vCenter UI is inaccessible and fails with "Service did not set the task state" when updating DNS servers in VCF 9.x

Products

• VMware vCenter Server

Issue/Introduction

 

• The vCenter Server Appliance (VCSA) Web UI or VAMI interface (https://<vcenter-fqdn>:5480) becomes completely inaccessible or intermittent.

• Attempting to modify or update the DNS server configurations using the VAMI Network Settings Wizard fails at the "Ready to Complete" stage with the error:

  Service did not set the task state

• Core services (such as applmgmt, vsphere-ui, or vpxd) show as Running via service-control --status, but local lookups using nslookup return communication timeouts:communications error to 127.0.0.1#53: timed out

• After manually modifying /etc/resolv.conf, the new settings revert back to the original IP addresses upon a system reboot.

 

Environment

VMware vCenter Server 9.0

Cause

This issue occurs due to a known validation loop within the appliance management framework (applmgmt).

When modifying DNS settings via the VAMI UI, the backend configuration engine attempts to validate network layer connectivity and execute forward/reverse name resolution queries through the local loopback resolver (127.0.0.1 via systemd-resolved). If the local resolver encounters a timeout or is caught transitioning between old and new DNS records, the UI-driven task pipeline hangs.

Because the pipeline stalls, the task engine times out internally before committing the changes to the master networking configuration database (/etc/issue, netconfig). Consequently, the operating system falls back to its old cached profiles upon the next network reload or reboot.

Resolution

To bypass the UI validation bug and permanently apply the required configurations, we executed the following steps via the command-line interface (CLI):

Changing the DNS servers using DCLI:

1. Open a console to the VCSA and log in as the root user.
2. If the appliance shell is the active default shell, proceed to step 4; otherwise, proceed to step 3.
3. If the BASH shell is the active default shell, access the appliance shell by entering: appliancesh
4. Run the following command to retrieve the current DNS configuration:
   
   dcli com vmware appliance networking dns servers get

(Note: The [e-mail] credentials are required when the command prompts for a username and password.)
   
   
5. Run the following command to set the DNS servers:
   
   dcli com vmware appliance networking dns servers set --mode is_static --servers ##.##.##.## --servers ##.##.##.##

(Note: To add multiple entries, the --servers flag must be appended multiple times. Rerunning the command overwrites existing values.)