Matthias Saou wrote : > 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.
Daniel P. Berrange (who hacks extensively on Xen over at Red Hat) suggested it might be a TCP checksum offload issue... and it was! The solution is simply to use 'ethtool -K ethX tx off' on all relevant interfaces, and it all starts working as expected. I hope this will be useful to others. I'm certainly glad to know it now :-) Matthias -- Clean custom Red Hat Linux rpm packages : http://freshrpms.net/ Fedora release 7 (Moonshine) - Linux kernel 2.6.22.1-41.fc7 Load : 0.56 0.46 0.45 _______________________________________________ LinuxVirtualServer.org mailing list - [email protected] Send requests to [EMAIL PROTECTED] or go to http://lists.graemef.net/mailman/listinfo/lvs-users
