All ESXi hosts are disconnected or in not responding state after vCenter reboot

Products

• VMware vCenter Server

Issue/Introduction

All hosts in the vCenter inventory are showing in a "Disconnected" or "not responding" state in vCenter following vCenter reboot or DNS change.

Hosts are not (re-)connecting to vCenter when trying manually connect them.

vCenter cannot synchronize with any hosts in cluster.

The hosts are added within vCenter via FQDN.

Pings from the vCenter VM to any FQDN target fail, but the vCenter VM can ping the same targets' IP addresses without issue.

The vCenter itself may be reachable via IP and FQDN.

Environment

VMware vCenter (all versions)

Cause

The DNS server the vCenter appliance is leveraging is either not reachable or not functioning.

Resolution

The DNS cache on the vCenter can be cleared to try and remediate the issue. See Clear DNS Cache on vCenter Server for more information.

If the vCenter VM can reach the DNS target though, and all vCenter services are running normally, the issue may be with the DNS traffic or the DNS server itself failing to allow vCenter to resolve IPs normally. Therefore it is recommended to engage your network team or vendor to troubleshoot the DNS server and/or datapath between the vCenter and DNS.