Nginx + GoFCGIでreadv() failed (104: Connection reset by peer) while reading upstream

Nginx

upstream container-sentry { server go:9000; }
location / {                       
   proxy_set_header Host $host;    
   fastcgi_pass  container-sentry;         
   include       fastcgi_params;   
   break;                          
 }                                 

Go

listener, _ := net.Listen("tcp", ":9000")
fcgi.Serve(listener, nil)

いろいろ端折ってますが、こんなかんじで動かしてた時

readv() failed (104: Connection reset by peer) while reading upstream

とおこなれ何これ？何文句あるの？
ッて思ってたけど

location / {                       
   proxy_set_header Host $host;    
   fastcgi_pass  container-sentry; 
+   fastcgi_keep_conn on;           
   include       fastcgi_params;   
   break;                          
 }    

で、かいけつ