TL;DR: Docker Compose simplifies multi-container application development by allowing you to define and run complex systems with a single YAML file. You create a `docker-compose.yml` file to configure services, networks, and volumes, then launch the entire stack using the `docker compose up` command.
Prerequisites
Before beginning, ensure Docker Engine and Docker Compose plugin are installed on your machine. Verify your installation by running docker --version and docker compose version in your terminal. Your system should support Linux, macOS, or Windows with WSL2 enabled.
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Step 1: Create the Project Directory
Navigate to your desired project folder using the command line. For example, type mkdir my-web-app and cd my-web-app. This directory will contain all configuration files and source code for your application. Keeping everything in one place ensures Docker Compose can easily locate dependencies and mount volumes correctly.
Step 2: Define the Compose File
Create a new file named docker-compose.yml. This file uses YAML syntax to define your services. Start with the version key, though recent versions of Docker Compose no longer strictly require it. Define your first service, such as a web frontend, by adding a services block. Specify the image to use, such as nginx:latest, and map ports using the ports key, for example, "80:80" to map host port 80 to container port 80.
Step 3: Add Additional Services
Add more services to the same YAML file. For instance, include a database service using postgres:13. Configure environment variables under the environment key for each service. Ensure that services needing to communicate use the same network. By default, Compose creates a default network, but you can define custom networks in the networks section for better control and security isolation.
Step 4: Configure Volumes
To persist data beyond container lifecycles, define volumes. Add a volumes section at the root level and reference them in specific services. For example, attach a volume to the PostgreSQL service to store database files. This prevents data loss when containers are removed or recreated. Named volumes are generally preferred over bind mounts for better performance and portability across different operating systems.
Step 5: Build and Launch
Save the YAML file and return to the terminal. Run the command docker compose up. If you want to run in detached mode, add the -d flag. Docker will download necessary images, create networks, and start containers. Watch the logs to ensure all services start without errors. If a service fails to start, check the logs with docker compose logs to identify configuration mistakes.
Step 6: Manage the Stack
To stop the application, press Ctrl+C if running in the foreground, or use docker compose down in a separate terminal. This command stops and removes containers, networks, and images if specified. To restart services without removing volumes, use docker compose restart. To rebuild images after changing Dockerfiles, use docker compose up --build.
Pro Tips
Use depends_on to define startup order, but remember it does not guarantee readiness. For complex applications, split your Compose file using extends or multiple files with -f flags. Always validate your YAML syntax using online validators or docker compose config to catch errors before deployment.
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