[load balancing] ServerIronXL - Real servers failing L4 check for no apparent reason

From: Basil Hussain (basil.hussainIZZATkodakweddings.com)
Date: Mon Jul 12 2004 - 06:18:33 EDT


Hi,

I have a strange problem that I hope someone may be able to shed some light
on.

First, let me explain my set-up. I have two physical servers being
load-balanced by a Foundry ServerIron XL. I am balancing four web sites over
both. Because of the need to do SSL on more than one web site, I have to do
IP-based virtual hosting. Therefore, I have set up a virtual network
interface (using Linux IP aliasing) for each site. So, it looks like:

server-a:
        site-a: 10.1.1.100
        site-b: 10.1.1.101
        site-c: 10.1.1.102
        site-d: 10.1.1.107
server-b:
        site-a: 10.1.1.110
        site-b: 10.1.1.111
        site-c: 10.1.1.112
        site-d: 10.1.1.117

I have eight real servers set up on the LB (one for each server/site combo),
along with four virtual servers (one for each web site). Each virtual server
is therefore bound to two real servers.

The problem I am having is that my ServerIron keeps logging errors approx.
every minute telling me that two of my real servers are failing level 4
health checks:

11-07-2004 23:59:33 ServerIron, L4 server 10.1.1.110 server-b-site-a port 80
is down
11-07-2004 23:59:35 ServerIron, L4 server 10.1.1.100 server-a-site-a port 80
is down
11-07-2004 23:59:39 ServerIron, L4 server 10.1.1.100 server-a-site-a port 80
is up
11-07-2004 23:59:39 ServerIron, L4 server 10.1.1.110 server-b-site-a port 80
is up

But, strangely, it only gives errors for site A! No problems at all with all
other sites! Also, it doesn't complain about port 443.

What possible reasons could there be for this behaviour?

Regards,

--
Basil Hussain
I.T. Systems Developer and Administrator, Kodak Weddings
basil.hussainIZZATkodakweddings.com

P.S. In case anyone asks why I have eight real servers defined, one for each server/site combination, it is because of the non-contiguous IP addresses. Otherwise, I would use the 'host-range' command...

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