These options are necessary to configure in nginx configuration file (by default /etc/nginx/nginx.conf) usable contexts are (http, server, location):

Changes from default value

proxy_buffer_size          128k;
proxy_buffers              4 256k;
proxy_busy_buffers_size    256k;
proxy_temp_file_write_size 256k;

504 Gateway Timeout error using Nginx as Proxy

Add these variables to nginx.conf file:

proxy_connect_timeout       3600;
proxy_send_timeout          3600;
proxy_read_timeout          3600;
send_timeout                3600;

Further links that can be usefull: