- 127.0.0.1:3000:3000
       working_dir: /app
       volumes:
         - ./:/app
   ```

5. Finally, you need to migrate the environment variable definitions using the `environment` key.

   ```yaml
   services:
     app:
       image: node:18-alpine
       command: sh -c "yarn install && yarn run dev"
       ports:
         - 127.0.0.1:3000:3000
       working_dir: /app
       volumes:
         - ./:/app
       environment:
         MYSQL_HOST: mysql
         MYSQL_USER: root
         MYSQL_PASSWORD: secret
         MYSQL_DB: todos
   ```

### Define the MySQL service

Now, it's time to define the MySQL service. The command that you used for that container was the following:

```console
$ docker run -d \
  --network todo-app --network-alias mysql \
  -v todo-mysql-data:/var/lib/mysql \
  -e MYSQL_ROOT_PASSWORD=secret \
  -e MYSQL_DATABASE=todos \
  mysql:8.0
```

1. First define the new service and name it `mysql` so it automatically gets the network alias. Also specify the image to use as well.

   ```yaml

   services:
     app:
       # The app service definition
     mysql:
       image: mysql:8.0
   ```

2. Next, define the volume mapping. When you ran the container with `docker
   run`, Docker created the named volume automatically. However, that doesn't
   happen when running with Compose. You need to define the volume in the
   top-level `volumes:` section and then specify the mountpoint in the service
   config. By simply providing only the volume name, the default options are
   used.

   ```yaml
   services:
     app:
       # The app service definition
     mysql:
       image: mysql:8.0
       volumes:
         - todo-mysql-data:/var/lib/mysql

   volumes:
     todo-mysql-data:
   ```

3. Finally, you need to specify the environment variables.

   ```yaml
   services:
     app:
       # The app service definition
     mysql:
       image: mysql:8.0
       volumes:
         - todo-mysql-data:/var/lib/mysql
       environment:
         MYSQL_ROOT_PASSWORD: secret
         MYSQL_DATABASE: todos

   volumes:
     todo-mysql-data:
   ```

At this point, your complete `compose.yaml` should look like this:


```yaml
services:
  app:
    image: node:18-alpine
    command: sh -c "yarn install && yarn run dev"
    ports:
      - 127.0.0.1:3000:3000
    working_dir: /app
    volumes:
      - ./:/app
    environment:
      MYSQL_HOST: mysql
      MYSQL_USER: root
      MYSQL_PASSWORD: secret
      MYSQL_DB: todos

  mysql:
    image: mysql:8.0
    volumes:
      - todo-mysql-data:/var/lib/mysql
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: todos

volumes:
  todo-mysql-data:
```

## Run the application stack

Now that you have your `compose.yaml` file, you can start your application.

1. Make sure no other copies of the containers are running first. Use `docker ps` to list the containers and `docker rm -f <ids>` to remove them.

2. Start up the application stack using the `docker compose up` command. Add the
   `-d` flag to run everything in the background.

   ```console
   $ docker compose up -d
   ```

    When you run the previous command, you should see output like the following:

   ```plaintext
   Creating network "app_default" with the default driver