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List:       linux-ha-dev
Subject:    re[2]: [Linux-ha-dev] "dependencies" member function for resources
From:       Greg Freemyer <freemyer () NorcrossGroup ! com>
Date:       2001-09-08 16:29:19
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 >>  Greg Freemyer wrote:
 >>
>>  > A trickier question that may be getting ahead of ourselves is:  what
 >>  about
 >>  > weighted dependencies.
 >>  > 
 >>  > For instance I have a non-Linux application I maintain that has 5
 >>  firewalls
 >>  > surrounding it.  (I know it sounds extreme, but there are multiple
 >>  extranets
 >>  > connecting into the DMZ and the security people put a firewall on each
 >>  > extranet.)  If any one of the firewalls is functioning, then a portion
 >>  of my
 >>  > user community can use the app, at least to some degree.  Therefore,
 >>  none of
 >>  > the firewalls is a true dependancy, but I would like to have the
 >>  resource
 >>  > manager move the service to whichever node has the best connectivity, or
 >>  at
 >>  > least not stop the service, just because one or two of the firewalls are
 >>  down.
 >>  > This can probably best be done by assigning different weights to each
 >>  firewalls
 >>  > IP, then have the resource manager see which node is the most
 >>  functional.  In
 >>  > my case, I know the number of users coming in via each extranet, so it
 >>  would be
 >>  > easy to set the weighting.
 >>  > 
 >>  > The current commercial cluster solution I'm using does not support
 >>  weighted
 >>  > dependencies like the above, but it would be nice.

 >>  Failsafe can do this - but it has a different paradigm.

 >>  You can write your own script to select which machine a resource runs on. 
 >>  It can use any criteria it wishes.

I hope I don't understand your last comment.

I assumed the script is just going to report what the dependencies are.  Not to 
actually test the functionality of the underlying resources. 

i.e. that would have the resource script for the above webserver calling the IP 
resource script for each of the 5 firewalls.  :(

Then, once node A's apache script new that it was 80% operation, it would have 
to communicate with node B to find out what percentage functional it was.  :(  
:(

I hope that the above status tests and IPC between nodes will be handled by the 
resource manager, not the scripts.

If so, then weighted dependencies have to be built into the resource manager, 
and that is why I brought them up.

Greg Freemyer
Internet Engineer
Deployment and Integration Specialist
The Norcross Group
www.NorcrossGroup.com

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