re: Demystifying Docker Compose VIEW POST

re: I hope this doesn't sound stupid but why didn't we just do COPY . /my-api RUN bundle install instead of the longer version COPY Gemfile /my...

Each line is cached, so if I only use COPY . /my-api I will have to run bundler every time anything in my code changes, which takes time and would be annoying.

By copying over the gemfiles first and running bundler those packages are cached and rebuilds will be faster. As docker-compose is smart enough to realize those files didn't change so it will skip the gemfile and bundler steps when building.


Ahh. That makes sense. Thanks for clearing things up for me 😁


You could instead use a volume in docker-compose

It wouldn't change the need to rebuild and rerun bundler if the gemfiles changed. I always prefer to rebuild the container when updating gemfiles. I don't want my docker-compose file to get out of sync with what happens in my container.

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