FAQ

General

What's LVS?

LVS stands for Linux Virtual Server, which is a highly scalable and highly available server built on a cluster of real servers, with the load balancer running on the Linux operating system. Users interact as if it were a single virtual server.

Is LVS software free?

Yes! All LVS software is released under the GNU General Public License (GPL).

Is there a FreeBSD port of LVS software?

Yes, there is a FreeBSD port of IPVS, which supports the LVS/DR and LVS/TUN methods now. See the LVS On FreeBSD page for more information.

Does LVS cluster support Linux servers only?

No, real servers can almost run any operating systems in a LVS cluster, such as Linux, BSDs, Solaris, and Windows. LVS/NAT balances servers of the operating systems having TCP/IP support, LVS/TUN requires servers having IP Tunneling protocol, and LVS/DR requires servers having a non-arp device. Almost all the modern operating systems support non-arp device.

Performance

How is the concurrent processing performance of current LVS software?

The ultimate performance of LVS depends on hardware that LVS runs on. An ordinary box with a single Pentium III processor and 100Mbps NIC card running LVS/DR can handle about 10,000 connections per second for web service. We have heard that a powerful box with good hardware and kernel tuning achieved 50,000 connections per second.

Can LVS handle more than 1 million simultaneous connections?

Yes, LVS can handle much more than 1 million simultaneous connections. One connection just costs 128 bytes in the LVS box, so an LVS box with 1G memory can handle more than 8 million simultaneous connections.

Setup

How do I check to see if my kernel has IPVS enabled?

Try to run "modprobe ip_vs" and try to see if there is /proc/net/ip_vs. If so, your kernel has IPVS enabled. You can also run "cat /proc/net/ip_vs" or "ipvsadm -Ln" to see the version number of IPVS.

[root@lb4 root]# ipvsadm -Ln
IP Virtual Server version 1.0.11 (size=65536)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
...

Statistics

How do i get counters from ipvsadm in order to create graphs from?

Answer 1:

The current kernel 2.6 version of ipvsadm (v1.24) supports

ipvsadm --list --stats --numeric --exact

which gives you non-human-readable counters for Connections, Packets and Bytes for each Service Address and Realserver.

Answer 2:

Install RRDtool and preferabely Cacti onto a host of your choice. From your favorite Linux distribution, install the Net-SNMP daemon onto the Loadbalancer host. Apply the Net-SNMP-LVS-Module to the Net-SNMP daemon. Using RRDtool and/or cacti you may query the Loadbalancer and create all kind of graphs using the statistics the Loadbalancers IPVS-module delivers.