Cannot synchronize host "Hostname". There was an error unconfiguring the vSphere HA agent on this host. To solve this problem, reconnect the host to vCenter Server. vSphere HA agent on this host is disabled

Products

• VMware vSphere ESXi
• VMware vCenter Server

Issue/Introduction

• ESXi host fails to update information to vCenter Server
• ESXi host shows a disconnected status in the vCenter Server vSphere Client UI
• On the Summary page of the host, the following errors may appear:

VMware esx cannot synchronize host "incorrect username and password"

Cannot synchronize host : Cannot complete login due to an incorrect user name or password

Quick stats on "Hostname" is not up-to-date

• In an SSH to vCenter Server, attempting to run the following Networking commands to test connectivity to the ESXi host from vCenter Server fail even though pings are successful

nslookup <HostFQDN and IP>


openssl s_client -connect <HostFQDN or IP>:443

Environment

vSphere 7.x, 8.x

Cause

This is caused due to probable issue with the DNS forward/reverse lookup records for the ESXi host.  Both ESXi and vCenter Server require valid, forward and reverse DNS (Domain Name System) records for proper operation, with vCenter specifically needing a Fully Qualified Domain Name (FQDN) during installation. ESXi hosts must have their DNS settings configured, while the vCenter Server Appliance (VCSA) needs both forward and reverse lookup resolution of FQDN and ip for itself and the ESXi hosts.

Resolution

Review and fix the DNS connectivity and ensure the Forward and Reverse DNS records are addressed and confirmed in place for both vCenter Server and the ESXi hosts. Once communication between the host and vCenter Server is working correctly, the not responding hosts will reconnect to vCenter Server, the disconnected hosts need to be manually connected back

Workaround:

Follow these steps to add the host's information to the /etc/hosts file on the vCenter Server.

• SSH to the vCenter Server appliance
• Open the /etc/hosts file using editor:

vi /etc/hosts

• Goto insert mode by pressing I button
• Add the host details that is/are not connecting to vCenter Server in the format: ip fqdn shortname

For example:

192.168.#.# esx-server-1.example.com esx-server-1

• Press ESc and save the file using below command:

:wq!

Additional Information

Identifying issues with and setting up DNS name resolution on ESXi Server