>On the other hand, it looks like sending of the request is still
>in progress, and upstream server replies before the request was
>completely sent. It might indicate it just doesn't wait long
>enough, and the problem is in the backend (and slow connectivity
>to the backend).

>I don't see any pause in request sending you've claimed in your
>initial message.

>On the other hand, here is ~ 30s pause you've probably talked
>about. It might indicate that upstream tries to send headers
>before "receiving and interpreting a request message" (as per HTTP
>RFC2616 it should do it "after"), which confuses nginx and makes
>it to think further body bytes aren't needed.

>understand the real problem.


Yes, I agree and also notice where the real problem is. I just created a fake backend (which simply receives the uploaded data and writes into disk), nginx correctly pass all the data to it.

Let me hack the backend code to see what's wrong. Will update if I found something new.

Thanks for your inspired comments :)