As I migrate all of my Rails apps to Docker, I've learned to avoid making changes to the Gemfile whenever possible.
Whilst there are workarounds that can help to speed things up, any change to your
Gemfile results in a lengthy (re)download and install of all the gems in your app.
Sometimes I only needed to generate a new
Gemfile.lock so that the image could be built, tested and published by our continuous deployment server. Frustratingly, this meant having to wait for the redundant local
bundle install to complete before I could commit the new lock file.
Today, I discovered a way to save the hours wasted downloading gems: bundler's lock command.
This gem1 of a command resolves your app's dependencies and writes out the appropriate
Gemfile.lock – without installing any of the gems themselves.
Using Bundle Lock with Docker
Use the following command in your app's path to quickly create your
# cd /path/to/my-rails-app $ docker run --rm -v $(pwd):/usr/src/app -w /usr/src/app ruby:2.3.1 bundle lock
If you have an existing lock file, but want to update the gems (equivalent to
bundle update), just add the
# cd /path/to/my-rails-app $ docker run --rm -v $(pwd):/usr/src/app -w /usr/src/app ruby:2.3.1 bundle lock --update
Hopefully this will save you some time (and bandwidth) when building your Rails apps on Docker.
Pun very much intended ↩