Understanding WSGI together with Apache

[Johannes Bauer]

Hi there,

I'm running an Apache 2.4 webserver using mod_wsgi 4.3.0. There are two
different applications running in there running on two completely
separate vhosts.

I'm seeing some weird crosstalk between them which I do not understand.
In particular, crosstalk concerning the locales of the two. One
application needs to output, e.g., date information using a German
locale. It uses locale.setlocale to set its LC_ALL to de_DE.UTF-8.

Now the second application doesn't need nor want to be German. It wants
to see the C locale everywhere, in particular because at some point it
uses datetime.datetime.strptime() to parse a datetime.

Here's where things get weird: Sometimes, my "C" locale process throws
exceptions, because it's unable to parse a date. When looking why this
fails, the string looks like de_DE's "Sa, 10 Okt 2015" instead of C's
"Sat, 10 Oct 2015". This seems to happen depending on which worker
thread is currently serving the request, i.e. nondeterministically.

So all in all, this is very weird and I must admit that I don't seem to
fully understand how WSGI applications are run and served within a
mod_wsgi framework altogether. In the past it all "just worked" and I
didn't need to understand it all in-depth. But I think to be able to
debug such a weird issue, in-depth knowledge of what happens under the
hood would be helpful.

So if someone could shed some light on how it works in general or what
could cause the described issue in particular, I'd really be grateful.

Thanks,
Best regards,
Johannes

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