Optimized dockerfile for Rails

Dockerfile

# Main stage responsible for installing and configuring Rails and assets dependencies
FROM ruby:3.0.4-alpine AS ruby-base

ARG RAILS_MASTER_KEY
ARG BUNDLER_VERSION=2.3.12

ENV RAILS_MASTER_KEY=${RAILS_MASTER_KEY}
ENV RAILS_ENV=production
ENV NODE_ENV=production

# Install system packages required by gems (timezone update may be skipped here)
RUN apk update && apk add \
    build-base \
    postgresql-dev \
    nodejs \
    npm \
    tzdata \
    gcompat \
    && cp /usr/share/zoneinfo/America/Toronto /etc/localtime \
    && rm -rf /var/cache/apk/*

RUN gem install bundler -v ${BUNDLER_VERSION} \
    && npm install -g yarn

# See https://bundler.io/v2.3/guides/bundler_docker_guide.html
ENV GEM_HOME="/app/vendor/bundle/ruby/3.0.0"
ENV PATH=$GEM_HOME/bin:$GEM_HOME/gems/bin:$PATH

WORKDIR /app

COPY Gemfile Gemfile.lock yarn.lock ./

# Configure bundler to install dependencies without dev and test to app/vendor
RUN bundle config set --local deployment true \
    && bundle config set --local without development test \
    && bundle install --jobs 4

COPY . .

# Update binstubs so that app/bin references the correct gems under app/vendor + precompile webpacker assets
RUN yarn install --check-files --production \
    && rake app:update:bin \
    && rails webpacker:binstubs \
    && RAILS_MASTER_KEY=${RAILS_MASTER_KEY} bundle exec rails assets:precompile \
    && rm -rf node_modules tmp/cache vendor/assets

# Second and final build stage
FROM ruby:3.0.4-alpine

ARG USERNAME=concierge
ARG USER_UID=1000
ARG USER_GID=$USER_UID
ARG BUNDLER_VERSION=2.3.12

# Install system packages required by some gems to be able to run, updates timezone and add a custom user to run the container
RUN apk update && apk add \
    nodejs \
    libpq \
    tzdata \
    gcompat \
    && cp /usr/share/zoneinfo/America/Toronto /etc/localtime \
    && rm -rf /var/cache/apk/* \
    && addgroup -g ${USER_GID} ${USERNAME} \
    && adduser -D ${USERNAME} -u ${USER_UID} -G ${USERNAME}

ENV RAILS_ENV=production
ENV GEM_HOME="/app/vendor/bundle/ruby/3.0.0"
ENV PATH=$GEM_HOME/bin:$GEM_HOME/gems/bin:$PATH

WORKDIR /app

# Copy /app with dependencies already installed and assets compiled, ownership set to our custom user
COPY --from=ruby-base --chown=${USERNAME}:${USERNAME} /app ./

# Sets additional bundler configuration so it knows where/what to read from + updates binstubs
RUN gem install bundler -v ${BUNDLER_VERSION} \
    && bundle config --local path vendor/bundle \
    && bundle config --local without development test \
    && rake app:update:bin

# instructs docker to run the container as the user created a few lines above
USER ${USERNAME}

LABEL maintainer="Rodrigo Z.A."