upstream sent too big header while reading response header from upstream
Add:
fastcgi_buffers 16 16k;
fastcgi_buffer_size 32k;
proxy_buffer_size 128k;
proxy_buffers 4 256k;
proxy_busy_buffers_size 256k;
To server{} in nginx.conf
netstat -abn or netstat -a -n -p tcp -o