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MongoDB Horizontal Scaling

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

Before You Begin

How Horizontal Scaling Process Works

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

  Horizontal scaling process of MongoDB
Fig: Horizontal scaling process of MongoDB

The Horizontal scaling process consists of the following steps:

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

  2. KubeDB Community 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 Enterprise 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 Community operator doesn’t perform any operations on the MongoDB object during the horizontal scaling process.

  7. Then the KubeDB Enterprise 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 Enterprise 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 Enterprise operator resumes the MongoDB object so that the KubeDB Community 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.