Unable to configure HA agent on host, task fails with error "There was an error unconfiguring the vSphere HA agent on this host"

Products

• VMware vSphere ESXi

Issue/Introduction

• Configuring vSphere HA on the host fails with error "There was an error unconfiguring the vSphere HA agent on this host. To solve this problem, reconnect the host to vCenter Server."
  
  
  
  
• Logs on ESXi (/var/run/log/lifecycle.log) shows errors similar to below snippets while connecting to vCenter Server :
  
  "Temporary failure in name resolution"
  
  
  
  
• Issue is observed after patching ESXi 7.0.

Cause

• The ESXi host cannot resolve the DNS name of the vCenter server FQDN and due to that it was unable to contact vCenter Server to download the vSphere HA VIBs.
• DNS resolution of vCenter Server FQDN using 'nslookup' fails with error "connection timed out; no servers could be reached"
• Initiating a Ping to the default gateway IP Address of ESXi Management network and the Primary DNS Server IP fails on the same host. However, it can reach some other IPs such as secondary DNS Servers in a different subnet.

Resolution

Update the vSwitch Teaming policy if it is changed after ESXi patching, more details in KB vSwitch (Standard Switches) teaming Load balancing change to port id after ESXi 7.0.3l update.

Workaround.

• Ping all the DNS Servers configured on the host and change the order of DNS servers to keep the DNS Server IP Address which is pinging as the first address in /etc/resolv.conf.

Additional Information

Enabling HA on a cluster fails with error 'Applying HA VIBs on the cluster encountered a failure.'