I think the first time I ran /discourse-setup it installed Docker for me.
And after hacking together a manual entry in the/etc/hosts file of the container environment for github’s IP address, it now says “connection timed out” instead of “unable to resolve github.com”.
So it seems like it might be an internet connection problem in general and not just a DNS thing. I even tried running it with the --network host option and it still didn’t work even though it does work on my host.
If I run a simple test Docker container, I am able to reach the internet from it. It just seems like the Discourse container is not connecting out.