A set of files that could serve as a starting point for a Docker-based Ruby on Rails application.

docker-compose.yml

services:
  app:
    # Assumes this image is available on Docker Hub. If it's not, you'd want to add this
    # config:
    #
    #   build:
    #     context: .
    #
    # @see https://docs.docker.com/compose/compose-file/#build
    image: jgarber623/thing-app
    # Instructs `docker compose up` to pull the latest version of the image defined above.
    # May or may not be desirable, depending on the circumstance. Could also be achieved
    # by running:
    #
    #   bin/start --pull always
    #
    # @see https://docs.docker.com/compose/compose-file/#pull_policy
    pull_policy: always
    container_name: thing-app
    # Initialize these services before the `app` service. Shutdown occurs in reverse
    # order. The degree to which this is necessary depends on the app's requirements,
    # of course.
    depends_on:
      - db
      - redis
    # Equivalent to passing the `--init` flag to `docker run`. Dramatically speeds up
    # container shutdown.
    #
    # @see https://docs.docker.com/compose/compose-file/#init
    init: true
    # Adding an entrypoint script so we can output helpful information to the user
    # when invoking `bin/start`.
    entrypoint: ./docker-entrypoint.sh
    ports:
      - "3000:3000"
    volumes:
      - type: bind
        source: .
        target: /usr/src/app
        consistency: delegated
      - type: volume
        target: /usr/src/dependencies
  db:
    image: postgres:14-alpine
    container_name: thing-db
    environment:
      POSTGRES_PASSWORD: postgres
  redis:
    image: redis:7-alpine
    container_name: thing-redis

# Docker automatically defines and names networks somewhat randomly, so we instead
# specify a name for the network used by the services above. If you ever need to
# access details about the network, you'll know its name.
networks:
  default:
    name: thing-network

docker-entrypoint.sh

#!/usr/bin/env sh

set -e

# Output some helpful messaging when invoking `bin/start` (which itself is
# a convenience script for `docker compose up`.
#
# Adding this to work around the mild inconvenience of the `app` container's
# entrypoint generating no output.
#
cat <<-'PROMPT'

🤖 thing-app container initialized!

To continue, run the following command in a new Terminal tab:

  bin/exec bin/run

Use `ctrl-c` to exit.

PROMPT

# Using `sleep infinity` instead of `tail -f /dev/null`. This may be a 
# performance improvement based on the conversation on a semi-related
# StackOverflow page.
#
# @see https://stackoverflow.com/a/41655546
sleep infinity

Dockerfile

FROM debian:bullseye-slim

ARG NODE_VERSION="18.x"
ARG POSTGRESQL_VERSION="14"
ARG RAILS_VERSION=">= 7.0"
ARG REDIS_VERSION="7.0.5"
ARG RUBY_INSTALLER_VERSION="0.8.5"
ARG RUBY_VERSION="3.1.2"

ENV DEBIAN_FRONTEND=noninteractive

# Install system dependencies.
RUN apt update --quiet && \
    apt install --quiet --yes \
      bison \
      build-essential \
      g++ \
      git \
      gnupg2 \
      less \
      libffi-dev \
      libgdbm-dev \
      libncurses5-dev \
      libreadline-dev \
      libssl-dev \
      libyaml-dev \
      locales \
      lsb-release \
      make \
      tzdata \
      wget \
      zlib1g-dev

# Install PostgreSQL development and client libraries.
# See: https://wiki.postgresql.org/wiki/Apt
RUN wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | gpg --dearmor | tee /etc/apt/trusted.gpg.d/apt.postgresql.org.gpg > /dev/null && \
    echo "deb http://apt.postgresql.org/pub/repos/apt $(lsb_release -cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list && \
    apt update --quiet && \
    apt install --quiet --yes \
      libpq-dev \
      postgresql-client-${POSTGRESQL_VERSION}

# Install redis-cli the hard way.
RUN wget https://download.redis.io/releases/redis-${REDIS_VERSION}.tar.gz && \
    tar -xzvf redis-${REDIS_VERSION}.tar.gz && \
    make -C redis-${REDIS_VERSION} install redis-cli /usr/local/bin && \
    rm -rf redis-${REDIS_VERSION}*

# Create a folder to use as a persistent volume for caching dependencies.
RUN mkdir -p /usr/src/dependencies

# Download, verify, and install ruby-install
# See: https://github.com/postmodern/ruby-install
RUN wget -O ruby-install-${RUBY_INSTALLER_VERSION}.tar.gz https://github.com/postmodern/ruby-install/archive/v${RUBY_INSTALLER_VERSION}.tar.gz && \
    wget --quiet -O - https://raw.github.com/postmodern/postmodern.github.io/main/postmodern.asc | gpg --import && \
    wget https://raw.github.com/postmodern/ruby-install/master/pkg/ruby-install-${RUBY_INSTALLER_VERSION}.tar.gz.asc && \
    gpg --verify ruby-install-${RUBY_INSTALLER_VERSION}.tar.gz.asc ruby-install-${RUBY_INSTALLER_VERSION}.tar.gz && \
    tar -xzvf ruby-install-${RUBY_INSTALLER_VERSION}.tar.gz && \
    make -C ruby-install-${RUBY_INSTALLER_VERSION} install && \
    rm -rf ruby-install-${RUBY_INSTALLER_VERSION}*

# Install the version of Ruby defined at the top of this file.
RUN ruby-install --system ruby ${RUBY_VERSION}

# Silence Ruby deprecation warnings.
ENV RUBYOPT=-W:no-deprecated

# Install Bundler and configure it to use the persistent volume.
RUN gem install bundler && \
    bundle config path /usr/src/dependencies/bundler

# Install Node.js, enable the Yarn package manager, and configure Yarn to use
# the persistent volume..
# See: https://github.com/nodesource/distributions
RUN wget -O - https://deb.nodesource.com/setup_${NODE_VERSION} | bash - && \
    apt install --quiet --yes nodejs && \
    corepack enable && \
    yarn config set cache-folder /usr/src/dependencies/yarn

# Configure the American English locale and use UTF-8 encoding.
RUN localedef -i en_US -c -f UTF-8 -A /usr/share/locale/locale.alias en_US.UTF-8

ENV LANG=en_US.utf8

# Configure RubyGems to not install documentation, install the Foreman gem, and
# install the version of Rails specified at the top of this file.
RUN echo "gem: --no-document" >> ~/.gemrc && \
    gem install foreman && \
    gem install rails --version "${RAILS_VERSION}"

VOLUME /usr/src/dependencies

WORKDIR /usr/src/app

EXPOSE 3000

exec.sh

#!/usr/bin/env sh

# Rename this file to `bin/exec` and `chmod +x` it.

set -e

cmd=$*

container_name="jgarber623/thing-app"
container_id=$(docker ps --no-trunc --filter ancestor=${container_name} --format {{.ID}})

if [ -z "$cmd" ]; then
  echo "[ bin/exec ] 🚨 No command specified!"
  exit 1
fi

if [ -z $container_id ]; then
  echo "[ bin/exec ] 🚨 Couldn't find a container named \"$container_name.\" Have you run \"bin/start\" in another Terminal?"
  exit 1
else
  echo "[ bin/exec ] 🤖 Executing command \"$cmd\" inside container with ID = $container_id..."
  docker exec -it $container_id $cmd
fi

start.sh

#!/usr/bin/env sh

# Rename this file to `bin/start` and `chmod +x` it.

set -e

echo "[ bin/start ] 🐳 Running ./docker-compose.yml..."

# Forward arguments passed to this script. For example:
#
#  bin/start --build
#
docker compose up $@