Docker Compose

Docker Compose simplifies the management of multi-container applications. Instead of running multiple docker run commands, Compose uses a single configuration file to define and manage services.

What is Docker Compose?

Docker Compose is a tool for defining and running multi-container Docker applications. You use a YAML file to configure your application’s services, networks, and volumes — then launch them all with a single command.

Defined using a docker-compose.yml file
Supports isolated services and networking between containers
Perfect for microservices, full-stack development, and testing pipelines

Installing Docker Compose

Docker Compose is included in Docker Desktop for Windows and macOS. For Linux:

sudo apt update
sudo apt install docker-compose

Verify installation:

docker-compose --version

Writing a `docker-compose.yml` File

Below is an example configuration for a .NET Web API with a PostgreSQL database:

version: '3.8'

services:
  webapp:
    build: .
    ports:
      - "8080:80"
    depends_on:
      - db

  db:
    image: postgres:15
    environment:
      POSTGRES_USER: admin
      POSTGRES_PASSWORD: secret
      POSTGRES_DB: mydb
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:

This file defines two services — webapp and db — and creates a named volume to persist data.

Running and Managing Docker Compose

Start services:
```
docker-compose up -d
```
Stop services:
```
docker-compose down
```
View logs:
```
docker-compose logs
```
Rebuild after changes:
```
docker-compose up --build
```

Networking in Docker Compose

By default, all services in a Docker Compose file are connected to the same network, allowing them to communicate using their service names. For example, webapp can connect to db using just the hostname db.

Best Practices for Docker Compose

Use environment variables and .env files to keep secrets out of your YAML.
Use named volumes for data persistence.
Use depends_on to define service dependencies.
Use docker-compose.override.yml for local overrides without changing the base config.

Docker Compose is a powerful tool for orchestrating multi-service applications with ease. It is ideal for development, testing, and CI environments where simplicity and reproducibility matter.

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