I have a client that is indicating that the VMs are disconnected in their vCenter, that was the day of yesterday, today I connect to check the vCenter, and observed that there are no objects in the inventory of the vCenter. Host, VM, Datastores or switches are not displayed, even I am entering with the user administrators.
However, at the vCenter services level everything is Ok. I think you should add the hosts again the inventory.
In the same way I listen to your suggestions.
If VMs are labeled as "disconnected" it's because vCenter lost connection with hosts. Check if You can add any host to vCenter inventory.
I am trying to connect the host to the vcenter and it tells me the following error.
I already restart the administration agents with the following commands and it does not allow me to add it to the vcenter.
Check IP address of vCenter and hosts management interface. Check if You can ping on FQDN and IP address of this host from vCenter.
If the host is not identified by FQDN then name service is not working or is not configured on vCenter. If the host is not answering for ping using IP address, then resolve network connectivity problem.
If You can ping host's management interface from vCenter's shell using FQDN or IP address You don't need to remove host from inventory and readd once again. This will not prove anything. Check if host sees remote storage device if any exists in your environment. If hosts can access remote datastores check why heartbeats are not arriving from host to vCenter in 60 seconds window.
Is this vCenter local or remote from your hosts?
If host is not yet added to vCenter, You can add it even if the VMs are running.
Did their networking team do any changes, or was any maintenance done? The screenshot shows vcenter can't talk to the hosts over the management network, like was said before see if you can get on the vCenter host and see if you can ping on of the hosts. If you can get to the esxi web interface the host is up, and the vms are fine if you can see them running there. Removing the host and readding them shouldn't restart the vms, but can cause the vms not to go back into the right host or I think the may lose tags that have been assigned.
Please do what sjesse said, and try to connect to the ESXi host's web GUI. If the host's IP address is reachable/pingable, but you cannot access the web GUI, then there may either be an issue with the host's services, or there's another system with the same IP address on the network.
You could do a services.sh restart which restarts most of the components from the ESXi host. This should also not affect the virtual machines that are in production.