NGINX代理传递给NodeJS应用程序：返回502错误

我正在尝试将NGINX设置为我的NodeJS应用程序的前端,该应用程序在127.0.0.1:3000上运行,但我无法解决此502错误. NGINX可在本地访问,网址为http://55.55.55.5/或http：//dev.example

dev.example(文件位于：/ etc / nginx / sites-available和符号链接到启用了网站)

upstream up_dev.example {
    server 127.0.0.1:3000;
}

server {
    listen 0.0.0.0:80;
    server_name dev.example example;
    access_log /var/log/nginx/dev.example.log;

    location / {
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
      proxy_set_header Host $http_host;
      proxy_set_header X-NginX-Proxy true;

      proxy_pass http://up_dev.example/;
      proxy_redirect off;
    }
 }

error.log中

2014/09/17 19:38:26 [error] 1679#0: *1 connect() failed (111: Connection refused) while connecting to upstream,client: 55.55.55.1,server:,request: “GET / HTTP/1.1”,upstream:$