Second Identity server upgrade?

I have a question about upgrading an essentials site with a second identity server.  As described in this article: https://support.geocortex.com/install-multiple-identity-servers I have installed a second identity server and it is working great!  The question is on upgrading.  I do not believe the second identity server is being upgraded during the upgrade process.

The questions are:

1. Does it need to be upgraded?

2. If so, how do you upgrade it?