If the servers are in two separate locations, like two datacenters on either
side of the country, you are stuck with DNS-based load balancing. Like
others have mentioned, Cisco, F5 and others have products which will handle
this for you and take into account some other factors when directing
traffic. DNS load balancing works quite well, I've used the F5 BigIP and
3dns extensively, and the Foundry ServerIron (which is fairly cheap).
A little more detail into what you are trying to do would help. The most
common setup with this is to have multiple datacenters, and each datacenter
has a cluster of identical servers behind something like a BigIP. The
traffic is load balanced at that level, but your Global load balancer which
hands out DNS communicates with the local guy to figure out what the current
traffic ratio is and modifys its dns replys accordingly.
There used to be a free one for linux called Eddie, which looked quite
robust. I think it was eddieware.org or eddieware.com. There is also the
linux virtual server project, but I don't believe it has support for Global
load balancing, only local.
As a side note, I've used Cisco's CSS, F5's stuff, Alteon, and Foundry. Out
of all of them that I've used, the Foundry had the least problems and had a
nicely structured config. I would recommend the CSS, but it seems to have
quite a few bugs in the code that still need to be worked out, but the
support for SSL acceleration is nice. F5... I used to really like F5. In
fact, I was one of their beta sites back in 1999 and 2000. After some
problems with code that "broke" things, we discontinued the beta program
with them. Shortly after, their new releases were getting worse and worse,
their support seemed unwilling to help (for almost $100k a year in support,
you'd think they would care), so I switched to Foundry. An insider over at
F5 told me that most of the people who had written the original code back in
1999/2000 were all gone, and most of the problems were a result of the new
people not yet wrapping their heads around the code. This was about 2 years
ago, so it's possible they've figured out how everything is put together and
it's better now. For awhile though, it was quite bad. Feature-wise, F5 has
more features than any of the other ones, Cisco CSS comes in a somewhat
distant second place. For most people, any of the above will suffice and
most of the features available in F5 and Cisco are just nice-to-have's and
not a requirement.
-jay
