Module ngx_http_proxy_module
http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_ignore_client_abort
Sets the HTTP protocol version for proxying. By default, version 1.0 is used. Version 1.1 is recommended for use with keepalive connections and NTLM authentication.
Syntax: proxy_ignore_client_abort on | off;
Default:
proxy_ignore_client_abort off;
Context: http, server, location
Determines whether the connection with a proxied server should be closed when a client closes the connection without waiting for a response.