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Docker : Docker Compose - Defining Multi-Container Applications

This article describes how to use Docker Compose to create multi-container applications.

Related articles.

Installation

Docker Compose can be downloaded from GitHub and the general installation instructions can be found here.

# curl -L https://github.com/docker/compose/releases/download/1.18.0/docker-compose-`uname -s`-`uname -m` -o /usr/local/bin/docker-compose
# chmod +x /usr/local/bin/docker-compose
# docker-compose -version
docker-compose version 1.18.0, build 8dd22a9
#

When we were setting up a non-root user for Docker (here) we did the following sudo and profile setup.

# useradd docker_user
# echo "docker_user  ALL=(ALL)  NOPASSWD: /usr/bin/docker" >> /etc/sudoers
# echo "alias docker=\"sudo /usr/bin/docker\"" >> /home/docker_user/.bash_profile
# su - docker_user

We can do a similar setup for Docker Compose too.

# echo "docker_user  ALL=(ALL)  NOPASSWD: /usr/local/bin/docker-compose" >> /etc/sudoers
# echo "alias docker-compose=\"sudo /usr/local/bin/docker-compose\"" >> /home/docker_user/.bash_profile
# su - docker_user
$ docker-compose -version
docker-compose version 1.18.0, build 8dd22a9
$

Defining Services

Services are typically defined using YAML in a "docker-compose.yml" file, though JSON files can also be used. The compose file reference, explains how the file is defined. Once you have manually run a couple of containers you will recognise most of the pieces. This file contains a definition of how to start each of the containers that make up the multi-container application, with their associated dependencies, networks and volumes etc.

As an example, check out this docker-compose.yml file, which builds a 12cR2 database container and an ORDS container, allowing you to run APEX applications.

You should navigate to the directory containing the "docker-compose.yml" file before running the following commands.

Starting Services

You can start a service by using the run, start or up commands, but you will typically use the docker-compose up command. By default it doesn't release the screen, but it can be detached using the "-d" option.

cd ~/dockerfiles/compose/ol7_122_ords

# Start containers and hold on to the screen.
docker-compose up

# Detach : Run containers in the background.
docker-compose up -d

Stopping Services

If you haven't used the "-d" option, you can use CTRL+C to gracefully stop the containers. If you did use the "-d" option, you will need to use the docker-compose stop command.

cd ~/dockerfiles/compose/ol7_122_ords

# Stop containers.
docker-compose stop

# Extend the timeout, which defaults to 10 seconds, to allow a graceful DB shutdown.
docker-compose stop -t 120
docker-compose stop --timeout 120

You could also remove the services with the stop option, described below.

Removing Services

Services are removed using the docker-compose rm command. It will remove any stopped containers associated with a service.

cd ~/dockerfiles/compose/ol7_122_ords

# Remove any stopped containers associated with services. Requires confirmation.
docker-compose rm

# No confirmation.
docker-compose rm -f
docker-compose rm --force

# Cleans up associated non-persistent volumes.
docker-compose rm -vf

# Stops the containers if necessary.
docker-compose rm -vsf
docker-compose rm -vf --stop

Remember, volumes defined in the "volumes:" section of the "docker-compose.yml" file are persistent, so they won't be removed by the "-v" option. This means they are safe for storing the database files in this example.

For more information see:

Hope this helps. Regards Tim...

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