Ready to use Rails 5.2 + Ruby 2.6

Dockerfile

# Usage: `docker build --build-arg RAILS_MASTER_KEY=$RAILS_MASTER_KEY -t myapp .
FROM ruby:2.6.2-slim

ARG RAILS_MASTER_KEY

# Install NodeJS
RUN apt-get update \
  && apt-get install -y apt-transport-https curl gnupg2 \
  && curl --silent --show-error --location https://deb.nodesource.com/gpgkey/nodesource.gpg.key | apt-key add - \
  && echo "deb https://deb.nodesource.com/node_6.x/ stretch main" > /etc/apt/sources.list.d/nodesource.list \
  && apt-get update \
  && apt-get install -y nodejs \
  && apt-get clean \
  && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*

# Install Yarn
RUN curl --silent --show-error --location https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - \
  && echo "deb https://dl.yarnpkg.com/debian/ stable main" > /etc/apt/sources.list.d/yarn.list \
  && apt-get update \
  && apt-get install -y yarn \
  && apt-get clean \
  && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*

# Install essentials for Bundle Install
RUN apt-get update \
  && apt-get install -y libxslt-dev libxml2-dev zlib1g-dev build-essential

# Install PostgreSQL support
RUN apt-get update \
  && apt-get install -y libpq-dev

WORKDIR /app

ENV RAILS_ENV=production
ENV NODE_ENV=production

COPY Gemfile Gemfile.lock /app/
RUN gem install bundler && bundle install --jobs 4 --without development:test --deployment

COPY . /app/

RUN RAILS_MASTER_KEY=$RAILS_MASTER_KEY bin/rails assets:precompile

CMD ["/app/bin/rails", "server", "-b", "0.0.0.0", "--port", "3000"]