“Very interesting efforts are underway to offer completely
Linux-based server clustering solutions. These include the
open-source Linux Virtual Server, and other work being done by the
High Availability Linux Project. These projects show great promise,
and they may be the right answer for sites wishing to be close to
the bleeding edge. However, small businesses need fully supported
solutions that do not require substantial modification to their
existing, possibly heterogeneous, networks. This is the gap which
Polyserve hopes to fill with Understudy. As you will see below, I
think it does the job nicely.”
“Understudy is a software-based server clustering utility
that implements load balancing and failover protection for Linux
(Red Hat, Debian and Slackware), Solaris, Cobalt, FreeBSD and
Windows NT. It supports between two and ten heterogeneous
servers in a cluster, all of which must be located on the same DNS
subnet. Polyserve hopes to release a newer version soon that
circumvents the single subnet requirement. A cluster of servers can
provide any service, including web, mail, news or file
sharing.”
“When a server goes down, it is marked inactive within the
cluster and another server takes its place in seconds. When the
server comes back up, it is immediately reintegrated into the
cluster. By using Understudy in conjunction with a load-rotation
scheme called “round robin DNS”, a site can also provide simple
load balancing. Load balancing requires one additional IP address
for each server in the cluster. Simple failover requires only one
IP address for a “virtual host”, which is how users see the
cluster.”