Example of Ruby on Rails 6 Multi-stage builds with Docker. Development/production environments share the same Dockerfile.

.Dockerfile

FROM ruby:2.7.1-slim AS base

LABEL maintainer="Yann Defretin <yann@defret.in"

# Common dependencies
RUN apt-get update -qq \
  && DEBIAN_FRONTEND=noninteractive apt-get install -yq \
    --no-install-recommends \
    build-essential=12.6 \
    gnupg2=2.2.12-1+deb10u1 \
    curl=7.64.0-4+deb10u1 \
    less=487-0.1+b1 \
    git=1:2.20.1-2+deb10u3 \
    vim=2:8.1.0875-5 \
    ssh=1:7.9p1-10+deb10u2 \
  && apt-get clean \
  && rm -rf /var/cache/apt/archives/* \
  && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* \
  && truncate -s 0 /var/log/*log

# Add PostgreSQL to sources list
SHELL ["/bin/bash", "-o", "pipefail", "-c"]
RUN curl -sSL https://www.postgresql.org/media/keys/ACCC4CF8.asc | apt-key add - \
  && echo 'deb http://apt.postgresql.org/pub/repos/apt/ buster-pgdg main' 11 > /etc/apt/sources.list.d/pgdg.list

# Add NodeJS to sources list
SHELL ["/bin/bash", "-o", "pipefail", "-c"]
RUN curl -sL https://deb.nodesource.com/setup_12.x | bash -

# Add Yarn to the sources list
SHELL ["/bin/bash", "-o", "pipefail", "-c"]
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - \
  && echo 'deb http://dl.yarnpkg.com/debian/ stable main' > /etc/apt/sources.list.d/yarn.list

RUN apt-get update -qq && \
  DEBIAN_FRONTEND=noninteractive apt-get install -yq \
    --no-install-recommends \
    libpq-dev=12.3-1.pgdg100+1 \
    postgresql-client-11=11.7-0+deb10u1 \
    nodejs=12.16.3-1nodesource1 \
    yarn=1.22.4-1 \
    cron=3.0pl1-134+deb10u1 && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* && \
    truncate -s 0 /var/log/*log

# Configure bundler
ENV LANG=C.UTF-8 \
  BUNDLE_JOBS=4 \
  BUNDLE_RETRY=3

RUN mkdir -p /mc-crm

COPY Gemfile* /mc-crm/

WORKDIR /mc-crm

RUN bundle install --jobs=10
RUN yarn install --check-files && yarn cache clean

# development stage
FROM base AS development

ENV RAILS_ENV development

COPY . /mc-crm

CMD ["bin/dev-start"]

# production stage
FROM base AS production

COPY . /mc-crm

ENV RAILS_ENV production
ENV NODE_ENV production


SHELL ["/bin/bash", "-c"]
RUN ["bundle", "exec", "rake", "assets:precompile"]

CMD ["bin/prod-start"]

dev-start.sh

#!/bin/bash

# stop on errors
set -e

# setup cronjobs
bundle exec whenever --update-crontab

# start cron service
service cron restart

# Remove a potentially pre-existing server.pid for Rails.
rm -f tmp/pids/server.pid

# setup database if it doesn't exist, otherwise run migrations if any
bundle exec rake db:prepare

# start webpack dev server
./bin/webpack-dev-server &

# start server
bundle exec rails server -b 0.0.0.0

prod-start.sh

#!/bin/bash

# stop on errors
set -e

# setup cronjobs
bundle exec whenever --update-crontab

# start cron service
service cron restart

# Remove a potentially pre-existing server.pid for Rails.
rm -f tmp/pids/server.pid

# setup database if it doesn't exist, otherwise run migrations if any
bundle exec rake db:prepare

# start server
bundle exec puma -C config/puma.rb

BUNDLE_JOBS=4 env var on line 49 and the --jobs=10 bundle install flag on line 58 seem to be at odds with each other.