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Docker Compose
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.. contents:: Table of Contents


Docker Compose is a Docker tool that allows us to configure a
Docker project. The tool takes care of starting and stopping
the project. It builds and dynamically links the various
containers defined in the configuration files. We need to
understand the configuration parameters and know the commands to run.

.. code-block:: bash

    docker-compose up -d     # Creates and starts the Docker project in daemon mode.
    docker-compose start     # Starts images that were running but are now stopped.

    docker-compose stop      # Stops the project but keeps the containers.

    docker-compose down      # Stops the project and removes the containers.
    docker-compose down -v   # Stops the project, removes the containers, and remove the volume data.

Now, let's look at the
:ref:`WordPress project from lab 2 <simple-wp-in-using-docker-compose>`.

1. We will configure ``docker-compose.yml`` to include a volume that
   will persist the web data on the VPS.
2. We will add components to the ``docker-compose.yml`` file, which
   become containers. Specifically, we will add a memory caching
   service called `Redis`.

.. _default-wp-docker-compose:

**File contents of 'docker-compose.yml'**

.. code-block:: bash

    version: '3.3'

    services:
       db:
         image: mysql:5.7
         volumes:
           - db_data:/var/lib/mysql
         restart: always
         environment:
           MYSQL_ROOT_PASSWORD: somewordpress
           MYSQL_DATABASE: wordpress
           MYSQL_USER: wordpress
           MYSQL_PASSWORD: wordpress

       wordpress:
         depends_on:
           - db
         image: wordpress:latest
         ports:
           - "20851:80"
         restart: always
         environment:
           WORDPRESS_DB_HOST: db:3306
           WORDPRESS_DB_USER: wordpress
           WORDPRESS_DB_PASSWORD: wordpress
           WORDPRESS_DB_NAME: wordpress

    volumes:
        db_data: {}


Here is some information about parts of the file:

1. **services**: Describe the different images the application depends on

   - This project has 2 services: ``db`` and ``wordpress``
   - Each service has its own Docker container.

#. **ports**: These come in pairs. ``20851:80``

   - The left value (20851) is the external port. This is how
     you access the service.
   - Docker will bind to this external port. No other service can use it,
     just like with port 80.
   - The right value (80) is the internal port to the docker container.

#. **environment**: Contains environmental variables, such as passwords
   or connection information
#. **volumes**: Indicates where the data is stored.

   - A powerful feature of Docker is that the data can be stored on
     the host machine.
   - A Docker container can be added and removed without destroying the data.