Multi-container applications

The example in the previous section was fun but did not really gain us anything over using the docker command. Most Internet applications have multiple pieces. The most common example is a web application that loads data from a database.

In ch02/web-db of the docker-orchestration-examples repository there is a very simple application that loads a list of authors and books from MySQL and displays them on a web page. Here is a docker-compose.yml that defines the application:

version: '2' 
 
services: 
  web: 
    image: web-db:0.1 
    build: . 
    ports: 
      - 80:5000 
    env_file: 
      - db.env 
    entrypoint: ./start.pl --init --command shotgun 
  db: 
    image: mysql:5.7 
    env_file: 
      - db.env 

The first thing that you should notice is that there are two services defined. The first, web, is the web application. The second, db, is a MySQL container. Let's look at them one at a time.

The build key tells docker-compose that this service...