All ESXi not responding or disconnecting & reconnecting to their managed vCenter Server

Products

• VMware vCenter Server

Issue/Introduction

Multiple esxi hosts are going into a non responding state in the vCenter web interface. 

Environment

vCenter Server 7

Cause

vCenter is attempting to reach all of the hosts in vCenter using their FQDN but the DNS server is unable to resolve 1 or more host name leading to API calls that queue up for processing host heartbeats

 

Using the below search will identify the hosts vCenter is stuck attempting to resolve the DNS for. 

cat vpxd.log | grep "Failed to resolve address" | grep "HostSync" | grep -i "Host not found"

 

2025-11-05T01:05:35.883Z warning vpxd[07437] [Originator@6876 sub=IO.Connection opID=HostSync-host-####-a02963a] Failed to resolve address; <resolver p:0x00007f8d0c07bc60, 'ESXI-FQDN:443', next:(null)>, e: 2(Host not found (non-authoritative), try again later), async: true, duration: 151515msec

 

Resolution

1. Ensure the DNS server used by vCenter are able to resolve the FQDN of every single host in vCenter. 

2. Create a manual entry in /etc/hosts file for the esxi hosts which can't be resolved by the DNS server.