Mailing List Archive: mod_backhand: Wackamole

Wackamole - high availability / crash definition

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kaveh at arkasoft

Mar 2, 2004, 1:03 PM

Post #1 of 2 (1005 views)
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Wackamole - high availability / crash definition

Hi All,

I've read the FAQ and the docs but still had some
questions which I hope someone can help me with. We are in
the process of evaluating various solutions for providing a
highly available load ballanced web application.

From what I understand Wachamole will give us the
high availability part. Where for our application we will
have a cluster of servers all running our web-application
and wackamole will manage which one actually responds to
the incoming requests (kindof a live backup strategy). If
the one which is serving requests "crashes" then the wackamole
processes running on the remaining cluster memebers will promote
another server and new requests will once again be served.

The part where I have a little problem with is the
notion of "crashed" ... for example an apache web-server
which is on the wrong end of a "Denial of Service" attack will
for all intents and purposes "crash" ... but the server on which
it runs may still function minimally and send wackamole heart
beats to it's fellow cluster members and therefore appear
functional.

So my real question is what metric(s) does wackamole
use to determine if a server has crashed and can these metrics
be configured on a per application basis?

I have a few more questions ... but I guess it's best to fire them
off one at a time.

your help will be greatly appreciated.

thanks in advance,

Kaveh.

jesus at omniti

Mar 2, 2004, 2:44 PM

Post #2 of 2 (910 views)
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Wackamole - high availability / crash definition [In reply to]

On Tue, 2004-03-02 at 15:03, Kaveh Goudarzi wrote:
> So my real question is what metric(s) does wackamole
> use to determine if a server has crashed and can these metrics
> be configured on a per application basis?

wackamole doesn't use metrics. The machine is either up or down.
Wackamole uses Spread, which uses your IP network. If your IP network
goes down and "the other machines" become unavailable in that sense,
then Wackamole will do its work and take over the appropriate IP
addresses that it believes are no longer accessible.

If you want to tell wackamole that it should act differently, you can do
so with wackatrl (to tell it that is has failed) or incorporate the tiny
bits of communication that wackatrl performs into your own monitoring
program.

--
// Theo Schlossnagle
// Principal Engineer -- http://www.omniti.com/~jesus/
// Postal Engine -- http://www.postalengine.com/
// Ecelerity: fastest MTA on earth

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