Dockerfile for Rails app

config|nginx|default

upstream app {
    # Path to Puma SOCK file, as defined previously
    server unix:/sockets/puma.sock fail_timeout=0;
}

server {
    listen 80;
    server_name localhost;

    root /project/public;

    try_files $uri/index.html $uri @app;

    location @app {
        proxy_pass http://app;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_redirect off;
    }

    error_page 500 502 503 504 /500.html;
    client_max_body_size 4G;
    keepalive_timeout 10;
}

config|puma|development.rb

# Puma can serve each request in a thread from an internal thread pool.
# The `threads` method setting takes two numbers a minimum and maximum.
# Any libraries that use thread pools should be configured to match
# the maximum value specified for Puma. Default is set to 5 threads for minimum
# and maximum, this matches the default thread size of Active Record.
#
threads_count = ENV.fetch("RAILS_MAX_THREADS") { 3 }.to_i
threads 1, threads_count

# Specifies the `port` that Puma will listen on to receive requests, default is 3000.
#
port        ENV.fetch("PORT") { 3000 }

# Specifies the `environment` that Puma will run in.
#
environment ENV.fetch("RAILS_ENV") { "development" }

# Specifies the number of `workers` to boot in clustered mode.
# Workers are forked webserver processes. If using threads and workers together
# the concurrency of the application would be max `threads` * `workers`.
# Workers do not work on JRuby or Windows (both of which do not support
# processes).
#
workers ENV.fetch("WEB_CONCURRENCY") { 2 }

# Use the `preload_app!` method when specifying a `workers` number.
# This directive tells Puma to first boot the application and load code
# before forking the application. This takes advantage of Copy On Write
# process behavior so workers use less memory. If you use this option
# you need to make sure to reconnect any threads in the `on_worker_boot`
# block.
#
# preload_app!

# The code in the `on_worker_boot` will be called if you are using
# clustered mode by specifying a number of `workers`. After each worker
# process is booted this block will be run, if you are using `preload_app!`
# option you will want to use this block to reconnect to any threads
# or connections that may have been created at application boot, Ruby
# cannot share connections between processes.
#
# on_worker_boot do
#   ActiveRecord::Base.establish_connection if defined?(ActiveRecord)
# end

# Allow puma to be restarted by `rails restart` command.
plugin :tmp_restart

config|puma|production.rb

# Puma can serve each request in a thread from an internal thread pool.
# The `threads` method setting takes two numbers a minimum and maximum.
# Any libraries that use thread pools should be configured to match
# the maximum value specified for Puma. Default is set to 5 threads for minimum
# and maximum, this matches the default thread size of Active Record.

threads_count = ENV.fetch('RAILS_MAX_THREADS') { 5 }.to_i
threads 1, threads_count

# Specifies the `port` that Puma will listen on to receive requests, default is
# 3000.

# port ENV.fetch('PORT') { 3000 }

# Set up socket location
bind 'unix:///sockets/puma.sock'

# Specifies the `environment` that Puma will run in.

environment ENV.fetch('RAILS_ENV') { 'production' }

# Specifies the number of `workers` to boot in clustered mode.
# Workers are forked webserver processes. If using threads and workers together
# the concurrency of the application would be max `threads` * `workers`.
# Workers do not work on JRuby or Windows (both of which do not support
# processes).

workers ENV.fetch('WEB_CONCURRENCY') { 2 }

# Use the `preload_app!` method when specifying a `workers` number.
# This directive tells Puma to first boot the application and load code
# before forking the application. This takes advantage of Copy On Write
# process behavior so workers use less memory. If you use this option
# you need to make sure to reconnect any threads in the `on_worker_boot`
# block.

preload_app!

# The code in the `on_worker_boot` will be called if you are using
# clustered mode by specifying a number of `workers`. After each worker
# process is booted this block will be run, if you are using `preload_app!`
# option you will want to use this block to reconnect to any threads
# or connections that may have been created at application boot, Ruby
# cannot share connections between processes.

on_worker_boot do
  ActiveRecord::Base.establish_connection if defined?(ActiveRecord)
end

before_fork do
  ActiveRecord::Base.connection_pool.disconnect! if defined?(ActiveRecord)
end

# Allow puma to be restarted by `rails restart` command.
# plugin :tmp_restart

Dockerfile

# Use the barebones version of Ruby 2.2.3.
FROM ruby:2.7.6

# Optionally set a maintainer name to let people know who made this image.
# MAINTAINER

# Install dependencies:
# - build-essential: To ensure certain gems can be compiled
# - nodejs: Compile assets
# - libpq-dev: Communicate with postgres through the postgres gem
# - postgresql-client-9.4: In case you want to talk directly to postgres
RUN apt-get update && apt-get install -qq -y build-essential nodejs libpq-dev --fix-missing --no-install-recommends
RUN apt-get install -qq -y nginx --fix-missing --no-install-recommends
RUN mkdir /sockets

# Set an environment variable to store where the app is installed to inside
# of the Docker image.
ENV INSTALL_PATH /project
RUN mkdir -p $INSTALL_PATH
RUN mkdir -p $INSTALL_PATH/tmp/pids

# This sets the context of where commands will be ran in and is documented
# on Docker's website extensively.
WORKDIR $INSTALL_PATH

# Ensure gems are cached and only get updated when they change. This will
# drastically increase build times when your gems do not change.
COPY Gemfile Gemfile
COPY Gemfile.lock Gemfile.lock
RUN gem install bundler --version 1.17.3
RUN bundle config build.nokogiri --use-system-libraries
RUN bundle install --without test development

# Copy in the application code from your work station at the current directory
# over to the working directory.
COPY . .

# Copy nginx config
COPY ./config/nginx/default /etc/nginx/sites-available/default

ENV RAILS_ENV production

RUN bin/rails assets:precompile

# Expose a volume so that nginx will be able to read in assets in production.
VOLUME ["$INSTALL_PATH/public"]

# Start servers
CMD bundle exec puma -C config/puma/production.rb
# CMD service nginx restart