dockhand

dockhand is a collection of helper commands that you can run inside a Docker container to set up a Rails application.

$ dockhand --help
Commands:
  dockhand help [COMMAND]                     # Describe available commands or one specific command.
  dockhand install-gems                       # Install gems with Bundler.
  dockhand install-node                       # Install Node.js.
  dockhand install-node-modules               # Install Node.js modules using Yarn, NPM, or PNPM.
  dockhand install-packages [PACKAGES...]     # Install apt packages.
  dockhand prepare-rails-app                  # Precompile assets, precompile code with Bootsnap, and normalize binstubs.
  dockhand rails-entrypoint                   # Entrypoint for a Rails application.
  dockhand transmute-to-artifacts [PATHS...]  # Move files and directories to an artifacts directory, and replace the originals with symlinks.

For example, in the following Dockerfile:

FROM ruby:3.2.0-slim

RUN gem install dockhand

WORKDIR /rails

COPY Gemfile Gemfile.lock .
RUN dockhand install-packages --buildtime --gem-buildtime --gem-runtime --clean \
 && dockhand install-gems --clean

COPY . .
RUN dockhand prepare-rails-app --clean

ENV RAILS_ENV=production
ENTRYPOINT ["dockhand", "rails-entrypoint"]
CMD ["bin/rails", "server"]
EXPOSE 3000

dockhand install-packages ... installs the apt packages needed for common gems in the Gemfile, such as libsqlite3-0 if using the sqlite3 gem or postgresql-client if using the pg gem. Then it cleans up the apt cache directories so the image won't contain unnecessary files.
dockhand install-gems ... installs the gems specified by Gemfile.lock, treating the lock file as frozen to ensure reproducible builds. Then it cleans up Bundler's cache so the image won't contain unnecessary files.
dockhand prepare-rails-app ... precompiles code with bootsnap, precompiles assets with a dummy SECRET_KEY_BASE, and fixes binstubs in bin/ for Windows users. Then it cleans up the assets precompilation cache so the image won't contain unnecessary files.
dockhand rails-entrypoint injects a call to bin/rails db:prepare if the given command is bin/rails server (or an alias thereof).

As another example, the following Dockerfile uses a multi-stage build and precompiles assets using Node.js:

# Builder stage
FROM ruby:3.2.0-slim as builder

RUN gem install dockhand

WORKDIR /artifacts/rails

COPY Gemfile Gemfile.lock .
RUN dockhand install-packages --buildtime --gem-buildtime \
 && dockhand install-gems --clean \
 && dockhand transmute-to-artifacts $GEM_HOME

COPY .node-version package.json yarn.lock .
RUN dockhand install-node \
 && dockhand install-node-modules

COPY . .
RUN dockhand prepare-rails-app --clean


# Application stage
FROM ruby:3.2.0-slim

RUN gem install dockhand

WORKDIR /rails

COPY Gemfile Gemfile.lock .
RUN dockhand install-packages --gem-runtime --clean

COPY --from=builder /artifacts /

ENV RAILS_ENV=production
ENTRYPOINT ["dockhand", "rails-entrypoint"]
CMD ["bin/rails", "server"]
EXPOSE 3000

dockhand transmute-to-artifacts ... moves /usr/local/bundle ($GEM_HOME) to /artifacts/usr/local/bundle and creates a symlink at /usr/local/bundle that points to /artifacts/usr/local/bundle. This makes it easy to copy gems as artifacts from the builder stage to the final application stage, while still allowing subsequent commands in the builder stage to use those gems.
dockhand install-node installs the appropriate version of Node.js based on .node-version. If you don't provide a .node-version file, it will try to choose a version based on the engines.node value in package.json.
dockhand install-node-modules installs Node.js modules specified by yarn.lock, using the appropriate version of Yarn and treating the lock file as frozen to ensure reproducible builds. It also supports NPM and PNPM lock files.

If you're looking for a more turn-key solution for your application's Dockerfile, including reduced build times using mounted caches, check out railbarge which is built on dockhand.