[lvs-users] LVS-DR Cluster Some Real Servers Stuck in SYN_RECV

Bruce Rudolph brudolph at admantx.com
Fri Feb 28 19:21:23 GMT 2014

I have an LVS-DR cluster which has been running for seven months without 
a hitch. Recently, the cluster started to timeout on the majority of 
connections. Some connections were passed through to a real server and 
processed. I have tried for a week to figure out what happened. What I 
found was that one real server out of five is connecting and servicing 
the client request. The other four real servers have the HTTP connection 
stuck in the SYN_RECV state until it times out (60 seconds).

In summary, I have seven CentOS 6.4 servers (kernel 
2.6.32-358.18.1.el6.x86_64). Two servers are configured as load 
balancers (a primary and a backup) and five real servers. I have setup 
LVS-DR using IPTables. The servers have a public IP bound to a NIC 
device and an internal VLAN bound to a second NIC. The VIP is configured 
on the real servers local loopback (lo:0)  device. The 
/etc/sysconfig/ha/lvs.cf was setup properly and everything was running 
successfully for seven months.

We installed new versions of our software for the web service we are 
running. Nothing network related. All five real servers were updated the 
same way. I am comparing the one working real server from the four that 
are not working. So far I have found nothing.

Any ideas on trouble shooting points?

Best Regards,

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