granularity/balancing issue with a small number of client IPs

[Joseph Mack NA3T]

On Wed, 15 Nov 2006, Stefan Schmidt wrote:

> Hi there,
> i have a problem loadbalancing DNS udp/53 via LVS DR.
> Whenever i have a small number of clients, in the example below it is DNS
> realtime blackhole lists used by 10 mailservers.
> Redundancy is working fine but granularity seems to be an issue and there is
> times when i end up with something like this:
> #ipvsadm --list --rate --numeric
> UDP  1.2.3.4:53                          0     1889        0   173253        0
>  -> 10.1.53.15:53                       0        0        0       18        0
>  -> 10.1.53.9:53                        0     1889        0   173235        0

I don't know, but I thought I'd pop up and say something as 
I expect the answer isn't well known. This used to work in 
the early days.

UDP schedules by packet (or small groups of packets). The 
only thing I can think of is that the director sees all your 
clients as being the one client. However I notice your 
persistence_granularity is one machine, so that shouldn't be 
a problem. Does the persistence_granularity actually get to 
the director? (I don't know where it goes - do you see it in 
the output of ipvsadm, is it in /proc somewhere?). I 
wouldn't change the persistence_timeout till you've got it 
working. I think the UDP balancing doesn't roll over to the 
next realserver for a bit longer than your value (don't 
know, 15sec?)

>
> configuration looks like this:
> virtual_server 1.2.3.4 53 {
>        delay_loop 10
>        lb_algo wrr
>        lb_kind DR
>        protocol UDP
>        ! persistence_timeout 1
>        ! persistence_granularity 255.255.255.255
> 	real_server 10.1.53.9 53 {
> 	...
>
> Same picture if i uncomment the persistence statements.
>
> I noticed there apparently are some slewing algorythms 
> doing things like a slow start whenever i add a realserver 
> but i never stumbled over any documentation, can you give 
> me a hint on where to look for this?

It's in the HOWTO as slow start and thundering herd. I 
thought it was in the code from the early days, but 
apparently it wasn't and I was mistaken. It's been talked 
about enough now that I can't remember if it ever went in or 
not.

Joe

-- 
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
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