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MongoDB Horizontal Scaling

This guide will give an overview on how KubeDB Ops-manager operator scales up or down MongoDB database replicas of various component such as ReplicaSet, Shard, ConfigServer, Mongos, etc.

Before You Begin

• You should be familiar with the following KubeDB concepts:
  • MongoDB
  • MongoDBOpsRequest

How Horizontal Scaling Process Works

The following diagram shows how KubeDB Ops-manager operator scales up or down MongoDB database components. Open the image in a new tab to see the enlarged version.

  

The Horizontal scaling process consists of the following steps:

1. At first, a user creates a MongoDB Custom Resource (CR).

2. KubeDB Provisioner operator watches the MongoDB CR.

3. When the operator finds a MongoDB CR, it creates required number of StatefulSets and related necessary stuff like secrets, services, etc.

4. Then, in order to scale the various components (ie. ReplicaSet, Shard, ConfigServer, Mongos, etc.) of the MongoDB database the user creates a MongoDBOpsRequest CR with desired information.

5. KubeDB Ops-manager operator watches the MongoDBOpsRequest CR.

6. When it finds a MongoDBOpsRequest CR, it halts the MongoDB object which is referred from the MongoDBOpsRequest. So, the KubeDB Provisioner operator doesn’t perform any operations on the MongoDB object during the horizontal scaling process.

7. Then the KubeDB Ops-manager operator will scale the related StatefulSet Pods to reach the expected number of replicas defined in the MongoDBOpsRequest CR.

8. After the successfully scaling the replicas of the related StatefulSet Pods, the KubeDB Ops-manager operator updates the number of replicas in the MongoDB object to reflect the updated state.

9. After the successful scaling of the MongoDB replicas, the KubeDB Ops-manager operator resumes the MongoDB object so that the KubeDB Provisioner operator resumes its usual operations.

In the next docs, we are going to show a step by step guide on horizontal scaling of MongoDB database using MongoDBOpsRequest CRD.