While rebuilding my lab from scratch with

  • vSphere 7.0 U3c
  • NSX Advanced (AVI) Load Balancer 21.1.3

I hit a situation where my TKGS installation would not continue with an error, it was stuck for hours:

The control plane VM <ID> was unable to authenticate to the load balancer (Avi - https://<NSX ALB Controler IP>:443/api/cluster) with the username '<user>' and the supplied password. Validate the Supervisor cluster load balancer's authentication configuration.

To make a long story short, while user, password and connectivity check out it looks like the AVI defaults changed along the way. Make sure you enable “Allow Basic Authentication” in the Controller settings (Administration –> Access Settings) of the load balancer

Image Caption
NSX ADV Load Balancer settings

WCP will retry and eventually resolve the error once you change the setting on the load balancer.