Re: DNS Server Cluster

To: " users mailing list." <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: DNS Server Cluster
Cc: Horms <horms@xxxxxxxxxxxx>
Cc: Roberto Nibali <ratz@xxxxxxxxxxxx>
From: Graeme Fowler <graeme@xxxxxxxxxxx>
Date: Mon, 27 Nov 2006 20:31:09 +0000
On Mon, 2006-11-27 at 10:48 -0800, Joseph Mack NA3T wrote:
> There was a posting (in the last month I'd guess) where 
> someone's UDP balancing was not working properly and the 
> suggested solution was Julian's UDP single packet scheduler 
> patch. I forget their symptoms, but they aren't your 
> symptoms, but there may be problems with UDP we haven't 
> found because no-one is stressing UDP balancing very hard.

I know it was LVS-DR, and that it didn't have 250+ IP addresses, but the
DNS system I built for my previous employer used LVS with keepalived.
The last time I had access to the statistics, it was running at
something like 1200 queries/sec (which will have risen now by something
like 25% if memory serves), 99% of which were UDP, without a glitch.

*However* - Joe mentioned it already - I built it to balance on fwmarks,
not on TCP or UDP. Incoming packets were marked in the netfilter
'mangle' table according to protocol and port, and the LVS was then
built up from the corresponding fwmarks.

There was one network "race" we never bottomed, which has affected the
system once or twice since I left, where an unmarked packet somehow
slipped through to the "inside" (ie. realserver-facing rather than
client-facing) LAn and then caused massive traffic amplification. That
however isn't related in any way to the OP's problem.

Simon - as Joe asks, what happens with the output from ipvsadm when you
get these "hangs"? Have you tried to debug?


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