Rails Postgre Docker MultiStage

Dockerfile

FROM ruby:2.5.5-alpine3.9 as builder

WORKDIR /app

ARG RAILS_MASTER_KEY

ENV BUNDLE_SILENCE_ROOT_WARNING=1 \
    BUNDLE_IGNORE_MESSAGES=1 \
    BUNDLE_GITHUB_HTTPS=1 \
    BUNDLE_FROZEN=1 \
    BUNDLE_WITHOUT=development:test 

RUN apk update && apk add --no-cache \
        build-base postgresql-dev libxml2-dev libxslt-dev nodejs tzdata git imagemagick

COPY Gemfile* ./
RUN gem install bundler && bundle install -j4 --retry 3

# Add the Rails app
COPY . /app        
RUN mv ./config/database.yml.sample ./config/database.yml && \
        bundle exec rake assets:precompile RAILS_ENV=production     

FROM ruby:2.5.5-alpine3.9

ARG RAILS_ENV=production

WORKDIR /app
COPY --from=builder /usr/local/bundle /usr/local/bundle
COPY --from=builder /app ./

RUN apk update && apk add --no-cache \
        postgresql-client tzdata nodejs imagemagick && \
        addgroup -g 1000 -S appuser && \
        adduser -u 1000 -S appuser -G appuser && \
        chown appuser:appuser /app -R 

EXPOSE 9292
USER appuser

CMD ["ruby", "init.rb"]

init.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

environment = ENV['RAILS_ENV']

container = ARGV[0] || 'api'

case container
when 'api'
  %w[db:create db:migrate].each do |rake_name|
    puts "-> rake #{rake_name}"
    exec "bundle exec rails #{rake_name}" unless system "bundle exec rails #{rake_name}"
  end

  if %w[stage production].include?(environment)
    puts '-> update whenever'
    exec 'bundle exec whenever --update-crontab && cron -f' unless system 'bundle exec whenever'
  end

  exec "bundle exec puma -e #{environment}"
when 'sidekiq'
  exec 'bundle exec sidekiq'
end