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Re: Puzzler: Can cfengine replace make?


From: Mark . Burgess
Subject: Re: Puzzler: Can cfengine replace make?
Date: Wed, 7 Nov 2001 09:35:59 +0100 (MET)

On  6 Nov, Steve Traugott wrote:
> On Tue, Nov 06, 2001 at 11:43:10PM +0100, address@hidden wrote:
>> 
>> The difference is a subtle one, but I think it's always
>> doable because the dependencies involved in most tasks
>> are simple. Make excels at deep hierarchies, but depth is
>> usually 1 in sysadm.
> 
> Y'know, Mark, this might be a reason for my continued makefile
> (ab)use.
> 
> For the things that I do, I typically have dependency trees that are
> much deeper than 1.  For instance, the makefile we're currently using
> to drive the installation and configuration of HACMP clusters has
> depths in it as high as 8.  The histogram looks like:
> 
> targets depth
>      59       1
>      31       2
>      12       3
>       7       4
>       3       5
>       1       6
>       2       7
>       2       8
> 
> So while 50% of the targets are at a depth of 1, 23% of them are at a
> depth of 3 or greater. 
> 
> I wonder where the difference in dependency usage is coming from?  Is
> anyone else doing fully-automated cluster builds?  Something equally
> complex?
> 
> (For the purposes of this discussion, "fully automated" means turn on
> the power on a pair of bare machines, walk away, come back a couple
> hours later and you've got an HA cluster.)
> 
> Steve


ONe of the things we have been researching this year is how to
reschedule partially ordered dependencies so that they don't necessarily
have to be done in order, in order to be done !! :) It might be
sufficient to say "have everything work itself out within a few seconds".

That is an approach which fits well with the principles cfengine tries
to uphold--and involves flattening the dependency tree using a transformation.
It is not *always* possible, but it is possible in many cases. I think
at the present stage, this is still a topic of research, but some of
the problems have been solved in cfengine 2. See

http://www.cfengine.org/papers.html

"Predictable management in a randomized scheduling environment.."

Mark

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