@jeverling I'm curious as to how this happened. Even if AWS was reusing internal IP addresses, and EC2 host names are based on it's private IP address, it can only cause two different EC2 hosts at different points in time to have the same host name. If that is the case, what's the problem here? Does GitHub expect new names every time a runner registers to GitHub and not reuse any old names used by old runners that don't exist anymore?

Does GitHub expect new names every time a runner registers to GitHub and not reuse any old names used by old runners that don't exist anymore?

Exactly, Github keeps a registry of runners, and refuses registering a runner with a name that has been used before. It might be possible to deregister runners or solve this in other ways, but I think using unique names for runners isn't a bad solution to this problem.

yeah, deregistering is a good way to solve the problem

Unique name is good in general 👍 I'm gonna use your solution for unique name