python wsgi behind nginx: yield not behaving as expected

Igor Sysoev igor at
Thu Nov 3 07:12:47 UTC 2011

On Thu, Nov 03, 2011 at 12:08:49AM -0700, Matt Starcrest wrote:
> Hi,
> I want to run wsgi python code on a web server behind nginx.  The server needs to respond quickly to an http request, then continue to do some (slow) work after responding.  Python's yield statement seems to fit the bill, as follows:
> def application(environ, start_response):
>     output = get_response_quickly(environ)
>     start_response('200 OK', [('Content-type', 'text/plain'), ('Content-Length', str(len(output)))])
>     yield output
>     do_slow_work()
> If I run this wsgi in a standalone python server (I tried wsgiref, fapws, uwsgi), the caller receives the output immediately (after get_response_quickly()), as desired.  Great.  However, if I run any of these servers behind nginx, the caller doesn't receive a response until *after* do_slow_work() -- thus defeating the purpose.
> Is there a way to make this pattern work with nginx?  Or is there a better way in general to respond quickly but continue work, without manually creating python threads / other clumsiness?

In nginx-1.0.9 or nginx-1.1.5 you can try
   uwsgi_buffering  off;
   sgi_buffering  off;
depending on protocol. In any modern enough nginx version you can use
    proxy_buffering off;

There is no way currently to disable buffering of FastCGI servers.

Igor Sysoev

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