Split Brain with Fencing

Motivation

In the case of zombie leader where the leader is considered dead and the system elects a new leader, we need to make sure the old leader is not running and possibly issuing conflicting commands.

Solution

Put a fence around a previously active leader so that it cannot access cluster resources and hence stop serving any read/write request:

• resource fencing - the system blocks the previously active leader from accessing resources needed to perform essential tasks.

• node fencing - the system stops the previously active leader from accessing all resources.

Applications

HDFS uses fencing to stop the previously active NameNode from accessing cluster resources, thereby stopping it from servicing requests.