Procedure to change vSAN (cmmds) leader node in a vSAN cluster

Products

• VMware vSAN

Issue/Introduction

This article explains how to change the vSAN (cmmds) leader/master in a vSAN cluster on demand.

Environment

VMware vSAN 7.x

VMware vSAN 8.x

Resolution

To change the vSAN (cmmds) leader in a vSAN cluster forcefully:

1. Identify the current vSAN leader by running command esxcli vsan cluster get on a host in the cluster and place it into maintenance mode.
2. Run the below command to abdicate the current vSAN leader:
   • For ESXi 6.7 U3 P04 to 7.0 U1 version, use the command: vsish -e set /vmkModules/cmmds/forceTransition abdicateMaster
   • For ESXi 7.0U2 and higher versions, use the command: vsish -e set /vmkModules/cmmds/forceTransition abdicateLeader
3. Running the command esxcli vsan cluster get on the host reveals that a new host is the vSAN leader.

Note: This will make the backup node to take over and agent nodes will failover to backup/newLeader without transitioning to the discovery state, and the cluster should not fall apart. The previous master node will still transition to discovery state (because master to agent is not a valid state transition), this is why it should be in maintenance mode to avoid any disruption to any running VMs.