Update to new recommended Apache/mod_wsgi config

[qris]

We are currently using this mod_wsgi configuration as the default for new projects:

WSGIDaemonProcess {{ cookiecutter.project_name }} processes=2 threads=10

I think we should be using this instead:

WSGIDaemonProcess {{ cookiecutter.project_name }} processes=1 threads=10 maximum-requests=400 display-name='%{GROUP}' deadlock-timeout=30
WSGIApplicationGroup %{GLOBAL}

Rationale for the changes:

• processes=1: I can't see any reason to use multiple processes when we have threads enabled. Using two processes eats twice as much memory and ensures that some state is not shared between processes (e.g. cached Site objects) which requires a manual restart of Apache.
• maximum-requests=400 ensures that the WSGI daemon process is recycled regularly, freeing up any memory that it may have leaked.
• display-name='%{GROUP}' allows us to identify the WSGI process(es) in the process list, differentiating them from normal Apache processes. They will appear as (wsgi:<project_name>) instead of /usr/sbin/httpd.
• deadlock-timeout=30 enables the detection and breaking of deadlocks caused by extensions starting a long-running operation in native C code without releasing the Python GIL lock. Otherwise these will hang the whole WSGI process for a long time, perhaps forever.
• WSGIApplicationGroup %{GLOBAL} causes all Python code to run in the first Python interpreter instead of a sub-interpreter, avoiding a deadlock with native extensions.

References for these recommendations:

• http://code.google.com/p/modwsgi/wiki/ConfigurationDirectives#WSGIDaemonProcess* http://code.google.com/p/modwsgi/wiki/ApplicationIssues#Python_Simplified_GIL_State_API
• https://groups.google.com/forum/#!topic/modwsgi/sMhNfDei68M (use WSGIApplicationGroup %{GLOBAL} and deadlock-timeout=sss)
• http://trac.xapian.org/ticket/185 (use WSGIApplicationGroup %{GLOBAL})

[foobacca]

I'd agree with all these apart from maximum-requests - I removed that after it started causing issues.

I forget the details, but the note I made in commit c23d988 linked to http://stackoverflow.com/a/8131650/3189 which is by the author of mod_wsgi and recommends against using maximum-requests unless you know you have an issue. He makes a similar point here: https://groups.google.com/d/msg/modwsgi/efXYx-1t5ck/M3GF9xLTMsEJ

[foobacca]

I've added all there apart from maximum-requests - so closing this issue.