使用ExpressJS，Nginx和PM2遇到502 Bad Gateway错误

Question

我正在尝试使用Nginx在Ubuntu 16上托管此Github repository。但是我收到502错误的请求错误。为了部署express js应用程序，我遵循了此Digital Ocean tutorial。我已经在主目录中克隆了仓库，并安装了pm2。我还使用pm2 start app.js启动了我的应用，并且该应用正在运行。这是我的pm2状态：

我还根据提到的Digital Ocean教程配置了Nginx代理服务器。我的配置文件（位置：/ etc / nginx / sites-available / default）如下：

# Default server configuration
#
server {
        listen 80 default_server;
        listen [::]:80 default_server;

        #root /var/www/html;
        root /home/ubuntu/blockchain-demo/routes;

        # Add index.php to the list if you are using PHP
        index index.js index.html index.htm index.nginx-debian.html;

        server_name 54.255.173.175; #this is my public IP. I don't have domain.

        location / {
                proxy_pass http://127.0.0.1:3000;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection 'upgrade';
                proxy_set_header Host $host;
                proxy_cache_bypass $http_upgrade;
        }

Nginx错误日志如下：

2018/10/15 15:38:13 [error] 6283#6283: *5 connect() failed (111: Connection refused) while connecting to upstream, client: 27.147.204.239, server: 54.255.173.175, request: "GET / HTTP/1.1", upstream: "http://127.0.0.1:3000/", host: "54.255.173.175"
2018/10/15 15:38:14 [error] 6283#6283: *5 connect() failed (111: Connection refused) while connecting to upstream, client: 27.147.204.239, server:54.255.173.175, request: "GET /favicon.ico HTTP/1.1", upstream: "http://127.0.0.1:3000/favicon.ico", host: "54.255.173.175", referrer:http://54.255.173.175/"

我用Google搜索了，找到了不同的解决方案。建议的解决方案之一是检查localhost：3000端口。这是我的本地主机端口报告：

任何人都可以帮助我找出导致错误的问题在哪里吗？提前致谢。