Docker Cache BUNDLE INSTALL not working

Each time you change any file in your local app directory, the cache will be wiped out, forcing every step afterwards to be re-run, including the last bundle install.

The solution is don't run bundle install in step 2. You have already installed your gems in step 1 and there is little chance the Gemfile will change between step 1 and step 2 ;-).

The whole point of step 1 is to add your Gemfile, which should not change to often, so you can cache it and the subsequent bundle command before adding the rest of your app, which will probably change very often if you are still developing it.

Here's how the Dockerfile could look like:

1. WORKDIR /tmp ADD ./Gemfile GemfileADD ./Gemfile.lock Gemfile.lockRUN bundle install2.ADD . opt/railsapp/WORKIDR opt/rails/app

Versions of Docker before 0.9.1 did not cache ADD instructions. Can you check that you're running a version of Docker 0.9.1 or greater?

Also, which installation of Docker are you using? According to this GitHub issue, some users have experienced cache-busting ADD behavior when using unsupported Docker builds. Make sure you're using an official Docker build.

ADD caching is based on all the metadata of the file, not just the contents.

if you are running docker build in a CI-like environment with a fresh checkout, then it is possible the timestamps of the files are being updated which would invalidate the cache.