Express(Node.js)+Nginx环境下应用无法在3000端口运行求助

我正按照教程搭建一个测试应用，相关代码如下：

app.js #

var app = require('express')();
var http = require('http').Server(app);

app.get('/', function(req, res) {
   res.sendfile('index.html');
});

http.listen(3000, function() {
   console.log('listening on *:3000');
});

index.html #

<!DOCTYPE html>
<html>
   <head>
      <title>Hello world</title>
   </head>
   <body>Hello world</body>
</html>

package.json #

{
  "name": "html",
  "version": "1.0.0",
  "description": "My project",
  "main": "app.js",
  "dependencies": {
    "express": "^4.18.2",
    "socket.io": "^4.6.2"
  },
  "devDependencies": {},
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Me",
  "license": "ISC"
}

使用nodemon app.js启动应用后，服务端运行正常，但在浏览器中访问server_ip:3000时，显示“连接尝试失败”。此前在搭载Apache的服务器上运行类似应用一切正常，怀疑问题出在Nginx上。我的操作系统为CentOS 7，以下是我的/etc/nginx/nginx.conf配置：

# For more information on configuration, see:
#   * Official English Documentation: http://nginx.org/en/docs/
#   * Official Russian Documentation: http://nginx.org/ru/docs/

user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log;
pid /run/nginx.pid;

# Load dynamic modules. See /usr/share/doc/nginx/README.dynamic.
include /usr/share/nginx/modules/*.conf;

events {
    worker_connections 1024;
}

http {
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile            on;
    tcp_nopush          on;
    tcp_nodelay         on;
    keepalive_timeout   65;
    types_hash_max_size 4096;

    include             /etc/nginx/mime.types;
    default_type        application/octet-stream;

    # Load modular configuration files from the /etc/nginx/conf.d directory.
    # See http://nginx.org/en/docs/ngx_core_module.html#include
    # for more information.
    include /etc/nginx/conf.d/*.conf;

    server {
        listen       80;
        listen       [::]:80;
        server_name  你的服务器IP;
        root         /var/www/html;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location / {
            root /var/www/html;
            index index.php index.html index.htm;
        }

        error_page 404 /404.html;
        location = /404.html {
        root /var/www/html;
        }

        error_page 500 502 503 504 /50x.html;
        location = /50x.html {
        root /var/www/html;
        }

        location ~ .php$ {          
        root /var/www/html;
        fastcgi_pass 127.0.0.1:9000;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include fastcgi_params;
        }
    }

# Settings for a TLS enabled server.
#
#    server {
#        listen       443 ssl http2;
#        listen       [::]:443 ssl http2;
#        server_name  _;
#        root         /var/www/html;
#
#        ssl_certificate "/etc/pki/nginx/server.crt";
#        ssl_certificate_key "/etc/pki/nginx/private/server.key";
#        ssl_session_cache shared:SSL:1m;
#        ssl_session_timeout  10m;
#        ssl_ciphers HIGH:!aNULL:!MD5;
#        ssl_prefer_server_ciphers on;
#
#        # Load configuration files for the default server block.
#        include /etc/nginx/default.d/*.conf;
#
#        error_page 404 /404.html;
#            location = /40x.html {
#        }
#
#        error_page 500 502 503 504 /50x.html;
#            location = /50x.html {
#        }
#    }

}

恳请告知如何解决该问题，使应用正常运行。

一、开放3000端口（直接访问用） #

如果要直接通过server_ip:3000访问应用，CentOS7默认的firewalld防火墙大概率拦截了该端口的外部请求，执行以下命令开放：

# 临时开放端口，重启服务器后失效
firewall-cmd --add-port=3000/tcp
# 永久开放端口，需重启防火墙生效
firewall-cmd --add-port=3000/tcp --permanent
firewall-cmd --reload

完成后再次尝试访问server_ip:3000，若仍无法连接，继续配置Nginx反向代理。

二、配置Nginx反向代理（推荐通过80端口访问） #

直接暴露应用端口存在安全风险，更推荐用Nginx做反向代理，通过默认的80端口访问。修改Nginx配置文件/etc/nginx/nginx.conf中的server块：

server {
    listen       80;
    listen       [::]:80;
    server_name  你的服务器IP;

    include /etc/nginx/default.d/*.conf;

    # 核心反向代理配置，将请求转发到本地3000端口的Express应用
    location / {
        proxy_pass http://127.0.0.1:3000;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }

    # 保留原有错误页配置（如果需要PHP服务，也保留对应的location规则）
    error_page 404 /404.html;
    location = /404.html {
        root /var/www/html;
    }

    error_page 500 502 503 504 /50x.html;
    location = /50x.html {
        root /var/www/html;
    }

    location ~ .php$ {          
        root /var/www/html;
        fastcgi_pass 127.0.0.1:9000;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include fastcgi_params;
    }
}

修改完成后，先验证配置合法性：

nginx -t

如果输出nginx: configuration file /etc/nginx/nginx.conf test is successful，则重启Nginx生效：

systemctl restart nginx

现在直接访问server_ip（无需加3000端口）即可看到你的Express应用。

三、额外检查项 #

• 确认Express应用监听地址：代码中http.listen(3000, ...)默认监听所有网卡（0.0.0.0），若不确定可改为http.listen(3000, '0.0.0.0', function() {...})明确指定。
• 检查应用进程状态：执行ps aux | grep node，确认nodemon或node进程正常运行。

内容的提问来源于stack exchange，提问作者Donna Lizard