We were having problems after upgrading Tomcat on our vCenter server; some of the plugins were not working (hardware and services health monitoring). Through research, I discovered that upgrading Tomcat on its own is not recommended, the preferred method being to upgrade vCenter server itself. Before upgrading Tomcat, we had taken a snapshot, so to address the plugin issue, we reverted to snapshot. Since doing so, we are no longer connect any of our esxi hosts. We can still manage the VMs (including the vCenter server) by using vSphere client to access the esxi hosts directly. All hosts can still ping vCenter server and the vCenter server can ping the hosts (both IP and host name), so the network is good and DNS is working. (I can't see the firewall settings because I can't access cluster settings due to vCenter server being disconnected from the hosts). All of the vCenter services appear to be running on the vCenter server, although some are set to manual and I am not sure which ones are absolutely required. I'm leaning in the direction of building a new vCenter server and connecting our hosts to that so we can restore HA and DRS, but I am wondering has any input on our original vCenter server problem. Thanks.