Minimal Sinatra Application on Docker

app.rb

class App < Sinatra::Base
  get "/" do
    "hello"
  end
end

config.ru

require "bundler"
Bundler.require

require "./app.rb"
run App

Dockerfile

FROM ruby:2.2.0

RUN bundle config --global frozen 1

RUN mkdir -p /usr/src/app
WORKDIR /usr/src/app

ADD Gemfile /usr/src/app/
ADD Gemfile.lock /usr/src/app/
RUN bundle install --without test development --system

ADD . /usr/src/app

RUN apt-get update && apt-get install -y nodejs --no-install-recommends && rm -rf /var/lib/apt/lists/*

EXPOSE 9292
CMD ["bundle", "exec", "rackup", "-p", "9292", "-E", "production"]

Gemfile

source "https://rubygems.org"

gem "sinatra", "~> 1.4.5"

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    rack (1.6.0)
    rack-protection (1.5.3)
      rack
    sinatra (1.4.5)
      rack (~> 1.4)
      rack-protection (~> 1.4)
      tilt (~> 1.3, >= 1.3.4)
    tilt (1.4.1)

PLATFORMS
  ruby

DEPENDENCIES
  sinatra (~> 1.4.5)