How HA Restarts a VM in case of host failure and If the host is unreachable which command is executed by HA to perform that? I just want to how it is happened?
A power on command.
It is not a single command that runs at the background to get HA working as effecient as it is now.
It does monitoring using the heartbeats and also refers to value in regards to the HA configuration. Based on the requirement it performs the suitable action, could be a restart or leave VMs as powered On.
To get a better insight read the article below :
http://www.vmware.com/products/datacenter-virtualization/vsphere/high-availability.html
Cheers,
NS