Docker Compose中Nginx搭配php-fpm时，为何容器命名为app才正常？

正常运行的Docker Compose配置 #

version: '3'

services:
    app:
        image: php:8.2-fpm
        working_dir: "/var/www"
        volumes:
            - ./src:/var/www/html   
        networks:
            - internal
    nginx:
        restart: always
        image: nginx:latest
        ports:
            - "8080:80"
        volumes:
            - ./nginx:/etc/nginx/conf.d
            - ./src:/var/www/html
        depends_on:
            - app
        networks:
            - internal

networks:
    internal:
        name: internal

正常运行结果 #

$ docker-compose up -d        
[+] Running 3/3
 ✔ Network internal          Created 0.1s 
 ✔ Container my-php-app-1    Started 0.5s 
 ✔ Container my-php-nginx-1  Started
   
$ curl "http://localhost:8080"
{"message": "Hello World!"}

修改后的Docker Compose配置（出现问题） #

将PHP-FPM服务名称从app改为apiapp后：

services:
    apiapp:
        image: php:8.2-fpm
        working_dir: "/var/www"
        volumes:
            - ./src:/var/www/html   
        networks:
            - internal
    nginx:
        restart: always
        image: nginx:latest
        ports:
            - "8080:80"
        volumes:
            - ./nginx:/etc/nginx/conf.d
            - ./src:/var/www/html
        depends_on:
            - apiapp
        networks:
            - internal

networks:
    internal:
        name: internal

修改后的运行结果（错误） #

$ docker-compose up -d
[+] Running 3/3
 ✔ Network internal           Created 0.0s 
 ✔ Container my-php-apiapp-1  Started 0.5s 
 ✔ Container my-php-nginx-1   Started 0.9s 
$ curl "http://localhost:8080"
curl: (52) Empty reply from server

已确认旧服务已完全移除，新旧容器无关联，但修改服务名称后服务无法正常运行。

我的Nginx配置 #

server {
    listen 80;
    root /var/www/html;
    index index.php;

    location ~ [^/]\.php(/|$) {
        fastcgi_split_path_info ^(.+?\.php)(/.*)$;
        if (!-f $document_root$fastcgi_script_name) {
            return 404;
        }
        fastcgi_param HTTP_PROXY "";
        fastcgi_pass app:9000; 
        fastcgi_index index.php;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }

    location / {
        root /var/www/html;
        index index.php;
        try_files $uri $uri/ $uri.php /index.php?$query_string =404;
    }
}

问题原因及解决方案 #

问题出在Nginx配置的fastcgi_pass app:9000;这一行：
Docker Compose中，服务名称会作为容器在内部网络中的主机名。当你把PHP-FPM服务名称从app改成apiapp后，Nginx仍然尝试通过旧的主机名app访问PHP-FPM容器，导致连接失败，返回空响应。

只需将Nginx配置中的fastcgi_pass app:9000;修改为fastcgi_pass apiapp:9000;，重新启动Nginx容器即可恢复正常。

内容的提问来源于stack exchange，提问作者iigmir