example_dev_container.md

Example Container

Clone a repo todo_app in your local filesystem

git clone github:some_repo ./todo_app

Create a container

We are creating a new container based on ruby:2.7.2 image with volume mounted to our filesystem's todo_app folder in current working directory.

docker run -i -t --volume="$pwd":/todo_app -w /todo_app ruby:2.7.2 bin/bash

This will setup todo_app as working directory which will be prompted to us during start of the container.

If you exit this container and use the RUN command again, the changes will be lost, as it will create a completely new container.

Continue using the same container with exec

Use docker exec command to use the previous container you have built.

docker start $container_name
docker exec -i -t $container_name -w /todo_app $container_name bin/bash

Docker Compose

Typing all the commands and their options every time we work with container is cumbersome. Thus, Docker Compose comes into play where we create a configuration files that will ease things up when working with one or several containers.

Basic Docker Compose YML

# Version of the file
version: "1.0"
services:
  app: 
    image: "ruby:2.7.2"
    volumes:
      type: "bind"
      source: ..
      target: "/todo_app"
    working_dir: "/todo_app"
    # Let's container know to always run until interrupted.
    command: sleep infinity

docker compose up

docker compose exec app bin/bash

Build your own image with Dockerfile and set that up with Compose

If you would like to define the instructions and build your own custom image, you can create a Dockerfile and set that up in Docker Compose config.

<!-- Dockerfile -->
FROM ruby:2.7.2
RUN apt-get update
RUN apt-get install -y yarn

Prefer less RUN statements and try to join multiple commands with \ to reduce the Docker Layers, which will lead to more slimmer images.

version: "1.0"
services:
  app: 
    build:
      context: .
      dockerfile: Dockerfile
    volumes:
      type: "bind"
      source: ..
      target: "/todo_app"
    working_dir: "/todo_app"
    # Let's container know to always run until interrupted.
    command: sleep infinity

Port Mapping

version: "3.2"
services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
  volumes:
    - type: bind
    source: ..
    target: /workspace
  working_dir: /workspace
  command: sleep infinity
  ports:
    # Don't forget to bind the puma server to 0.0.0.0 instead of loopback 127.0.0.1
    - "3000:3000"