Before starting actual API development, a detailed look at compose.yaml – important for understanding deployment LATER (chapter 98).

compose.yaml in detail (shortened)

services:
    php:
        build:
            context: .
            target: frankenphp_dev
        depends_on:
            - database
        environment:
            SERVER_NAME: ${SERVER_NAME:-localhost}, php:80
            DATABASE_URL: postgresql://app:!ChangeMe!@database:5432/app?serverVersion=16&charset=utf8
            MERCURE_URL: https://php/.well-known/mercure
        volumes:
            - ./api:/app
        ports:
            - target: 443
              published: 443

    database:
        image: postgres:${POSTGRES_VERSION:-16}-alpine
        environment:
            POSTGRES_DB: ${POSTGRES_DB:-app}
            POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-!ChangeMe!}
        volumes:
            - database_data:/var/lib/postgresql/data

volumes:
    database_data:

FrankenPHP: the modern PHP application server

target: frankenphp_dev uses FrankenPHP – a modern PHP application server that combines Caddy (a web server WITH automatic HTTPS) AND the PHP interpreter in ONE process. Unlike the classic approach (Nginx/Apache PLUS a separate PHP-FPM process), EVERYTHING runs in ONE container here – simpler to operate, often more performant too.

Understanding the volumes mapping

./api:/app mirrors your LOCAL api/ directory into the container – changes to your code (edited on your machine with your editor) are IMMEDIATELY visible in the container, WITHOUT rebuilding the image. That's EXACTLY why local development stays this smooth despite Docker.

Environment variables: .env vs. compose.yaml

DATABASE_URL is set DIRECTLY in compose.yaml HERE – EXACTLY the same purpose as .env in the Symfony course (chapter 4), just defined at the Docker level instead of the PHP level. Symfony reads this environment variable EXACTLY the same way as before, regardless of WHERE it comes from.

Viewing logs

docker compose logs php --follow
docker compose logs database --follow

--follow (short: -f) streams new log lines live – invaluable for debugging, since Symfony's own var/log/ directory (chapter 4 of the Symfony course) sits INSIDE the container and isn't directly visible from the host without this command.

Logging into the container

docker compose exec php bash