Rails MariaDB Docker MultiStage

Dockerfile

FROM ruby:2.5.5-alpine3.9 as builder

WORKDIR /app

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 mariadb-dev nodejs tzdata

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

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

FROM ruby:2.5.5-alpine3.9

ENV 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 \
        mariadb-connector-c tzdata nodejs && \
        addgroup -g 1000 -S appuser && \
        adduser -u 1000 -S appuser -G appuser && \
        chown appuser:appuser /app -R 

EXPOSE 3000
USER appuser

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

init.rb

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

environment = ENV['RAILS_ENV']

exec "bundle exec rails db:migrate && bundle exec puma -e #{environment}"