> GHA with the `setup-ruby` action will cache gems.

Caching is a great word - it only means what we want it to mean. My experience with GHA default caches is that it’s absolutely dog slow.

> Buildkite can be used in tons of different ways, but it's common to use it with docker and build a docker image with a layer dedicated to the gems (e.g. COPY Gemfile Gemfile.lock; RUN bundle install), effectively caching dependencies.

The only way docker caching works is if you have a persistent host. That’s certainly not most setups. It can be done, but if you have that running in docker doesn’t gain you much at all you’d see the same caching speed up if you just ran it on the host machine directly.

This is what I came to say. We pre cache dependencies into an approved baseline image. And we cache approved and scanned dependencies locally with Nexus and Lifecycle.