vCenter Server Appliance hangs or becomes unresponsive after DNS server removal

Products

• VMware vCenter Server

Issue/Introduction

• vCenter Server becomes "Not Responding" or the web client fails to load.
• The vCenter Appliance Management Interface (VAMI) on port 5480 is inaccessible.
• SSH sessions to the vCenter hang or time out during login using FQDN.
• ESXi hosts appear as "Disconnected" or "Not Responding" in the inventory.
• vCenter (VAMI,SSH) is accessible only with IP

 

Environment

VMware vCenter Server 8.0.x

Cause

When a DNS server is removed from the vCenter Server configuration, or when name resolution becomes unavailable, the vCenter Server Appliance (VCSA) may become completely unresponsive to the vSphere Client, VAMI, and SSH. This occurs because core vCenter services have a critical dependency on continuous name resolution for inter-service communication.


vCenter Server core services (specifically vpxd, vpxd-svcs, and vmdir) are heavily dependent on immediate DNS resolution. If a configured DNS server is removed or becomes unreachable, services attempt to resolve Fully Qualified Domain Names (FQDNs) for inter-service communication and database connectivity. These resolution attempts suffer from "catastrophic timeouts," causing the service threads to hang and rendering the appliance unresponsive.

Resolution

To restore vCenter functionality, name resolution must be stabilized. Follow these steps:

1.  Verify DNS Configuration
         Once the appliance is back online, log in to the VAMI (https://<vCenter-IP>:5480).
         Navigate to Networking > DNS
   
   
   
2. Ensure all listed DNS servers are reachable and correctly resolving the vCenter FQDN and all ESXi host FQDNs.
   
   
3. Clear Stale DNS Cache
   
   
4. If connectivity issues persist despite correct DNS settings, SSH into the vCenter using IP and run:
          
           systemctl restart dnsmasq
           systemctl restart systemd-resolved
          
   Confirm Service Status
   Verify that all services are running:
          
           service-control --status --all
   
   
5. If above steps are not resolving this behaviour then reboot vCenter via hard reset/restart of the VCSA VM from the ESXi host where it is residing

Additional Information

Clear DNS Cache on vCenter Server

Update DNS Server IP address for vCenter Server Appliance