ESX Disconnected after Upgrading to VirtualCenter 2.0.1

ESX Server 3.x Hosts Shown as Disconnected after Upgrading to VirtualCenter 2.0.1 Patch Releases

In some cases, after updating VirtualCenter to Patch 2 some or all of the ESX hosts are shown as disconnected. This happens because the VC agent (vpxa) update fails if /tmp/vmware-root is not present on the ESX host.

KnowlegeBase article 4478241 https://kb.vmware.com/kb/4478241 explains how to fix (or prevent) this issue.