Subject: [Policy] 'config' vs. 'policy'

From: "Michael Carr" <[email-masked]>
Date: Wed, 12 Jun 2002 16:52:01 -0400

Apologize in advance if this question isn't appropriate for this list,
but not sure who/where else to ask.
 
I'm wrestling with trying to explain to developers the difference
between a 'policy' (e.g., 'if packet_type = X, put it on queue Y') and
other switch/router 'configuration' (e.g., ethernet interface 2
autosense = on).  What I have said thus far is that a policy is
something that can be expressed in an "If condition then action" clause.
Also, I've made the bold statement that static policies are part of
configuration, but not all configuration data is policy.
 
But then I hear high level "policies" in the storage networking space
like "Minimum backup count for file X is 2".  To me this is
configuration, not policy.
 
I guess I'm looking for a clearer definition.  Why does it matter?  When
trying to design and build an extensible policy engine framework (side
issue: does anyone already do this?), it helps to know the domain of the
problem set first, and optimize for that domain.  Throwing things that
aren't really policies into such an engine might lead to a
suboptimal/inefficient design with respect to the ones that really are
policies.
 
Thanks in advance
 
Michael Carr

---

From: Charles Lynn <[email-masked]>
Date: Wed, 12 Jun 2002 17:40:08 -0400 (EDT)

Michael,

Good question, no good answer that I've heard.

> configuration, not policy.

Someone said that everything is policy.
Rephrasing:
    "If ( backup_count(X) < 2 ) then replicate(X)"
    "If ( exists (ethernet.interface[2]) )
	then ethernet.interface[2].autosense = on"

(It would be more interesting if it were "Minimum backup count for any
file is 2" :-)

The fun part is deciding when to test the condition.  File creation,
deletion, *modification*; PnP interrupts; ...

Charlie

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