On Wed, 2010-05-12 at 13:00 +0200, Mauro Vanetti wrote:
> Hello!
> I'm testing load balancing between four nodes placed in two distinct 
> machines (2 + 2). The load balancer is on the first machine, where nodes 
> 11 and 12 are. Nodes 21 and 22 are on the second machine.
> When I reboot the second machine, the load balancer detects the error 
> and redirects all new requests to nodes 11 and 12 only, until the nodes 
> on the second machine are up again.
> This is all very good, the only problem is what happens in the critical 
> seconds. Clearly, a few sessions will fail (those already started but 
> not yet finished on nodes 21 and 22 when the second machine is 
> rebooted). When this happens, the log shows that for 1-2 seconds no 
> requests are managed (including those on the first machine!).
> This goes to the point that even if I launch an automated ping (10x a 
> second) on the first machine, the pinging is not logged during the 
> critical seconds.
> 
> Real example (requests per second logged in access_log):
> 100
> 112
> 102
> 92
> 32 <-- CRISIS
> 0 <-- PEAK OF THE CRISIS
> 3 <-- CRISIS
> 25 <-- CRISIS
> 55 <-- RECOVERY
> 98
> 93
> 101
> 
> What can be the reason for this behaviour?
> Thank you very much for your help. Best regards!

What kind of Load Balancing?
Apache wouldn't log a ping, since its not a valid HTTP request, so I
don't know what kind of logging you're talking about.

-- 
Mark Watts BSc RHCE MBCS
Senior Systems Engineer, Managed Services Manpower
www.QinetiQ.com
QinetiQ - Delivering customer-focused solutions
GPG Key: http://www.linux-corner.info/mwatts.gpg

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