These settings is to tell nginx to not buffer the requests that it receives (i.e. buffering before forwarding to the upstream server) The consequence of buffering requests is that it will disable the ability to check progress during file upload because the the full uploaded file will be buffered by nginx and the upstream server is not aware of the file being uploaded.
# The nice configuration is only put these settings only on the upload url path
# (i.e. location directive)
#
proxy_request_buffering off;
# Browsers will upload files as chunks (chunk encoding), nginx will use buffering regardless
# of the proxy_request_buffering settings. Using http version 1.1 will make nginx completely
# disable request buffering
proxy_http_version 1.1;
# ###
# default 1m, ff the size in a request exceeds the configured value, the 413 error is returned.
# setting 0 to disable the check
client_max_body_size 0;