David Kimura PRO said 4 months ago on Docker on Rails 7 :
  You are correct! Having the bundle volume doesn't map to your development machine's bundle directory. Honestly, I don't think I would want to do this anyways since there are some gems that compile native extensions. Since I develop on a macOS machine, doing this could introduce unexpected errors from the compiled gems. Having the bundle volume is still useful though if you have multiple services that rely on the application code (sidekiq, jsbundling, and cssbundling). So, when you run bundle in the app docker container, the installed gems would be available to the other services.