Docker-Compose Basics

Introduction to Docker-Compose

 

Docker-Compose is a powerful tool that allows developers and system administrators to define and manage multi-container Docker applications.It simplifies the deployment of complex environments by using a declarative YAML file to specify services, networks, and volumes.Rather than running multiple docker run commands with intricate configurations, Docker-Compose provides a streamlined approach to orchestrating containers efficiently.

Maintaining and deploying applications across different environments is made easier by using a single configuration file (docker-compose.yml), making it a crucial component in modern DevOps workflows.

 

 

 

 

Key Features of Docker-Compose

 

Docker-Compose offers a range of features that make it an essential tool for containerized applications:

    Multi-Container Management: Allows defining and running multiple interdependent containers in a single configuration file.
    Service-Oriented Architecture: Enables a microservices-based approach, where each service runs in its own isolated container.
    Networking: Automatically creates and manages networks between defined services, simplifying communication.
    Volume Management: Defines persistent storage for databases and stateful applications.
    Environment Variables Support: Helps manage different configurations for development, testing, and production environments.
    Scalability: Facilitates horizontal scaling of services when necessary.
    Logging and Debugging: Provides structured logs and debugging tools for better observability.

 

 

 

 

Installing Docker-Compose

 

Before using Docker-Compose, ensure that Docker is installed on your system. Docker-Compose is included in Docker Desktop, but for standalone installations, follow these steps:

Installing on Linux

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

Verify the installation:

    docker-compose --version

 

 

Installing on Windows and macOS

For Windows and macOS users, Docker-Compose is included in Docker Desktop. Simply download and install Docker Desktop from the official Docker website.

 

 

 

 

Writing a Basic docker-compose.yml File

 

A docker-compose.yml file defines the services, networks, and volumes for a multi-container application. Below is an example of a basic configuration for a web application using Nginx and a PostgreSQL database:

    version: '3.8'
    services:
      web:
        image: nginx:latest
        ports:
          - "80:80"
        volumes:
          - ./html:/usr/share/nginx/html
        depends_on:
          - db

      db:
        image: postgres:latest
        environment:
          POSTGRES_USER: user
          POSTGRES_PASSWORD: password
          POSTGRES_DB: app_db
        volumes:
          - pg_data:/var/lib/postgresql/data

    volumes:
      pg_data:

 

 

 

 

Running and Managing Services with Docker-Compose

 

Starting the Services

Once the docker-compose.yml file is set up, launch the application with:

    docker-compose up -d

The -d flag runs the services in detached mode (background execution).

 

Viewing Running Services

Check the status of running services with:

    docker-compose ps

 

Viewing Logs

Monitor service logs using:

    docker-compose logs -f

 

Stopping Services

To stop the services, run:

    docker-compose down

This command stops and removes all containers, networks, and volumes defined in the docker-compose.yml file.

 

 

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Other useful articles in our Blog:

    - How To Install and Use Docker on Ubuntu 22.04

    - How to Create Your Own Docker Image

    - How To Remove Docker Images, Containers, and Volumes

    - What is the VPS or VDS

 

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Defining Networks and Volumes

 

Custom Network Configuration

Docker-Compose allows defining custom networks to isolate services:

    networks:
      frontend:
      backend:

    services:
      app:
        image: myapp:latest
        networks:
          - frontend
          - backend

      db:
        image: mysql:latest
        networks:
          - backend

 

 

Persistent Data Storage with Volumes

Volumes ensure data persistence when containers are restarted:

    volumes:
      mysql_data:

    services:
      database:
        image: mysql:latest
        volumes:
          - mysql_data:/var/lib/mysql

 

 

 

 

Using Environment Variables in Docker-Compose

For better configurability, environment variables can be stored in an .env file and referenced in docker-compose.yml:

.env File:

    POSTGRES_USER=admin
    POSTGRES_PASSWORD=securepassword

docker-compose.yml:

    services:
      db:
        image: postgres:latest
        environment:
          POSTGRES_USER: ${POSTGRES_USER}
          POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}

 

 

 

Scaling Services with Docker-Compose

 

Docker-Compose supports service scaling using the --scale flag:

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

This command starts three instances of the web service, distributing traffic among them.

 

 

 

 

Best Practices for Using Docker-Compose

 

    Keep Services Stateless: Store persistent data in volumes rather than within containers.
    Use .env Files for Configuration: Avoid hardcoding credentials in docker-compose.yml.
    Leverage Named Volumes: Prevent data loss during container updates.
    Define Resource Limits: Specify memory and CPU limits to prevent resource exhaustion.
    Implement Health Checks: Use healthcheck to monitor service health.

        Example of a health check:

        services:
          db:
            image: mysql:latest
            healthcheck:
              test: ["CMD", "mysqladmin", "ping", "-h", "localhost"]
              interval: 30s
              retries: 3

 

 

 

 

Conclusion

Docker-Compose is the most effective way to manage multi-container applications. Its structured and declarative configuration approach is unparalleled. Whether you're developing a local application, deploying a microservices architecture, or running a production system, Docker-Compose will enhance your efficiency by streamlining service deployment, networking, and data persistence.

If you're a DevOps engineer, developer or system administrator looking to optimise your containerised environments, then you need to understand the basics of Docker-Compose. Follow best practices and leverage its powerful features to create scalable, maintainable and robust container-based applications.