How to use Docker Compose

Given problem
Solution with Docker Compose
How to create docker-compose.yaml file
Wrapping up

Given problem

Before going to this article, we can read up on the article Understanding about Docker. In that article, we can learn about how to run an image an a container.

But if in our project, we have multiple softwares or multiple images, then when we deploy our application, we need to deploy sequentially each container. It takes so much our time and effort. To reduce the hard working time, we can use docker-compose.

So, how docker-compose work?

Solution with Docker Compose

To manage all containers that we want to run through Docker, we will define docker-compose.yaml file. It will contains definition of all images that we want to use such as image name, container name when it run, ports, …

After defining docker-compose.yaml file completely, we will use docker-compose tool to read that file and deploy them.

Setup docker compose tool
- In Windows OS, by default, when we install Docker, docker compose tool will also be installed.
- In Ubuntu OS, Docker and Docker compose will be installed seperately.
  
  Belows are some steps that install docker compose tool.
  - Check the current version of docker-compose:
    sudo curl -L https://github.com/docker/compose/releases/download/1.21.2/docker-compose-`uname -s`-`uname -m` -o / usr / local / bin / docker-compose
  - Set the permissions:
    sudo chmod + x / usr / local / bin / docker-compose
  - Verify whether docker compose is installed successfully:
    docker-compose --version
How Docker Compose tool works
- First, this tool will build an image from the source code or pull an image from Docker Hub.
- Then, run them as containers with ports, environment variables, … that are configured in docker-compose.yaml file.

How to create docker-compose.yaml file

Before creating docker-compose.yaml file, we need to understand some parameters that will be used in it.

verison

The current version of docker-compose that we are using.
services

All the containers that we want to utilize.
image

Images will be used when creating containers.
build

This option will be used to build an image from the source code by reading its DockerFile, then run as a container.
ports

It is used to define the port of host and port of container.

For example:
```
 ports:
     - 3306:3306
```
restart

When a container was turned off, immediately it will be started.
environment

This parameter will define multiple environment variables for our container.
depends_on

It points to the dependence between services. For example, before a service can be run, it need other services to run.
volumnes

They are physical areas of disk space shared between the host and a container, or even between containers. So, volumne is a shared directory in the host visible from some or all containers.

It will exchange two folders in host and container.
container_name

It points the name for our container.

networks

It defines the communication rules between containers, and between a container and a host. Common network zones will make containers’ services discoverable by each other, while private zones will segregate them in virtual sandboxes.

It means that we only need to define the name for networks that will be used to communicate between multiple containers, or define the private network for one container.

version: '3.0'

services:
    service_a:
        image: image_service_a
        networks:
            - shared_networks

    service_b:
        image: image_service_b
        networks:
            - shared_networks

    service_c:
        image: image_service_c
        networks:
            - private_networks

networks:
    shared_networks: {}
    private_networks: {}

expose

It will document the host port.

So, to run docker-compose.yaml file, we can run a below command line.

# running docker-compose file
docker-compose up

# running containers in detach mode or background
docker-compose up -d

# stop containers
docker-compose stop

# list all enviroment variables in a specific container
docker-compose run <container_name> env

# remove all containers in docker
docker-compose down --volumes