[lvs-users] LVS + Xen issue

Matthias Saou thias at spam.spam.spam.spam.spam.spam.spam.egg.and.spam.freshrpms.net
Wed Aug 8 09:11:33 BST 2007

Joseph Mack NA3T wrote :

> On Tue, 7 Aug 2007, Matthias Saou wrote:
> > Hi,
> >
> > I'm setting up various Xen guests, and want to use LVS to load-balance
> > web traffic across them. I've tried two similar simple setups, and with
> > both I see the same issue where LVS doesn't work properly when the
> > director send the request to a real server on the same physical Xen
> > host.
> what happens if you have the director(s) on a separate host, 
> ie not the Xen host?

Then it works. I tried to keep it short in my initial email, but maybe
I've kept it too short. There is no problem when the director has no
real server on the same Xen host (physical machine). And it's not a web
server issue, as all Xen guests are perfect clones of each other.

For the record, the final setup I wanted was like this :

    +---------+---------+---------+---------+  Public LAN
    |         |         x         x         x
    |         |
  Xen1      Xen2      Xen3      Xen4      Xen5
  Web1+LVS1 Web2+LVS2 Web3      Web4      Web5
    |         |         |         |         |
    +---------+---------+---------+---------+  Private LAN

With Xen1 and Xen2 running two keepalived instances with VRRP for
redundancy and LVS+NAT for web load-balancing and failover, through the
Private LAN.

This setup works, expect for the issue I've outlined :
- When LVS1 is active, requests to Web1 have issues
- When LVS2 is active, requests to Web2 have issues

I'm pretty sure it's some obscure(-ish) Linux bridge or connection
tracking problem. In this particular setup, it's not that much of an
issue (5 real servers, only 4 used at a given time), so what I did was
exclude Web1 from LVS1's configuration and Web2 from LVS2's. But I'm
now setting up a similar configuration with only 3 physical servers, so
excluding one means 1/3rd less "horse power" for the cluster, which is
quite a waste.

I'm quite surprised no one has run into this before. Has anyone here
already set up LVS with Xen in some similar way and have it work?


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