499s and repeated requests (1 reply)

So, I'm running a rather standard nginx -> unicorn -> rails application, all over HTTPS. Recently, I started looking into some strange load bursts (which have been going on for a while but are getting more important), and saw repeated requests (both GET and POST) in my access logs, all getting a 499 status code and reporting 0 bytes sent. I know the browser isn't seeing these 499s, but that they're closing the connection before getting data. These aren't long-running requests; I can find them in my Rails logs and they're returning in 50-100ms.

I've seen in other threads that "the user clicked save twice really fast" is the most likely cause -- but we had one client make 6500 requests over the course of a few minutes the other day, so, um, it's probably not that. I'm rather sure this isn't some kind of denial-of-service attack, either; they appear to be legit requests repeated by... the browser...? insanely quickly. I can't, alas, find any way to replicate this locally.

I know there are application-level things we can do to mitigate the effects of something like this (duplicate records being created and such), but I want to check at this end: is there some kind of configuration error I could have made that would cause this?

In case it matters, we appear to still be running nginx 1.1.19.

Thanks!
-Nate