Fly + PlanetScale + Rails example dockerfile

If you are debugging this error:

  LoadError: libmariadb.so.3: cannot open shared object file: No such file or directory - /rails/vendor/bundle/ruby/2.7.0/gems/mysql2-0.5.5/lib/mysql2/mysql2.so

The fix is having these packages installed for production: default-mysql-client default-libmysqlclient-dev

Here's a full example Dockerfile

# syntax = docker/dockerfile:1

# Make sure RUBY_VERSION matches the Ruby version in .ruby-version and Gemfile
ARG RUBY_VERSION=2.7.2
FROM registry.docker.com/library/ruby:$RUBY_VERSION-slim as base

# Rails app lives here
WORKDIR /rails

# Set production environment
ENV RAILS_ENV="production" \
    BUNDLE_WITHOUT="development:test" \
    BUNDLE_DEPLOYMENT="1"

# Update gems and bundler
RUN gem update --system --no-document && \
    gem install -N bundler


# Throw-away build stage to reduce size of final image
FROM base as build

# Install packages needed to build gems and node modules
RUN apt-get update -qq && \
    apt-get install --no-install-recommends -y build-essential curl libmariadb-dev default-libmysqlclient-dev libvips node-gyp pkg-config python

# Install JavaScript dependencies
ARG NODE_VERSION=16.16.0
ARG YARN_VERSION=1.22.19
ENV PATH=/usr/local/node/bin:$PATH
RUN curl -sL https://github.com/nodenv/node-build/archive/master.tar.gz | tar xz -C /tmp/ && \
    /tmp/node-build-master/bin/node-build "${NODE_VERSION}" /usr/local/node && \
    npm install -g yarn@$YARN_VERSION && \
    rm -rf /tmp/node-build-master

# Install application gems
COPY --link Gemfile Gemfile.lock ./
RUN bundle install && \
    bundle exec bootsnap precompile --gemfile && \
    rm -rf ~/.bundle/ $BUNDLE_PATH/ruby/*/cache $BUNDLE_PATH/ruby/*/bundler/gems/*/.git

# Install node modules
COPY --link package.json yarn.lock ./
RUN yarn install --frozen-lockfile

# Copy application code
COPY --link . .

# Precompile bootsnap code for faster boot times
RUN bundle exec bootsnap precompile app/ lib/

# Precompiling assets for production without requiring secret RAILS_MASTER_KEY
RUN SECRET_KEY_BASE=DUMMY ./bin/rails assets:precompile


# Final stage for app image
FROM base

# Install packages needed for deployment
RUN apt-get update -qq && \
    apt-get install --no-install-recommends -y curl default-mysql-client default-libmysqlclient-dev imagemagick libvips && \
    rm -rf /var/lib/apt/lists /var/cache/apt/archives

# Copy built artifacts: gems, application
COPY --from=build /usr/local/bundle /usr/local/bundle
COPY --from=build /rails /rails

# Run and own only the runtime files as a non-root user for security
ARG UID=1000 \
    GID=1000
RUN groupadd -f -g $GID rails && \
    useradd -u $UID -g $GID rails --create-home --shell /bin/bash && \
    chown -R rails:rails db log tmp
USER rails:rails

# Deployment options
ENV RAILS_LOG_TO_STDOUT="1" \
    RAILS_SERVE_STATIC_FILES="true"

# Start the server by default, this can be overwritten at runtime
EXPOSE 3000
CMD ["./bin/rails", "server"]