How to Configure Docker Compose for Multi-Container Applications

How to Configure Docker Compose for Multi-Container Applications

Step 1: Install Docker and Docker Compose

• Install Docker:
  • Update your package list:

    sudo apt-get update
    

  • Install Docker with the following command:

    sudo apt-get install docker.io
    

  • Start Docker and enable it to launch at boot:

    sudo systemctl start docker
    sudo systemctl enable docker
    

  • Verify the installation:

    docker --version
    

• Install Docker Compose:
  • Download the latest version of Docker Compose:

    sudo curl -L "https://github.com/docker/compose/releases/download/$(curl -s https://api.github.com/repos/docker/compose/releases/latest | jq -r .tag_name)/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
    

  • Make Docker Compose executable:

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

  • Verify the installation:

    docker-compose --version
    

Step 2: Create a Docker Compose Configuration File

• Create a docker-compose.yml file in your project directory:

  nano docker-compose.yml
  

• Define your services (containers) in the YAML file. Here’s a basic example with two containers (a web server and a database):

  version: '3'
  services:
    web:
      image: nginx
      ports:
        - "80:80"
    db:
      image: mysql:5.7
      environment:
        MYSQL_ROOT_PASSWORD: example
  

  • This configuration sets up an Nginx web server and a MySQL database.
  • The web container listens on port 80 and the db container uses a password for the root user.

Step 3: Start the Multi-Container Application

• Run the following command to start the services defined in your docker-compose.yml file:

  docker-compose up -d
  

  • The -d flag runs the containers in detached mode (in the background).
  • Docker Compose will automatically download the required images and create containers as defined.

Step 4: Verify the Running Containers

• Check the status of the containers:

  docker-compose ps
  

  • This will show you the list of running containers along with their respective status and port mappings.
• You can also check logs for any issues:

  docker-compose logs
  

Step 5: Interact with Containers

• You can access a running container using the following command:

  docker exec -it <container_name> /bin/bash
  

  • Replace <container_name> with the name of your container (e.g., web or db).
  • This will open a shell session inside the container, allowing you to interact with it directly.

Step 6: Scaling the Application

• Docker Compose allows you to scale services horizontally. For example, to run multiple instances of the web server:

  docker-compose up -d --scale web=3
  

  • This command will create 3 instances of the web service (Nginx).
• Verify the scaling:

  docker-compose ps
  

Step 7: Updating the Application

• If you need to update your containers (e.g., update the image or change configurations), modify the docker-compose.yml file and run:

  docker-compose up -d
  

  • Docker Compose will automatically apply the changes to the running containers.

Step 8: Stopping and Removing Containers

• To stop the running containers, use:

  docker-compose down
  

  • This will stop and remove all the containers, networks, and volumes defined in your docker-compose.yml file.

Step 9: Clean Up Resources

• If you want to remove containers, networks, and volumes completely, run:

  docker-compose down --volumes --remove-orphans
  

  • This will also remove any unused volumes and orphaned containers.

Step 10: Automating Docker Compose with Systemd (Optional)

• For automatic startup of your application when the server reboots, you can create a systemd service file:
  • Create a new service file:

    sudo nano /etc/systemd/system/docker-compose-app.service
    

  • Add the following content to it:

    [Unit]
    Description=Docker Compose Application
    After=docker.service
    Requires=docker.service
    
    [Service]
    WorkingDirectory=/path/to/your/project
    ExecStart=/usr/local/bin/docker-compose up
    ExecStop=/usr/local/bin/docker-compose down
    Restart=always
    
    [Install]
    WantedBy=multi-user.target
    

  • Enable and start the service:

    sudo systemctl enable docker-compose-app
    sudo systemctl start docker-compose-app
    

This guide will assist your customers in setting up and managing multi-container applications using Docker Compose, making it easy to deploy and scale applications on their dedicated server.