PSC not switching on secondary DNS

Once primary DNS server down , PSC lost the communication on secondary DNS.

Scenario:- 2 PSC appliances, 2 DNS server (appliances) with NLB

error:- The v Sphere Client could not connect to vCenter FQDN or IP Address. The server vCenter FQDN or IP Address took too long to respond. (The command has timed out as the remote server is taking too long to respond.

Cause:- This issue occurs if the primary DNS server is unavailable. Due to this, the default timeout & retry values used by vCenter Server Appliance to switch the secondary DNS server cause an excessive delay.

Resolution:-

To reduce the timeout value and allow the appliance to fail over to the next available DNS server, modify the /etc/resolv.conf file.

Note: If you are using a dispersed vSphere topology with one or more external PSCs, vCenter Management nodes, and Single Single On node, you must perform these steps on all appliances. If you modify the DNS settings through the VAMI or the virtual machine console, these values are lost and need to be reapplied.

Note: Take a snapshot of vCenter Appliance before proceeding.

1. Take an SSH session to vCenter Server Appliance.
2. Take a backup of the /etc/resolv.conf file.
3. Open the /etc/resolv.conf file using a suitable text editor.
4. Add these values to the end of the file:
   
   options timeout:1 attempts:1 rotate
   
   Notes:
   • The timeout value controls the time in seconds before moving on to the next DNS server.
   • The attempts value controls the number of retries before moving to the next DNS server.
   • The rotate value adds a round robin behavior.
5. Save and close the file.
6. Reboot the appliance.