VMware: The Summary tab of the ESXi/ESX host reports the warning - Unable to apply DRS resource settings on host

<< Error Message >>
The Summary tab of the ESXi/ESX host reports the warning:
1. Unable to apply DRS resource settings on host. A general system error occurred: vim.fault.InvalidState. This can significantly reduce the effectiveness of DRS.

or

2. Unable to apply DRS resource settings on host. There were too many consecutive overrides of the resource settings pushed from the cluster.. This can significantly reduce the effectiveness of DRS.


<< Solution >>
Restart the management agents on the ESXi/ESX host by following the steps below:
1. Log in to SSH or Local console as root.
2. Run these commands:
/etc/init.d/hostd restart
/etc/init.d/vpxa restart

Note: In ESXi 4.x, run this command to restart the vpxa agent:
service vmware-vpxa restart

Note: No downtime needed!


<< More Info >>
What is HOSTD?
The vmware-hostd management service is the main communication channel between ESX/ESXi hosts and VMkernel. If vmware-hostd fails, ESX/ESXi hosts disconnects from vCenter Server/VirtualCenter and cannot be managed, even if you try to connect to the ESX/ESXi host directly. It knows about all the VMs that are registered on that host, the luns/vmfs volumes visible by the host, what the VMs are doing, etc. Most all commands or operations come down from VC through it. i.e, powering on a VM, VM vMotion, VM creation, etc.

What is VPXA?
It acts as an intermediary between VC and hostd. The vCenter Server Agent, also referred to as vpxa or the vmware-vpxa service, is what allows a vCenter Server to connect to a ESX host. Specifically, vpxa is the communication conduit to the hostd, which in turn communicates to the ESX kernel.