I often see articles about running Ruby on Rails with Docker, but I don't see padrino so much, so a memo of the procedure when I tried it after studying.
Creating a Docker image is a bit cumbersome because the padrino g project forces a subdirectory to be created.
Windows10 Home Edition
VirtualBox 6.1.10
# Docker Host OS (CoreOS)
$ uname -a
Linux default 4.9.93-boot2docker #1 SMP Thu Jul 19 18:29:50 UTC 2018 x86_64 GNU/Linux
Docker version 18.06.1-ce, build e68fc7a
docker-compose version 1.20.1, build 5d8c71b
padrino g project (called the base image)base image and copy the initial project folder to the host OS side with docker cpbase image (called the ʻapp` image)Since the subdirectory is created by padrino g project, WORKDIR changes before and after the project is created, so the above procedure is taken.
Initially only docker-compose.yml and Dockerfile in the padrino folder
padrino
|   docker-compose.yml
|   Dockerfile
docker-compose.yml
Contents for creating a base image
docker-compose.yml
version: "3.4"
services:
  base: 
    build:
      context: .
      dockerfile: ./Dockerfile
      target: "padrino-base"
    image: takaya030/padrino-base
    ports: 
      - "3000:3000"
    working_dir: /workspace/myapp
    command: "bundle exec padrino s -h 0.0.0.0"
Dockerfile
This is also the content for creating a base image
Dockerfile
FROM ruby:2.7.1 as padrino-base
LABEL maintainer "takaya030"
RUN apt-get update -qq && \
    apt-get install -y build-essential libpq-dev nodejs && \
	apt-get clean && \
	rm -rf /var/lib/apt/lists/*
# insall padrino
RUN mkdir /workspace
WORKDIR /workspace
RUN bundle init && \
	echo 'gem "padrino"' >>Gemfile && \
	bundle config set path 'vendor/bundle' && \
	bundle install && \
	bundle exec padrino g project myapp -t rspec -e erb -c sass -s jquery -d activerecord && \
	rm -rf Gemfile Gemfile.lock .bundle vendor
# create project
WORKDIR /workspace/myapp
RUN bundle config set path 'vendor/install' && \
	bundle install
CMD ["true"]
base image$ cd padrino
$ docker-compose build base
base imageStart Docker container
$ docker-compose up -d
If you access http://192.168.99.100:3000/ with a web browser and the following is displayed, it is working properly.

Stop the container once
$ docker-compose stop
Copy the project folder in the stopped container to the host OS side This is the actual development environment
$ docker cp padrino_base_1:/workspace/myapp .
# "padrino_base_1"Is the name of the container you just stopped
When the copy is completed, the development environment will be created under the padrino / myapp / folder.
padrino
|   docker-compose.yml
|   Dockerfile
|   
\---myapp
Delete the container when the copy is complete
$ docker-compose rm
docker-compose.yml
Change to the following contents
docker-compose.yml
version: "3.4"
services:
  base: 
    build:
      context: .
      dockerfile: ./Dockerfile
      target: "padrino-base"
    image: takaya030/padrino-base
  app: 
    build:
      context: .
      dockerfile: ./Dockerfile
      target: "padrino-app"
    image: takaya030/padrino-app
    ports: 
      - "3000:3000"
    volumes:
      - ./myapp:/workspace/myapp
    working_dir: /workspace/myapp
    command: "bundle exec padrino s -h 0.0.0.0"
Dockerfile
Change to the following contents
Dockerfile
FROM ruby:2.7.1 as padrino-base
LABEL maintainer "takaya030"
RUN apt-get update -qq && \
    apt-get install -y build-essential libpq-dev nodejs && \
	apt-get clean && \
	rm -rf /var/lib/apt/lists/*
# insall padrino
RUN mkdir /workspace
WORKDIR /workspace
RUN bundle init && \
	echo 'gem "padrino"' >>Gemfile && \
	bundle config set path 'vendor/bundle' && \
	bundle install && \
	bundle exec padrino g project myapp -t rspec -e erb -c sass -s jquery -d activerecord && \
	rm -rf Gemfile Gemfile.lock .bundle vendor
# create project
WORKDIR /workspace/myapp
RUN bundle config set path 'vendor/install' && \
	bundle install
CMD ["true"]
#=========================================
FROM padrino-base as padrino-app
COPY ./myapp /workspace/myapp
WORKDIR /workspace/myapp
CMD ["bundle","exec","padrino","s","-h","0.0.0.0"]
$ docker-compose build app
Start Docker container
$ docker-compose up -d
Go to http://192.168.99.100:3000/ with a web browser and check that the same screen as before is displayed.
With the container running, change myapp / app / app.rb as follows
myapp/app/app.rb
--- a/app.rb      Sat Jun 06 19:19:23 2020
+++ b/app.rb      Sat Jun 06 22:30:27 2020
@@ -62,5 +62,10 @@
     #     render 'errors/500'
     #   end
     #
+
+    get '/' do
+      "Hello World"
+    end
+
   end
 end
If you access http://192.168.99.100:3000/ again with a web browser and it is displayed as shown in the image below, it is working normally.

Check currently installed packages
$ docker-compose run --rm app bundle list
Gems included by the bundle:
  * activemodel (6.0.3.1)
  * activerecord (6.0.3.1)
  * activesupport (6.0.3.1)
  * concurrent-ruby (1.1.6)
  * diff-lcs (1.3)
  * erubi (1.9.0)
  * ffi (1.13.0)
  * i18n (1.8.3)
  * mail (2.7.1)
  * mime-types (3.3.1)
  * mime-types-data (3.2020.0512)
  * mini_mime (1.0.2)
  * minitest (5.14.1)
  * moneta (1.1.1)
  * mustermann (1.1.1)
  * padrino (0.15.0)
  * padrino-admin (0.15.0)
  * padrino-cache (0.15.0)
  * padrino-core (0.15.0)
  * padrino-gen (0.15.0)
  * padrino-helpers (0.15.0)
  * padrino-mailer (0.15.0)
  * padrino-support (0.15.0)
  * rack (2.2.2)
  * rack-protection (2.0.8.1)
  * rack-test (1.1.0)
  * rake (13.0.1)
  * rb-fsevent (0.10.4)
  * rb-inotify (0.10.1)
  * rspec (3.9.0)
  * rspec-core (3.9.2)
  * rspec-expectations (3.9.2)
  * rspec-mocks (3.9.1)
  * rspec-support (3.9.3)
  * ruby2_keywords (0.0.2)
  * sass (3.7.4)
  * sass-listen (4.0.0)
  * sinatra (2.0.8.1)
  * sqlite3 (1.4.2)
  * thor (0.20.3)
  * thread_safe (0.3.6)
  * tilt (2.0.10)
  * tzinfo (1.2.7)
  * zeitwerk (2.3.0)
Use `bundle info` to print more detailed information about a gem
Describe the package you want to add to myapp / Gemfile
myapp/Gemfile
--- a/Gemfile     Sat Jun 06 19:19:23 2020
+++ b/Gemfile     Sun Jun 07 21:57:33 2020
@@ -22,6 +22,10 @@
 gem 'activerecord', '>= 3.1', :require => 'active_record'
 gem 'sqlite3'
+# OAuth
+gem "omniauth"
+gem "omniauth-twitter"
+
 # Test requirements
 gem 'rspec', :group => 'test'
 gem 'rack-test', :require => 'rack/test', :group => 'test'
Install the package with the following command
$ docker-compose run --rm app bundle install
Check if it was installed successfully (Confirm that ʻomniauth` related packages have been added)
$ docker-compose run --rm app bundle list
Gems included by the bundle:
  * activemodel (6.0.3.1)
  * activerecord (6.0.3.1)
  * activesupport (6.0.3.1)
  * concurrent-ruby (1.1.6)
  * diff-lcs (1.3)
  * erubi (1.9.0)
  * ffi (1.13.0)
  * hashie (4.1.0)
  * i18n (1.8.3)
  * mail (2.7.1)
  * mime-types (3.3.1)
  * mime-types-data (3.2020.0512)
  * mini_mime (1.0.2)
  * minitest (5.14.1)
  * moneta (1.1.1)
  * mustermann (1.1.1)
  * oauth (0.5.4)
  * omniauth (1.9.1)
  * omniauth-oauth (1.1.0)
  * omniauth-twitter (1.4.0)
  * padrino (0.15.0)
  * padrino-admin (0.15.0)
  * padrino-cache (0.15.0)
  * padrino-core (0.15.0)
  * padrino-gen (0.15.0)
  * padrino-helpers (0.15.0)
  * padrino-mailer (0.15.0)
  * padrino-support (0.15.0)
  * rack (2.2.2)
  * rack-protection (2.0.8.1)
  * rack-test (1.1.0)
  * rake (13.0.1)
  * rb-fsevent (0.10.4)
  * rb-inotify (0.10.1)
  * rspec (3.9.0)
  * rspec-core (3.9.2)
  * rspec-expectations (3.9.2)
  * rspec-mocks (3.9.1)
  * rspec-support (3.9.3)
  * ruby2_keywords (0.0.2)
  * sass (3.7.4)
  * sass-listen (4.0.0)
  * sinatra (2.0.8.1)
  * sqlite3 (1.4.2)
  * thor (0.20.3)
  * thread_safe (0.3.6)
  * tilt (2.0.10)
  * tzinfo (1.2.7)
  * zeitwerk (2.3.0)
Use `bundle info` to print more detailed information about a gem
-How to get started with Padrino-- Qiita -Try using Padrino without polluting the environment --Qiita -Create a development environment with Docker Compose by making the DB withdrawn in the application server independent --Qiita
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