I am running ESXi 5.0 and vCenter 5.0.
Shortly after correcting some issues I had today in my Virtual Switches and Virtual adapters everything seemed to be doing great until ... All of a sudden my vSphere Vcenter server went down. Problem is that my vCenter server is a VM itself.
I have no access to vCenter console. In ESX 4 you could use the Web Interface to connect to an individual host and manage the VM's from there. In ESX 5 you can't (at least that I know of)...
I need to connect to my vSphere and vCenter to scope out the issue. I now cannot ping the vCenter server.
This is critical because server of the servers that are on the same host are also unavailable.
To add to a.p. ... depending on the size of your environment and features used, you can setup DRS rules to ensure that you always know where your vCenter VM is located.
I have 30 hosts with ~650 VM's (using fully automated HA/DRS clusters) ... to save connecting to each host and looking for the VC server I have simply created a DRS rule to ensure that it is always located on the first host, in the first cluster, and on the first datastore ... if it ever goes down, I know exactly where to look from a host and storage perspective.
as a.p said you can use vSphere Client 5.0 to connect to the host directly and manage the vCenter Server VM.
To ensure hight availability for the vCenter server you can go for vCenter Server heartbeat. Refer the following link for more details.