How does the `app` application connect to the `db` database?

Question

Consider the following docker-compose.yml file:
```yaml
services:
  app:
    image: my-app:latest
    environment:
      - DB_HOST=db
      - DB_PORT=5432
    ports:
      - "8080:80"
  db:
    image: postgres:latest
    ports:
      - "5432:5432"
```

Accepted Answer

Via port 5432

Accepted Answer

By host name `db`

Answer

By `localhost` address

Answer

By database IP address

Question from the Docker compose test

How does the `app` application connect to the `db` database?