[Web-SIG] daemon tools

[Jim Fulton]

For some time, Zope has used a daemon-management tool we wrote called  
zdaemon:

   http://www.python.org/pypi/zdaemon

Until late last year, I found this tool a bit difficult to use  
because it was essentially undocumented.  I was forced to learn  
enough to mostly document it and have gained a new appreciation of  
it. (I haven't documented its  interactive shell mode, which I don't  
use. Maybe someone will document it or maybe I'll just rip it out.)   
I considered making some enhancements to it and decided to ask if  
some folks knew about alternative tools we might use instead.  See  
the discussion at:

    http://mail.zope.org/pipermail/zope3-dev/2006-December/021353.html

Ironically, this sort of tool isn't Python specific at all, and the  
discussion highlighted some non-Python tools, notably daeomontools  
and runit, neither of which seemed as appealing as zdaemon for  
various reasons.  This discussion also noted a Python-based tool  
named suoervisor2:

   http://www.plope.com/software/supervisor2/

Which seems to be derived from zdaemon and has some interesting  
features.  I think that both zdaemon and supervisor3 do a better job  
of process management than daemontools or runit.

At the recent open-space discussion, another Python-based tool was  
mentioned whos name I don't remember.

I ended up deciding to use zdaemon for our projects because it met  
our needs very well.  I added a couple of enhancements:

- The ability to set environment variables.  This is really important  
to us as it allows us to set LD_LIBRARY_PATH. This wants to be done  
in a supervisor process. A Python program can't set LD_LIBRARY_PATH  
for itself because it is too late for it to be used by the library  
loaded.

- I finished the transcript log, making it rotatable. The zdaemon  
transcript log consumes the standard error and output of the program  
zdaemon manages, providing basic logging for applications that have  
lacking or lame logging support.  (zdaemon has allowed us to make the  
spread daemon far more manageable.)

Anyway, I share this for your consideration.  There are probably  
better tools out there than zdaemon and supervisor2, but I'm not  
aware of them. :)  I'm curious what other people have found or use.

Jim

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