Cannot put Esxi host into maintenance mode: system_error Messages: vapi.send.failed<Send of frame failed

Products

• VMware vCenter Server 8.0

Issue/Introduction

Try to put an Esxi host into maintenance mode,  the task goes to 2%, then failed with error:

   Failed to enter namespaces maintenance mode due to Error: system_error Messages: vapi.send.failed<Send of frame failed: N7Vmacore15SystemExceptionE(Connection refused: The remote service is not running, OR is overloaded, OR a firewall is rejecting connections.)

Environment

vCenter Server 7.0.x

vCenter Server 8.0.x

Cause

The wcp service on vCenter Server side is not running.

This issue is very similar with KB367329, but we cannot find anything about wcpsvc-vmonconfig.json in vmon.log,so this is not the same issue in  KB367329.  

Resolution

Ensure wcp service is up and running.  

For this case, we simply run 

    service-control --start --all

then wcp service is back to normal.

If there is anything wrong about wcp service, fix it first, then the Esxi host should be able to enter into maintenance mode.