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Druid Horizontal Scaling

This guide will give an overview on how KubeDB Ops-manager operator scales up or down Druid cluster replicas of various component such as Coordinators, Overlords, Historicals, MiddleManager, Brokers and Routers.

Before You Begin

• You should be familiar with the following KubeDB concepts:
  • Druid
  • DruidOpsRequest

How Horizontal Scaling Process Works

The following diagram shows how KubeDB Ops-manager operator scales up or down Druid 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 Druid Custom Resource (CR).

2. KubeDB Provisioner operator watches the Druid CR.

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

4. Then, in order to scale the various components (i.e. Coordinators, Overlords, Historicals, MiddleManagers, Brokers, Routers) of the Druid cluster, the user creates a DruidOpsRequest CR with desired information.

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

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

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

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

9. After the successful scaling of the Druid replicas, the KubeDB Ops-manager operator resumes the Druid 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 Druid cluster using DruidOpsRequest CRD.