Docker Compose

Docker Compose is a tool for defining and running multi-container applications. It is the key to unlocking a streamlined and efficient development and deployment experience.

Compose simplifies the control of your entire application stack, making it easy to manage services, networks, and volumes in a single YAML configuration file. Then, with a single command, you create and start all the services from your configuration file.

Commands#

Before running these commands, navigate to the folder containing your configuration/compose files.

• Start services
  • Build (if required) and start all services in foreground. 
    docker compose up
  • Start services in detached mode (recommended for normal usage). 
    docker compose up -d
  • Build specific file if multiple compose files are present in single folder. 
    docker compose -f <file-name.yml> up
     
• Stop services
  • Stop running containers without removing them. 
    docker compose stop
  • Stop and remove containers, networks, and default resources. 
    docker compose down
     
• Rebuild Service
  • Rebuild service images without starting containers. Useful when Dockerfile changes or Dependencies updated. 
    docker compose build
  • Rebuild images and starts services in one command, recommended after code or configuration changes. 
    docker compose up --build
     
• Check Service Status
  • Displays the status of all services like container name, state(up/expires), ports, etc., 
    docker compose ps
     
• View logs
  • Stream logs from all running services in real time. 
    docker compose logs -f
  • Stream logs for a specific service. 
    docker compose logs -f <service-name>
     
• Run a One-Off Command
  • Runs a temporary container to execute a command 
    docker compose run <service-name> <command>

Docker Compose File – Syntax & Components#

1. filename:

We can create separate docker compose files for different services, applications, databases, etc., 

<type-name>.docker-compose.yml 

2. version:

Specifies the compose file format version. Optional in newer Compose(v2+)

version: “3.9”

3. services:

Defines the containers that make up your application. Each key under services: represents one container.

services:
  key-name:
    image: #Specifies a pre-built image from Docker Hub or a registry.
    env_file: #used to store and inject secrets/passwords(optional).
      - .env
    build: #Builds an image from a Dockerfile instead of pulling one.(skip if pulling an image)
	    context: . #Build directory
	    dockerfile: #Custom Dockerfile name
    container_name: #Assigns a custom container name instead of auto-generated names.
    depends_on: #Controls startup order between services. Note: It does NOT wait for the service to be fully ready.
    environment: #Sets environment variables inside the container.
    ports: "HOST:CONTAINER" #Maps host machine port to container port. Used for port-forwarding
    networks: #Connects service to custom networks for inter-container communication.
    volumes: "HOST_PATH:CONTAINER_PATH" #Mounts files or directories into container. Used for persistent data
    restart: [no|always|on-failure|unless-stopped] #Defines container restart policy.
    healthcheck: #Defines container health monitoring logic.
	    test:
	    interval:
	    timeout:
	    retries:

4. volumes: 

Defines persistent volumes managed by Docker.

volumes:
  mysql_data:

5. networks:

Defines custom networks for service isolation and communication.

networks:
  backend:
    driver: bridge

Minimal Example:

When the below compose file will be run then it will create a container with database running by pull the mysql image. It will also a database with name testdb and set the username to admin and password to Root@123 using which we can connect our application to this conatainer.

services:
  app:
    image: mysql:latest
    ports:
      - "8080:8080"
    environment:
      MYSQL_DATABASE: testdb
      MYSQL_USER: admin
      MYSQL_ROOT_PASSWORD: Root@123  
      # (this is just an example, not intended to be a production configuration)
      # use .env file to inject the secrets.
    depends_on:
      - mysql

  mysql:
    image: mysql:8
    environment:
      MYSQL_ROOT_PASSWORD: root
    volumes:
      - mysql_data:/var/lib/mysql

volumes:
  mysql_data:

Conclusion#

Docker Compose simplifies the management of multi-container applications by allowing developers to define services, networks, and volumes in a single configuration file. With simple commands, entire application stacks can be built, started, stopped, and scaled efficiently, making development, testing, and deployment workflows much more streamlined.