如何调试重新启动mod_wsgi进程的apache？

Question

How can I debug apache to understand why it's restarting a mod_wsgi process? And how can this happen?

I have a django application running Apache/2.4.7 (Ubuntu) with mod_wsgi - single process, multi-threaded. I had messages in my python log file which only happen when the process first initializes - only after I manually restart apache... but apache hadn't been restarted. I didn't see anything in the apache access / error logs either. Does apache ever restart a process on it's own?

A short time later, apache basically stopped servicing any requests - as if it had hung or crashed, and I needed to restart apache.

Never seen this before - is there anything I can monitor to deep dive into the state of apache?

Relevant parts of config look like this:

###  Apache/sites-enabled/main.wsgi:
<VirtualHost 0.0.0.0:443>
    SSLEngine on
    SSLCertificateFile ...
    SSLCertificateKeyFile ...
    SSLCACertificateFile ...

    Options ExecCGI FollowSymLinks MultiViews

    AddHandler wsgi-script .wsgi
    WSGIDaemonProcess myapp
    WSGIProcessGroup myapp
    WSGIScriptAlias / /myproject/myapp.wsgi

    <Directory /myproject/scripts>
        <Files myapp.wsgi>
            Require all granted
        </Files>
    </Directory>
</VirtualHost>


####  /myproject/scripts/myapp.wsgi:
#!/usr/bin/python
import os
import sys
sys.path.append('/usr/local/lib/python2.7/site-packages')
sys.path.append('/myproject')
os.environ['DJANGO_SETTINGS_MODULE'] = 'myapp.settings'
os.environ['PYTHON_EGG_CACHE'] = '/tmp'
import django.core.handlers.wsgi
application = django.core.handlers.wsgi.WSGIHandler()

In addition to the custom initialization log entries indicating the process restarted, I noticed the following in the apache-error.log:

[Mon Sep 15 17:43:35 2014] [core:error] [pid 2801:tid 140079485876000] [client 111.111.111.111:64444] End of script output before headers: myapp.wsgi, referer: https://mysite.com/login.html

Answer 1

Set Apache LogLevel to 'info':

LogLevel info

This will cause mod_wsgi to output more messages about the restart of daemon processes.

Provide the log messages for that.

Also ensure that nothing is running in embedded mode by mistake.

WSGIRestrictEmbedded On

If your application is hanging, then the issue may be that you are using Python modules that do not work in Python sub interpreters. To combat that, set:

WSGIApplicationGroup %{GLOBAL}

For details about this see:

• http://code.google.com/p/modwsgi/wiki/ApplicationIssues#Python_Simplified_GIL_State_API

You might also watch:

• http://lanyrd.com/2013/pycon/scdyzk/

It explains a lot about how Apache can restart processes if using embedded mode and the problems that can cause.