If you’re using bundler for your ruby or rails project and docker you will run into docker having to install your gems everytime. You can either make a base image that has the bundle cache already on it, or you can make a small cache step in your Dockerfile.

Here I’ve setup a cache user and host to store the cache tar. It will attempt to download and untar it, run bundle, then attempt to tar and re-upload it.

1RUN scp -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no [email protected]:~/project.tar.gz . || true
2RUN tar xzf project.tar.gz || true
3RUN bundle install --deployment --without development test
4RUN tar czf project.tar.gz vendor
5RUN scp -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no project.tar.gz [email protected]:~/ || true

Doing this cut build times for my image from a few minutes to a few seconds. If you have any other tricks for speeding up builds, let me know!