[issue]How to user Reverse proxy by nginx

[wintsa123]

I used nginx for proxy, but unfortunately when I opened the page, it prompted 503

 server {
        listen 443 ssl;
        server_name pdftool.zwgczx.com;
        ssl_certificate C:/Certbot/archive/zwgczx.com/fullchain1.pem; 
        ssl_certificate_key C:/Certbot/archive/zwgczx.com/privkey1.pem;
	
        location / {
            proxy_pass http://192.168.2.227:28080;
	     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        
        
        
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
             proxy_cache hot_cache;              
             proxy_cache_valid 200 206 304 301 302 30m;              
             proxy_cache_valid any 1h;              
              proxy_cache_key $host$uri$is_args$args;              
              proxy_cache_min_uses 3;              
              proxy_cache_lock on;              
              proxy_cache_lock_timeout 3s;              
              proxy_no_cache $cookie_nocache $arg_nocache $arg_comment $arg_expression;
              add_header Cache-status $upstream_cache_status;  
	      proxy_http_version 1.1;
        }
    }