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Docker Compose

This is a working document from my own experience using Docker, so I update it when I discover new things. If you see any errors or improvements, please do comment.

Docker Compose is great because you can link several containers in one docker-compose file that takes care of pulling, buliding and running all of containers from one command: sudo docker-compose up or sudo docker-compose up -d (for background running)

I use Docker (version: 2.17.2) on Manjaro Linux, which is a fork of Arch. I recently installed Docker (version: 1.29.2) on Ubuntu , running on a virtual machine for testing.

On my Manjaro box I can use the command docker compose up, but on Ubuntu, I have to use sudo docker-compose up. I'm just creating awareness that systems, versions and setups differ. It seems that if you have Docker Compose < version 2, a hyphen in docker-compose is required.

NOTE: To not have to type in sudo for every command, add your user to the docker group.

sudo usermod -aG docker your_user

You need to log out and in again, or execute newgrp docker in the terminal to apply the change.. Now, you don't need to type sudo to run docker-compose / docker compose commands.

Installation

You can install Docker Compose along with Docker, but if you already have Docker, just install Docker Compose.

You can use a GUI software manager or a terminal.

Debian

sudo apt install docker docker-compose

Arch

sudo pacman -S docker docker-compose

Set Up a Project

docker-compose.yaml

Docker Compose searches for a file named docker-compose.yaml, which is where our docker image configuration instructions are. Some images are built from a Dockerfile as well, but we don't need one for MySQL. We will look more into docker-compose.yaml later, but first let's get the directories sorted out.

  1. create a new project directory: mkdir directory_name

  2. Change to the directory: cd directory_name

  3. Create a new file: touch docker-compose.yaml

  • NOTE: you could open an empty file with a text editor:

nano docker-compose.yaml

  1. Here is a docker-compose.yaml similar to the file I used to create my MySQL container named my_database which creates a database named pies.
version: "3"

services:
  data:
    image: mysql
    container_name: my_database
    environment:
      MYSQL_DATABASE: pies
      MYSQL_ROOT_PASSWORD: 'gren5432ko'
      MYSQL_USER: norooty
      MYSQL_PASSWORD: 'gkke532lro'
    volumes:
      - ./mysql:/var/lib/mysql
    ports:
      - 3306:3306

What does the file do?

Version and services are required.

  • data: this the name you give to the service. It could be named db, mysql, whatever_you_want.

    • The label is used when linking to other containers in the image.

  • image: instructs Docker Compose to pull (download) MySQL from Docker Hub.

  • container_name: gives the Docker container a custom name, which will be used later.

  • environment: sets up the database and in this case:

    • MYSQL_DATABSAE: Creates a new database during the build process

    • MYSQL_ROOT_PASSWORD: sets a root password for the database

    • MYSQL_USER: creates a non-root user

    • MYSQL_PASSWORS: sets the non-root user's password

  • volumes: maps a local directory in our project folder (or any other directory you define) to where MySQL works from in the container, a bit like syncing. This persists the data locally as well as volatile in the container, so if we remove the container, we can rebuild it with data from the local directory during the build process.

    • Syntax: local_directory:container_directory

    • The ./mysql part creates a new directory in the project directory :/var/lib/mysql is were any data will be synched from in the container.

    • The name of the local directory can be anything that is meaningful.

  • ports: MySQL's default port is 3306. To reach it from our host, we need to map it to port 3306 (or any other port) on our machine.

  • local_port:container_port

Building the Image

To build the docker image, depending on your set up: sudo docker-compose up or sudo docker compose up

You can use sudo docker-compose up to start docker with rebuild if changes are detected in the docker-compose.yaml file. To only start the container, type, sudo docker-compose start.

Docker Compose will build and start the container. We can check the container is running with: sudo docker ps.

In the last column, you should see the container name.

NAMES  
my_database

Accessing MySQL

You can set up MySQL Workbench as you would in any case, but set the host to 127.0.0.1 NOT localhost.

I will use the information from the docker-compose.yaml configuration above.

To use MySQL in a terminal, we need to command Docker to execute MySQL:

Make sure the terminal is in the project directory.

sudo docker exec -it my_database mysql -u norooty -p

The syntax is [sudo docker exec -it] [container_name] [app_to_run] [app options]

I'm sure you don't want to enter that line every time, so let's create a BASH script. I'm not sure about ZSH scripts. BASH scripts use the .sh file extension.

In the project folder, create a new file with a short name. I named mine, go_sql.sh.

Open the file with these contents (change according to your configuration):


#!/bin/bash

sudo docker exec -it my_database mysql -u norooty -p

  • exec: tells Docker to execute the command

  • -it: makes the shell interactive

  • my_database: the container name

  • mysql: what we want Docker to run with the container

    • -u: mysql user name
    • norooty: the non-root username
    • -p: This produces a password prompt in the terminal

  • Save and exit the file.

  • Set the file permissions to 771: chmod 771 go_mysql.sh If anyone knows more about that, please comment.

Now, you can start a MySQL shell, while in the project directory with ./go_mysql.sh.

Stopping the Container

To stop a container if you started it with docker-compose up, you will see activity output to the terminal. Press CTRL + C.

If you started it with sudo docker-compose up -d, there is no logs output. Type, sudo docker-compose stop

Removing a Container

To remove a container, not including persistent data in the local directory, type, sudo docker-compose down

Start a Container

You can use sudo docker-compose up or sudo docker-compose up -d

up will check for changes in the docker-compose.yaml file and recreate the container if needed.

-d runs Docker in the background.

Docker may be started without checking for changes, with sudo docker-compose start

Docker Compose up Issues

Changing the default database name

I have discovered that when the name of the default MySQL database is changed in the docker-compose.yaml file (MYSQL_DATABASE:), during the next execution of docker-compose up (changes usually supercede previous configurations), the new default database is not created in the locally mapped directory. I have found two ways around this.

WARNING: The following command will remove the persisted database data. The local directory that is mapped needs to be deleted, which allows Docker Compose to recreate it with the new database environment. Run sudo rm -r local_directory. In the example case above, sudo rm -r mysql

ALTERNATIVE If you want to keep the existing database environment and have another one with a different name in the same container, do these things:

  • Change the name of the MYSQL_DATABASE
  • Change the name of the local mapped directory (./mysql:/usr/var/mysql), which will create a new one when docker-compose up is executed. It is then possible to switch between default databases.

Docker Compose creates another sub-directory with the new name.

That should cover most things to get a Docker Compose image up and running with one container.

Docker images are found on Docker Hub.