Prerequisites

• A Webdock cloud Ubuntu instance (18.04 or later)

• You have shell (SSH) access to your VPS

• Docker installed on your Ubuntu instance

Disclaimer

Docker under-the-hood manages iptables based on the ports published during the creation of containers. Do not expose ports on all interfaces if you do not want to expose a port publicly, instead use something like a "-p 127.0.0.1:80:80" to expose the port only on localhost (in this case the port is 80. For simplicity sake, you want to publish on all interfaces but block public access, you need to explicity block the port using a firewall like UFW.

This guide on UFW might help.

Installing docker-compose

First, remove the old version of docker-compose if installed.

$ sudo apt remove docker-compose

Download the current stable release of docker-compose.

$ sudo curl -L "https://github.com/docker/compose/releases/download/v2.12.2/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

Note: Please check the GitHub repo for the latest stable docker-compose binary. Replace the v2.12.2 in the above URL to fetch another version of docker-compose.

Apply execute permissions to the downloaded binary.

$ sudo chmod +x /usr/local/bin/docker-compose

Create a symlink to /usr/bin directory.

$ sudo ln -s /usr/local/bin/docker-compose /usr/bin/docker-compose

Check the docker-compose version to verify installation.

$ docker-compose --version

Creating docker-compose file

First create a new directory on your Webdock instance and go inside this directory.

$ mkdir ~/docker-compose
$ cd ~/docker-compose

Create a new file named docker-compose.yml.

$ touch docker-compose.yml

Open the file in your favorite editor.

$ nano docker-compose.yml

The docker-compose.yml file, as the name describes, is a file written in YAML format. The first option in this file is the compose version.

The version describes the compose file format for a specific version. It can be added in the compose file as below.

version: "3.8"

The compose file can contain configuration for multiple services (docker containers). These services are defined under the services option.

version: "3.8"

services:

  mysql_service:

Now under the mysql_service option, we will add mysql container options as key value pairs. The important options are

• image: This describes which docker image will be used for this specific service.

• container_name: Specifies the name of the docker container.

• restart: It specifies the container restart policy. There are four values for this option.
  • no → docker container will not start after it stops.
  • unless-stopped → docker container restarts after application crashes or process ends. But will not start after it is manually stopped.
  • always → docker container always restarts after docker service is restarted even if you manually stop it.
  • on-failure → docker container will only restart when an application crashes inside the container.

• ports: It is the list of port mappings from docker container to docker host.

• environment: It takes a list of environment variables passed inside the container.

• volumes: This option accepts a list of volumes mounted from docker container to docker host.

• networks: This option also specifies a list of different networks the docker container will be part of.

So the final compose file for mysql service will look like this.

version: "3.8"

services:

   mysql_service:

    image: mysql:8.0.23

    container_name: mysql

    restart: unless-stopped

    ports:

        - "3300:3306"

    environment:

        - MYSQL_ROOT_PASSWORD=super-secret-password

        - MYSQL_DATABASE=webdock

    volumes:

        - mysql-vol:/var/lib/mysql

    networks:

        - webdock


networks:

    webdock:

volumes:

   mysql-vol:

The volumes and networks used inside the compose file must be initialized at the end of the compose file.

The above compose file will create a docker network named webdock and a docker volume named mysql-vol.

After this, it will create a docker container named mysql from mysql:8.0.23 docker image. By default the docker image is pulled from DockerHub.

The port 3306 of the created docker container will be mapped to the port 3300 of the docker host (Webdock instance).

This compose file will set the root password of the mysql database to super-secret-password and an initial database named webdock will be created.

The /var/lib/mysql directory inside the docker container will be mapped to the mysql-vol docker volume on docker host for data persistence.

This container will be part of the newly created docker network named webdock. If you run another container inside the same network, these two containers will be able to communicate with each other by their container names.

Running docker-compose

Now save the file and run the following command to create the docker container using docker-compose.

$ docker-compose up

It will run the docker-compose in the foreground and you can not exit the terminal. To run the compose in background, add the -d option with the command.

$ docker-compose up -d

If the docker-compose.yml file is not present in the current working directory or the name of the file is other than docker-compose.yml, use the -f option to specify the compose file.

$ docker-compose -f ~/docker-compose/docker-compose.yml up -d

After running compose, check the status of the docker container.

$ docker-compose ps

OR

$ docker-compose -f ~/docker-compose/docker-compose.yml ps

Check the logs of the containers for debugging.

$ docker-compose logs

OR

$ docker-compose -f ~/docker-compose/docker-compose.yml logs

Conclusion

Compose is a tool used to configure containerized microservices using a simple configuration file. It makes the process easier to deploy a containerized application on the server. This article described how a compose file is written to deploy containerized applications.