[lvs-users] LVS + Xen issue

Matthias Saou thias at spam.spam.spam.spam.spam.spam.spam.egg.and.spam.freshrpms.net
Tue Aug 7 16:17:56 BST 2007


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.

Scenario 1 :
- 3 physical servers (Xen Hosts) with eth0 and eth1
- 3 web servers (Xen guests), one per host, listening only on eth1
- LVS NAT is configured using keepalived on the first Xen Host

When I make a web request to the LVS director, it works fine when it
sends it to the 2nd or 3rd web servers, but only gets about the first
12kb of the page when it sends it to the 1st web server (the only one
on the same Xen Host as LVS). For pages smaller than 12kb, no problem.

Scenario 2 :
- 3 physical servers (Xen Hosts) with eth0 and eth1
- 3 web servers (Xen guests), one per host, listening only on eth1
- 1 LVS director (Xen guest), on the first Xen Host, eth0 and eth1

The exact same problem happens.

Has anyone already seen this issue?
Here are a few more details :
- RHEL5 x86_64 with latest 2.6.18-8.1.8.el5xen kernel
- keepalived package from Fedora recompiled for RHEL5
- net.ipv4.ip_forward = 1 on the LVS director
- -A POSTROUTING -s 192.168.0.0/255.255.0.0 -o eth0 -j MASQUERADE

If I remove the "local" web server from the keepalive/LVS
configuration, it works fine, since it only sends to the real servers
on the other physical servers, but that would mean not using the first
physical server's CPU power and memory, which I don't want to be
wasting.

I'm pretty sure this has something to do with connection tracking
and/or the bridges Xen configures, but I don't know what to try to fix
the issue.

Matthias

-- 
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Fedora release 7 (Moonshine) - Linux kernel 2.6.22.1-41.fc7
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