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Re: [lvs-users] DNS LVS questions

To: "LinuxVirtualServer.org users mailing list." <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [lvs-users] DNS LVS questions
From: Graeme Fowler <graeme@xxxxxxxxxxx>
Date: Tue, 25 Sep 2012 09:42:40 +0100
On Sun, 2012-09-23 at 02:51 -0600, Pete Ashdown wrote:
> Thanks for the localhost addressing tip.  I've got my lvs dns in production
> now and it is cranking along.  I had to lower the udp timeout to 1 second
> from my predicted 15 because the latter was crashing the server with OOM.  

Really? How many queries/sec is your system handling?

> Even with 1 second timeout, the InActConn are piling up (it hovers around 
> 300):
> 
> Prot LocalAddress:Port Scheduler Flags
>   -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
> UDP  cns1.domain.com:domain wlc
>   -> localhost:domain             Route   12     0          282      
>   -> rec3.domain.com:domain     Route   4      0          84       
> 
> I don't understand why lvs is tracking these connections, because I presume
> with UDP they don't flow back through.  Is there a trigger to have it just
> "fire and forget" UDP after it is released to the real-IP?

Those numbers are small enough to be practically insignificant. You're
right though, in DR mode there's no record of an active connection as
the three-way-handshake (for TCP connections) doesn't traverse the
director; for UDP in any mode there's no concept of state so the only
"connection" the director ever sees is "inactive" (that is, a packet was
routed).

I'm troubled by the OOM though. That would, for most modern systems,
imply something is in error in the ipvs code - unless you're running on
a system with a relatively small amount of RAM.

Graeme


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