Status

Current state: UNDER DISCUSSION

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JIRA: KAFKA-5319

Released: 

Motivation

I want to add a tool to make amounts of replicas and leaders on every brokers balanced.Current kafka server does not provide a function to make cluster balance.When we use console command to create a topic without 'replicaAssignmentOpt' ,kafka server   assigns replicas  by a "replicaAssignment" function . The function spread the replicas evenly among brokers to make cluster balanced.It can not make sure the cluster is balanced.Even though it is balanced,the balanced state will be destroyed.Example:

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So it is necessary to add to add a tool to deal with replica and leader balance. 

 Proposed Changes

We use an algorithm to get a balanced assignment of replicas or leaders,and call ReassignPartitionsCommand to let kafka sever move replicas or change the position of replicas in ARs. 

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1. show-cluster-state         This command print out current cluster balance state.We can use it to learn whether or not the cluster need                             to be balanced

2. leader-balance             This command let amounts of leaders of every brokers make balanced

3. replica-rebalance          This command let amounts of replicas and leaders of every brokers make balanced

    

Public Interfaces

Compatibility, Deprecation, and Migration Plan

Rejected Alternatives

We can also use  ReassignPartitionsCommand to move replicas to make replica balance and change the first replica in ARs to make leader balance by manual operation.However it will become more and more difficult with topic and broker increasing.

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