> For the complete documentation index, see [llms.txt](https://42-guide.gitbook.io/42-guide/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://42-guide.gitbook.io/42-guide/docker/compose.md).

# Compose

#### **Docker Compose Made Simple** 🚀

Docker Compose is a tool that lets you manage multi-container applications with a single command using a YAML configuration file. Let’s break it down step-by-step:

***

#### **What is Docker Compose?**

* Docker Compose simplifies the process of running **multiple containers** that work together (e.g., a web app with a database).
* You define your services (containers) in a `docker-compose.yml` file and start/stop everything with simple commands.

***

#### **How to Use Docker Compose?**

**1️⃣ Create a `docker-compose.yml` File**

This file defines all your services, networks, and volumes in one place.

Example:

```yaml
version: '3'  # Docker Compose version

services:     # Define your services (containers)
  web:        # Service name (can be anything)
    image: nginx  # Use the Nginx image
    ports:
      - "8080:80" # Map port 8080 on your machine to port 80 in the container

  db:         # Another service for the database
    image: mysql  # Use the MySQL image
    environment:  # Set environment variables for MySQL
      MYSQL_ROOT_PASSWORD: example
```

***

**2️⃣ Start All Services**

Run this command to start all services:

```bash
docker-compose up -d
```

* **`-d`**: Runs the services in detached mode (in the background).
* This will:
  * Pull the `nginx` and `mysql` images (if not already available).
  * Create containers for `web` and `db`.
  * Automatically create a network to connect the services.

***

**3️⃣ Stop All Services**

To stop and remove containers, networks, and volumes created by Docker Compose:

```bash
docker-compose down
```

***

**4️⃣ View Running Services**

Use:

```bash
docker-compose ps
```

This shows the status of your services.

***

#### **Key Features of Docker Compose**

**🛠 Environment Variables**

Store sensitive or dynamic data in an `.env` file:

```env
MYSQL_ROOT_PASSWORD=example
```

Then reference it in your `docker-compose.yml`:

```yaml
environment:
  MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
```

***

**🛠 Volumes**

You can persist data using volumes:

```yaml
services:
  db:
    image: mysql
    environment:
      MYSQL_ROOT_PASSWORD: example
    volumes:
      - dbdata:/var/lib/mysql

volumes:
  dbdata:
```

***

**🛠 Networks**

Compose automatically creates a network for all services, but you can customize it:

```yaml
services:
  web:
    image: nginx
    networks:
      - custom_network

  db:
    image: mysql
    networks:
      - custom_network

networks:
  custom_network:
```

***

#### **Commands to Know**

| Command                | Description                          |
| ---------------------- | ------------------------------------ |
| `docker-compose up`    | Start all services in the YAML file. |
| `docker-compose up -d` | Start services in detached mode.     |
| `docker-compose down`  | Stop and remove services.            |
| `docker-compose ps`    | List running services.               |
| `docker-compose logs`  | View logs for all services.          |
| `docker-compose build` | Build services from a Dockerfile.    |

***

#### **How Services Communicate**

* Containers in the same `docker-compose.yml` file can talk to each other **using their service names**.
* Example: The `web` service can connect to `db` using `db` as the hostname.

***

#### **Why Use Docker Compose?**

1. Simplifies managing multi-container apps.
2. Reproducibility: Share your `docker-compose.yml` and recreate the environment anywhere.
3. Scales easily with `docker-compose up --scale`.

***

#### **In Summary**

Docker Compose is a great tool for managing multi-container applications:

1. Define all your services in `docker-compose.yml`.
2. Start and stop everything with simple commands.
3. Use networks and volumes for communication and persistence.


---

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