Posts Tagged mod_wsgi

WSGI daemon mode solves python-ldap connection issues

I was porting a Django/python-ldap application to another server and getting sporadic ldap.SERVER_DOWN errors.  Some basic troubleshooting showed that the problem was occurring specifically when requests routed through mod_wsgi.  If I just ran the Python code — no problem; just the Django app via the dev server — fine; Apache straight to Django (proxying to dev server) — OK.  Now, while I had been planning to investigate mod_wsgi’s “daemon mode” for some time, I was still running all my apps in “embedded mode”.  But with this python-ldap problem, I had to dig deeper into the docs.  The mod_wsgi ApplicationIssues page discusses a number of problems related to C extension modules, and while not specifically mentioning python-ldap, it does make this generalization:

Because of the possibilty that extension module writers have not written their code to take into consideration it being used from multiple sub interpreters, the safest approach is to force all WSGI applications to run within the same application group, with that preferably being the first interpreter instance created by Python.

To force a specific WSGI application to be run within the very first Python sub interpreter created when Python is initialised, the WSGIApplicationGroup directive should be used and the group set to ‘%{GLOBAL}’.

WSGIApplicationGroup %{GLOBAL}

If it is not feasible to force all WSGI applications to run in the same interpreter, then daemon mode of mod_wsgi should be used to assign different WSGI applications to their own daemon processes. Each would then be made to run in the first Python sub interpreter instance within their respective processes.

I did try WSGIApplicationGroup %{GLOBAL} first, but (assuming I implemented it correctly), the problem remained. So I tried WSGI daemon mode and the process has proved stable.

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