Can't get Ruby to update so ./launcher rebuild app keeps failing

[RBoy]

Yes you can. Edit app.yml on a fresh install before building discourse (since you can’t downgrade). Pick the tag from GitHub. I had to do this some time ago when I had to restore to an old version before upgrading to the latest.

How would I install a certain (old) version of Discourse

Checkout the same version of discourse_docker that you use on your other server, maybe copy your app.yml from the old server and make the necessary changes. Also in app.yml, change the version from tests-passed to either a tag (e.g. v2.5.0.beta7) or use a git commit hash.

Now I make an image of the working version before I upgrade just case something went wrong.