Unable to POST attachments greater than 800MB

Summary

Uploading attachments larger than 800MB via REST API fails with 504 GATEWAY_TIMEOUT HTTP on the client side and with a 499 HTTP on Nginx side.

From the tests we've done so far, we were also able to reproduce the issue when uploading attachments from 164MB up to 328MB. However, these attachments were uploaded successfully regardless of the response received.

Attachments up to 82MB were uploaded correctly and a proper 200 HTTP was received.

Example logs for Nginx:

time	src_ip	status	request_size	request_time	request_method	uri_path	http_referer	http_user_agent
2017-11-13T20:23:31Z	10.106.82.122	499	1614010186	319.165	POST	/rest/api/2/issue/ABC-51802/attachments		python-requests/2.17.3

Steps to Reproduce

1. POST a large attachment via API endpoint /rest/api/2/issue/<issue_key>attachments.
2. Watch the response code

Expected Results

If there is a limitation in content length, a proper response should be sent clarifying why the request failed. Additionally, a 499 Nginx code suggested the connection closed on the client-side, when in truth it seems to be closed by our ELB.

Actual Results

Client receives a 504 GATEWAY_TIMEOUT and Nginx shows a 499.