On Tue, Nov 7, 2017 at 3:19 PM, glarkin53 <greg.larkin@puppet.com> wrote:

I'm working on a project to provide access to Windows desktops hosted on
Amazon AWS. We spin up a number of Windows EC2 instances (Windows 2012 R2
servers) and then connect to them with Guacamole.

Upon the first connection to a machine, it has the Amazon auto-generated
hostname, such as "win-oekuqjop15l.us-west-2.compute.internal". Our process
requires the hostname to be changed and the machine rebooted, so we may
issue the following commands in a Powershell window:

Rename-Computer glarkin

After the machine restarts, Guacamole is unable to connect to the machine.
The dialog box reads "The remote desktop server is currently unreachable."
The machine is still up and running, and I can connect to it with a desktop
RDP client from my laptop, so I think there is a problem with Guacamole

I suspect that you're running into a DNS caching issue on the system hosting Guacamole.  Depending on what distribution you're running, there could be one of several daemons running that caches DNS information.  sssd, nscd, and nslcd are the ones I can think of off the top of my head.  Also, depending on which DNS servers you're pointing at with your laptop vs. Guacamole, it could be something on one of those systems, too.