Node.js代码 

var express = require('express');
var app = express();
var http = require('http');
 
var server = http.createServer(app);
app.set('trust proxy', true);// 设置以后，req.ips是ip数组；如果未经过代理，则为[]. 若不设置，则req.ips恒为[]
 
app.get('/', function(req, res){
  console.log("headers = " + JSON.stringify(req.headers));// 包含了各种header，包括x-forwarded-for(如果被代理过的话)
  console.log("x-forwarded-for = " + req.header('x-forwarded-for'));// 各阶段ip的CSV, 最左侧的是原始ip
  console.log("ips = " + JSON.stringify(req.ips));// 相当于(req.header('x-forwarded-for') || '').split(',')
  console.log("remoteAddress = " + req.connection.remoteAddress);// 未发生代理时，请求的ip
  console.log("ip = " + req.ip);// 同req.connection.remoteAddress, 但是格式要好一些
  res.send('Hello World');
});
 
app.listen(3000);

Nginx配置 

server
{
  listen 4000;
  location / {
    proxy_pass //127.0.0.1:3000;    proxy_redirect off;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $host;
    client_max_body_size 10m;                                    # 允许客户端请求的最大单文件字节数
    client_body_buffer_size 128k;                                # 缓冲区代理缓冲用户端请求的最大字节数，
    proxy_connect_timeout 90;                                    # nginx跟后端服务器连接超时时间(代理连接超时)
    proxy_send_timeout 90;                                       # 后端服务器数据回传时间(代理发送超时)
    proxy_read_timeout 90;                                       # 连接成功后，后端服务器响应时间(代理接收超时)
    proxy_buffer_size 4k;                                        # 设置代理服务器（nginx）保存用户头信息的缓冲区大小
    proxy_buffers 4 32k;                                         # proxy_buffers缓冲区，网页平均在32k以下的设置
    proxy_busy_buffers_size 64k;                                 # 高负荷下缓冲大小（proxy_buffers*2）
    proxy_temp_file_write_size 64k;
  }
}

运行结果(使用Postman发送GET请求)

1. 不使用代理 

命令行输出: 

headers = {"host":"127.0.0.1:3000","connection":"keep-alive","k2":"v2","k1":"v1","cache-control":"no-cache","user-agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2687.0 Safari/537.36","postman-token":"f48d86ee-5375-6768-6f0f-7af1b51f8676","accept":"*/*","accept-encoding":"gzip, deflate, sdch","accept-language":"zh-CN,zh;q=0.8,en;q=0.6"}
x-forwarded-for = undefined
ips = []
remoteAddress = ::ffff:127.0.0.1
ip = ::ffff:127.0.0.1

2. 使用代理 

命令行输出 

headers = {"x-real-ip":"127.0.0.1","x-forwarded-for":"127.0.0.1","host":"127.0.0.1","connection":"close","k2":"v2","k1":"v1","cache-control":"no-cache","user-agent":"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2687.0 Safari/537.36","postman-token":"17c79ae7-f00f-6d5f-279a-99d295cbf7d5","accept":"*/*","accept-encoding":"gzip, deflate, sdch","accept-language":"zh-CN,zh;q=0.8,en;q=0.6"}
x-forwarded-for = 127.0.0.1
ips = ["127.0.0.1"]
remoteAddress = ::ffff:127.0.0.1
ip = 127.0.0.1

提取出来的一个工具函数

// 无需设置`app.set('trust proxy', true);`function getReqRemoteIp(req){return (req.headers['x-forwarded-for'] || '').split(',')[0] || req.ip;};

或者是：

var user_ip = req.headers['x-forwarded-for'] || req.connection.remoteAddress;

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