Docker与PHP，MySQL，nginx的连接问题

Question

连接到MySQL容器时出现问题。

docker-compose.yml

version: '2'

services:
    mysql:
        image: mysql:latest
        environment:
            MYSQL_ROOT_PASSWORD: JoeyW#1999
            MYSQL_DATABASE: wiput
            MYSQL_USER: web
            MYSQL_PASSWORD: Web#1234
        volumes:
            - ./mysql:/var/lib/mysql
        networks:
            - code-network
    php:
        image: wiput1999/php:latest
        volumes:
            - ./code:/code
        networks:
            - code-network
    nginx:
        image: nginx:latest
        ports:
            - "80:80"
            - "443:443"
        volumes:
            - ./code:/code
            - ./site.conf:/etc/nginx/conf.d/default.conf
            - /etc/letsencrypt:/etc/letsencrypt
        networks:
            - code-network
networks:
    code-network:
        driver: bridge

PHP测试脚本：

<?php
$servername = "localhost";
$username = "root";
$password = "JoeyW#1999";

try {
    $conn = new PDO("mysql:host=$servername;dbname=wiput", $username, $password);
    // set the PDO error mode to exception
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    echo "Connected successfully";
    }
catch(PDOException $e)
    {
    echo "Connection failed: " . $e->getMessage();
    }
?>

这个脚本对我的回应是：

Connection failed: SQLSTATE[HY000] [2002] No such file or directory

我的代码出了什么问题？因为我觉得这应该没问题

如果有人有更好的解决方案，谢谢你的帮助。