How to upgrade a Rails app?

What is the procedure for re-launching a Rails app?
For example, I have upgraded Ruby version from 3.0.2 to 3.0.3 so, for starters the Dockerfile needs updating. What is the recommended way to do this? What else needs to be considered?

No need to re-launch. Edit the files and redeploy.

Check your Gemfile and see if you have a .ruby_version file. Also, if you have a Gemfile.lock file (and you probably do), run bundle update after you modify your Gemfile.

Thank you, Sam.
To confirm, as far as the fly.io specific files, the Dockerfile is the only one that needs changing?

I’m getting the following

Error failed to fetch an image or build from source: error building: 
failed to solve with frontend dockerfile.v0: failed to solve with 
frontend gateway.v0: rpc error: code = Unknown desc = 
quay.io/evl.ms/fullstaq-ruby:3.1.3-jemalloc-slim: not found

So I’m guessing there isn’t a Ruby 3.1.3 image available yet?
(I mistakenly referenced Ruby 3.0 in my original post)

Correct. Or rather, there isn’t one here: Quay

However you can find 3.1.3 here: Docker Hub - the difference is that those versions of Ruby aren’t compiled with jemalloc; which generally means that they will run slightly slower and more importantly use more RAM. I haven’t done the research yet, this post suggests that you can add jemalloc to an existing version of Ruby by installing one package and setting one environment variable: Add jemalloc to your Ruby Docker images, now! | storck.io

Great info.
Thank you very much.