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Date: Thu, 18 Aug 2011 22:00:30 -0700
From: Stephen Hansen <me+list/python@ixokai.io>
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Subject: Re: Windows service in production?
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On 8/15/11 9:32 PM, snorble wrote:
> Anyone know of a Python application running as a Windows service in
> production? I'm planning a network monitoring application that runs as
> a service and reports back to the central server. Sort of a heartbeat
> type agent to assist with "this server is down, go check on it" type
> situations.
>=20
> If using Visual Studio and C# is the more reliable way, then I'll go
> that route. I love Python, but everything I read about Python services
> seems to have workarounds ahoy for various situations (or maybe that's
> just Windows services in general?). And there seem to be multiple
> layers of workarounds, since it takes py2exe (or similar) and there
> are numerous workarounds required there, depending on which libraries
> and functionality are being used. Overall, reading about Windows
> services in Python is not exactly a confidence inspiring experience.
> If I knew of a reference example of something reliably running in
> production, I'd feel better than copying and pasting some code from a
> guy's blog.

Belatedly: I run a few quite major windows services which are installed
at various customer sites in production, and we have no issues with it
being a windows service.

I basically only ever ran into two problems:

 1. The lack of a console. Your service flat out /does not have/ a
console, which is a slightly weird state to be in: writing to sys.stdout
will fail. A print statement left in can crash things up -- even if in
third-party code.

    Now, once you realize this is there, its easy to "fix". I end up
doing something like this very early on in processing:

    class FakeFile:
        def __init__(self, fp):
            self._fp =3D fp
        def write(self, data):
            try:
                self._fp.write(data)
            except:
                pass

        # repeat with flush()

    sys.stdout =3D FakeFile(sys.stdout)
    sys.stderr =3D FakeFile(sys.stderr)

    That way it'll run from a regular terminal fine and write out fine,
but if any stray attempts to print are left in, things will pass through
fine when its running as a service.

  2. Importing modules with the same names as dlls in system32 can go
awry. I don't know if this is still there, I last touched this part of
our code a long, long, long time ago: but my service does some manual
PATH / PYTHONHOME / PYTHONPATH fiddling to take care of it. Its easy
to do.

It worked fine, and was stable and once going, everything worked fine.

Ultimately, I have since abandoned running things as a real service
directly, and wrote a "Metaservice" application we use in our company
instead. It runs as a service, and executes any random series of
programs beneath it, creating JOB's for each so any subprocesses of they
launch all get killed together cleanly, and handling dependencies via
between them through various means, and stuff like that. I just got
tired of dealing with windows stuff, so. :)

--=20

   Stephen Hansen
   ... Also: Ixokai
   ... Mail: me+list/python (AT) ixokai (DOT) io
   ... Blog: http://meh.ixokai.io/


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