[Twisted-web] A twisted wsgi success

[Ian Schenck]

I mostly lurk on here, but I wanted to share my recent experience switching
my company's wsgi container to twisted wsgi.

We had been using a particular wsgi container implemented in C. As time
went on problems creeped up with cython modules, segfaults happened, and
threading had to be disabled. Things that worked in development would not
work in production. At this point I wanted two things: the development
container should be the production container, and the container of choice
should provide a python interpreter environment consistent with actual
python. These containers written in C which treat your application like a
plugin fail to do that across the board.

We no longer have any of the issues we had before (cython, threading,
segfaults), and if something were to break in production, it is probably
broken in development and won't make it out the door. Development servers
run the same twisted wsgi container that runs in production, in fact they
are both launched the same (but middlewares and reloaders differ). That
consistency is a really big deal. Additionally, deployment and config
management dropped a few hundred lines.

The biggest pushback I received was over performance. We benched our real
world application (versus, ahem, just returning a string) and found our
median response time was consistently 1-2ms higher across various
concurrency levels. That's insignificant for us. Under high load, twisted
wsgi actually did better with tail latency (99%ile and max). Maybe that
slight bump in median latency is because our web workers now speak http
instead of a "light weight protocol" akin to scgi, but the benefits of
talking http (curl much?) are also worth a millisecond or two.

Thanks for all the hard work, and thanks Glyph for your 2011 Djangocon talk
and your tweets leading me to twisted wsgi. We're very happy. If anyone
wants details or a peek at some of the wiring, I can probably get approval
to share more.
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