SNI support in python 2.7 for Locust load tests

Reddy reddy at
Wed Oct 1 11:27:47 CEST 2014


> Reddy  writes:
> > ...
> > I'm trying to use locust ( to run load test of one site we're developing. Everything was running nice and smooth until we switch the servers to use SNI. SNI is not officially supported in python 2.7.5

> you have two options:
> Python 2.7.9 implements PEP 466 "Network Security Enhancements for
> Python 2.7.x" including TLS 1.1, 1.2 and SNI support. 2.7.9 will be
> released shortly. You could try the 2.7 branch from
> Use PyOpenSSL instead of Python's ssl module. It supports SNI, too.

> A recent post in this list regarding missing SNI support in Python 2.x
> got as a suggestion to use the "backports.ssl" package on PyPI.

Thanks Christian and Dieter for your prompt responses!
I tried yesterday with Python built from I also do use pyOpenSSL as described at so I used pip to install pyOpenSSL, ndg-httpsclient and pyasn1 as well as patched locust startup file with the following:

from urllib3.contrib import pyopenssl

I also tried adding the following:
from functools import partial
ssl.wrap_socket = partial(ssl.wrap_socket, ssl_version=ssl.PROTOCOL_TLSv1)

Finally, I've just tried with:
/usr/local/bin/pip2.7 install backports.ssl

and patching the lucust file with:

import backports.ssl as ssl
import backports.ssl.monkey as monkey
import requests

I've also added verify=False to my locust test scripts to disable certificate verification according to

...And I still get exactly the same error:

[2014-09-30 14:19:41,793] ip-x-x-x-x/ERROR/stderr: File "build/bdist.linux-x86_64/egg/OpenSSL/", line 977, in sendall
[2014-09-30 14:19:41,793] ip-x-x-x-x/ERROR/stderr: File "build/bdist.linux-x86_64/egg/OpenSSL/", line 849, in _raise_ssl_error
[2014-09-30 14:19:41,794] ip-x-x-x-x/ERROR/stderr: OpenSSL.SSL
[2014-09-30 14:19:41,794] ip-x-x-x-x/ERROR/stderr: .
[2014-09-30 14:19:41,794] ip-x-x-x-x/ERROR/stderr: WantWriteError

Now I'm starting to think it's something else than SNI, but all those scripts were working nice before and the only change done was turning on the SNI on tested servers... 

Any idea what my actually cause this WantWriteError?

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