version: "3.4"
networks:
    apps-net:
    db-net:
        external:
            name: db-net
services:
    web:
        image: nginx:latest
        ports:
            - "9080:80"
        volumes:
            - ./code:/code
            - ./site.conf:/etc/nginx/conf.d/default.conf

        depends_on:
            - php
        networks:
            - apps-net
            - db-net

        deploy:
            mode: replicated
            replicas: 1
    php:
        image: php:7-fpm
        volumes:
            - ./code:/code
        networks:
            - apps-net
            - db-net
        deploy:
            mode: replicated
            replicas: 1

version: '3.3'
networks:
    db-net:
        external:
            name: db-net

services:
    db:
        image: mysql:5.7
        volumes:
            - db_data:/var/lib/mysql
        restart: always
        environment:
            MYSQL_ROOT_PASSWORD: password
            MYSQL_DATABASE: wordpress
            MYSQL_USER: root
            MYSQL_PASSWORD: password
        networks:
            - db-net

volumes:
    db_data:

nginx and php working
Fatal error: Uncaught Error: Call to undefined function mysqli_connect() in /code/index.php:11 Stack trace: #0 {main} thrown in /code/index.php on line 11