NSX-T 2.1 was released right before the holiday break and one of the biggest enhancement is support for VMware's upcoming Pivotal Container Service (PKS) which you can read more about here. Right before I took some much needed time off with the family, I had attempted an upgrade of my existing NSX-T 2.0 environment and ran into an issue which turned out to be a known issue but apparently it is no where listed on the NSX-T 2.1 release notes.
I figure I would share the simple workaround as it drove me a bit insane trying to figure out what was going on. After successfully uploading the NSX-T 2.1 upgrade bundle and then starting the upgrade, which starts off by updating the Upgrade Coordinator component and shortly after, I am shown the following error message:
This page is only available on the NSX Manager where Upgrade Coordinator is running. To enable the service, run the command "set service install-upgrade enabled" on the NSX Manager. If the install-upgrade service is already enabled, try disabling it using "clear service install-upgrade enabled" and then enable it again.
Although the error seems to suggest the Upgrade Coordinator service may not be running (it was), even after performing the recommended operations, the error message continue to persists as seen in the screenshot below.
After reaching out to Engineering as I was out of ideas on how to further troubleshoot the issue, it turns out this was actually a known upgrade issue going from 2.0 to 2.1. Instead of connecting to the NSX-T Manager using its Hostname (FQDN), I needed to use the IP Address instead for the upgrade. Once I logged back in using the IP Address, I was no longer seeing the error message and could proceed with my NSX-T upgrade as shown in the screenshot below.