoscaling/storage/mg-sh.yaml
mongodb.kubedb.com/mg-sh created
Now, wait until mg-sh has status Ready. i.e,
$ kubectl get mg -n demo
NAME VERSION STATUS AGE
mg-sh 4.2.3 Ready 3m51s
Let’s check volume size from one of the shard statefulset, and from the persistent volume,
$ kubectl get sts -n demo mg-sh-shard0 -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-031836c6-95ae-4015-938c-da183c205828 1Gi RWO Delete Bound demo/datadir-mg-sh-configsvr-0 topolvm-provisioner 5m1s
pvc-2515233f-0f7d-4d0d-8b45-97a3cb9d4488 1Gi RWO Delete Bound demo/datadir-mg-sh-shard0-2 topolvm-provisioner 3m44s
pvc-35f73708-3c11-4ead-a60b-e1679a294b81 1Gi RWO Delete Bound demo/datadir-mg-sh-shard0-0 topolvm-provisioner 5m
pvc-4b329feb-8c92-4605-a37e-c02b3499e311 1Gi RWO Delete Bound demo/datadir-mg-sh-configsvr-2 topolvm-provisioner 3m55s
pvc-52490270-1355-4045-b2a1-872a671ab006 1Gi RWO Delete Bound demo/datadir-mg-sh-configsvr-1 topolvm-provisioner 4m28s
pvc-80dc91d3-f56f-4037-b6e1-f69e13fb434c 1Gi RWO Delete Bound demo/datadir-mg-sh-shard1-1 topolvm-provisioner 4m26s
pvc-c1965a32-7471-4885-ac52-f9eab056d48e 1Gi RWO Delete Bound demo/datadir-mg-sh-shard1-2 topolvm-provisioner 3m57s
pvc-c838a27d-c75d-4caa-9c1d-456af3bfaba0 1Gi RWO Delete Bound demo/datadir-mg-sh-shard1-0 topolvm-provisioner 4m59s
pvc-d47f19be-f206-41c5-a0b1-5022776fea2f 1Gi RWO Delete Bound demo/datadir-mg-sh-shard0-1 topolvm-provisioner 4m25s
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 sharded 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-sh
namespace: demo
spec:
databaseRef:
name: mg-sh
storage:
shard:
trigger: "On"
usageThreshold: 60
scalingThreshold: 50
Here,
spec.databaseRef.namespecifies that we are performing vertical scaling operation onmg-shdatabase.spec.storage.shard.triggerspecifies that storage autoscaling is enabled for this database.spec.storage.shard.usageThresholdspecifies storage usage threshold, if storage usage exceeds60%then storage autoscaling will be triggered.spec.storage.shard.scalingThresholdspecifies the scaling threshold. Storage will be scaled to50%of the current amount.
Note: In this demo we are only setting up the storage autoscaling for the shard pods, that’s why we only specified the shard section of the autoscaler. You can enable autoscaling for configServer pods in the same yaml, by specifying the
spec.configServersection, similar to thespec.shardsection we have configured in this demo.
Let’s create the MongoDBAutoscaler CR we have shown above,
$ kubectl apply -f https://github.com/kubedb/docs/raw/v2021.12.21/docs/examples/mongodb/autoscaling/storage/mg-as-sh.yaml
mongodbautoscaler.autoscaling.kubedb.com/mg-as-sh 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-sh 20s
$ kubectl describe mongodbautoscaler mg-as-sh -n demo
Name: mg-as-sh
Namespace: demo
Labels: <none>
Annotations: <none>
API Version: autoscaling.kubedb.com/v1alpha1
Kind: MongoDBAutoscaler
Metadata:
Creation Timestamp: 2021-03-08T14:26:06Z
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:shard:
.:
f:scalingThreshold:
f:trigger:
f:usageThreshold:
Manager: kubectl-client-side-apply
Operation: Update
Time: 2021-03-08T14:26:06Z
Resource Version: 156292
Self Link: /apis/autoscaling.kubedb.com/v1alpha1/namespaces/demo/mongodbautoscalers/mg-as-sh
UID: 203e332f-bdfe-470f-a429-a7b60c7be2ee
Spec:
Database Ref:
Name: mg-sh
Storage:
Shard:
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 one of 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-sh-shard0-0 -- bash
root@mg-sh-shard0-0:/# df -h /data/db
Filesystem Size Used Avail Use% Mounted on
/dev/topolvm/ad11042f-f4cc-4dfc-9680-2afbbb199d48 1014M 335M 680M 34% /data/db
root@mg-sh-shard0-0:/# 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, 0.595358 s, 881 MB/s
root@mg-sh-shard0-0:/# df -h /data/db
Filesystem Size Used Avail Use% Mounted on
/dev/topolvm/ad11042f-f4cc-4dfc-9680-2afbbb199d48 1014M 837M 178M 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-sh-ba5ikn VolumeExpansion Progressing 41s
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-sh-ba5ikn VolumeExpansion Successful 2m54s
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-sh-ba5ikn
Name: mops-mg-sh-ba5ikn
Namespace: demo
Labels: app.kubernetes.io/component=database
app.kubernetes.io/instance=mg-sh
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: 2021-03-08T14:31:52Z
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:shard:
Manager: kubedb-autoscaler
Operation: Update
Time: 2021-03-08T14:31:52Z
API Version: ops.kubedb.com/v1alpha1
Fields Type: FieldsV1
fieldsV1:
f:status:
.:
f:conditions:
f:observedGeneration:
f:phase:
Manager: kubedb-enterprise
Operation: Update
Time: 2021-03-08T14:31:52Z
Owner References:
API Version: autoscaling.kubedb.com/v1alpha1
Block Owner Deletion: true
Controller: true
Kind: MongoDBAutoscaler
Name: mg-as-sh
UID: 203e332f-bdfe-470f-a429-a7b60c7be2ee
Resource Version: 158488
Self Link: /apis/ops.kubedb.com/v1alpha1/namespaces/demo/mongodbopsrequests/mops-mg-sh-ba5ikn
UID: c56236c2-5b64-4775-ba5a-35727b96a414
Spec:
Database Ref:
Name: mg-sh
Type: VolumeExpansion
Volume Expansion:
Shard: 1594884096
Status:
Conditions:
Last Transition Time: 2021-03-08T14:31:52Z
Message: MongoDB ops request is expanding volume of database
Observed Generation: 1
Reason: VolumeExpansion
Status: True
Type: VolumeExpansion
Last Transition Time: 2021-03-08T14:34:32Z
Message: Successfully Expanded Volume
Observed Generation: 1
Reason: ShardVolumeExpansion
Status: True
Type: ShardVolumeExpansion
Last Transition Time: 2021-03-08T14:34:37Z
Message: Successfully Expanded Volume
Observed Generation: 1
Reason:
Status: True
Type:
Last Transition Time: 2021-03-08T14:34:42Z
Message: StatefulSet is recreated
Observed Generation: 1
Reason: ReadyStatefulSets
Status: True
Type: ReadyStatefulSets
Last Transition Time: 2021-03-08T14:34:42Z
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 3m21s KubeDB Enterprise Operator Pausing MongoDB demo/mg-sh
Normal PauseDatabase 3m21s KubeDB Enterprise Operator Successfully paused MongoDB demo/mg-sh
Normal ShardVolumeExpansion 41s KubeDB Enterprise Operator Successfully Expanded Volume
Normal 36s KubeDB Enterprise Operator Successfully Expanded Volume
Normal ResumeDatabase 36s KubeDB Enterprise Operator Resuming MongoDB demo/mg-sh
Normal ResumeDatabase 36s KubeDB Enterprise Operator Successfully resumed MongoDB demo/mg-sh
Normal ReadyStatefulSets 31s KubeDB Enterprise Operator StatefulSet is recreated
Normal Successful 31s KubeDB Enterprise Operator Successfully Expanded Volume
Now, we are going to verify from the Statefulset, and the Persistent Volume whether the volume of the shard nodes of the database has expanded to meet the desired state, Let’s check,
$ kubectl get sts -n demo mg-sh-shard0 -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-031836c6-95ae-4015-938c-da183c205828 1Gi RWO Delete Bound demo/datadir-mg-sh-configsvr-0 topolvm-provisioner 13m
pvc-2515233f-0f7d-4d0d-8b45-97a3cb9d4488 2Gi RWO Delete Bound demo/datadir-mg-sh-shard0-2 topolvm-provisioner 11m
pvc-35f73708-3c11-4ead-a60b-e1679a294b81 2Gi RWO Delete Bound demo/datadir-mg-sh-shard0-0 topolvm-provisioner 13m
pvc-4b329feb-8c92-4605-a37e-c02b3499e311 1Gi RWO Delete Bound demo/datadir-mg-sh-configsvr-2 topolvm-provisioner 11m
pvc-52490270-1355-4045-b2a1-872a671ab006 1Gi RWO Delete Bound demo/datadir-mg-sh-configsvr-1 topolvm-provisioner 12m
pvc-80dc91d3-f56f-4037-b6e1-f69e13fb434c 2Gi RWO Delete Bound demo/datadir-mg-sh-shard1-1 topolvm-provisioner 12m
pvc-c1965a32-7471-4885-ac52-f9eab056d48e 2Gi RWO Delete Bound demo/datadir-mg-sh-shard1-2 topolvm-provisioner 11m
pvc-c838a27d-c75d-4caa-9c1d-456af3bfaba0 2Gi RWO Delete Bound demo/datadir-mg-sh-shard1-0 topolvm-provisioner 12m
pvc-d47f19be-f206-41c5-a0b1-5022776fea2f 2Gi RWO Delete Bound demo/datadir-mg-sh-shard0-1 topolvm-provisioner 12m
The above output verifies that we have successfully autoscaled the volume of the shard nodes of this MongoDB database.
Cleaning Up
To clean up the Kubernetes resources created by this tutorial, run:
kubectl delete mg -n demo mg-sh
kubectl delete mongodbautoscaler -n demo mg-as-sh