Re: [lvs-users] ipvsadm problem

To: " users mailing list." <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [lvs-users] ipvsadm problem
From: Dmitry Akindinov <dimak@xxxxxxxxxxx>
Date: Sat, 25 Aug 2012 10:14:52 +0400

On 2012-08-24 17:14, David Coulson wrote:
> On 8/24/12 8:53 AM, Dmitry Akindinov wrote:
>> So, again, routing is fine, the traffic does go as it should (to the
>> new balancer and then to the old one, as a part of the "real server
>> pool" or "farm"). The problem is that ipvs software on the "old"
>> balancer drops some of the packets when it is running the sync daemon.
>> As soon as the sync daemon is stopped, the problem disappears.
> Sorry, I totally missed that your IPVS boxes are also your 'real'
> servers - I had an issue like that a while ago. Basically as far as I
> can tell, if there is a connection in the sync table, the kernel will
> use it even if you don't have ipvs rules entered, or even if you are
> using fwm and you don't have an applicable iptables rule.
> Someone who knows the internals of ipvs better can probably get more
> specific, but I was unable to find a workaround for it that did not
> involve disabling the sync daemon.
> On my end, I either changed my scheduler to SH and stopped using the
> sync daemon, or separated the ipvs and real servers into separate
> systems to avoid the issue altogether.

We are trying to make ipvs balancing a part of our product and would 
rather avoid requiring additional nodes for our cluster.

Actually, there is one more observation:
as soon as the a first "troubled" connection is established, the Linux 
kernel thread ksoftirqd starts to consume 100% of CPU, and as new 
connections come in, more ksoftirqd threads appear in the "top" output, 
all looping somewhere - 100% CPU utlization, till all 8 CPUs on that 
server are consumed by them.

It looks like a real bug in the ipvs software - we hav most probably to 
move this discussion to the lvs-devel list...

Best regards,
Dmitry Akindinov

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