The use of virtual machines is getting very popular in the web hosting world. Particularly exciting to many people is Amazon.com's EC2 -- which means Elastic Compute Cloud. It's a large pool of virtual machines that you can rent by the hour. I know people planning on basing whole companies on this system, because they can build an application that scales up by adding more virtual machines on demand. It's decently priced and a lot cheaper than building it yourself in most cases.

In many ways, something like EC2 would be great for all those web sites which deal with the "slashdot" effect. I hope to see web hosters, servers and web applications just naturally allow scaling through the addition of extra machines. This typically means either some round-robin-DNS, or a master server that does redirects to a pool of servers, or a master cache that processes the data from a pool of servers, or a few other methods. Dealing with persistent state that can't be kept in cookies requires a shared database among all the servers, which may make the database the limiting factor. Rumours suggest Amazon will release an SQL interface to their internal storage system which presumably is highly scalable, solving that problem.

As noted, this would be great for small to medium web sites. They can mostly run on a single server, but if they ever see a giant burst of traffic, for example by being linked to from a highly popular site, they can in minutes bring up extra servers to share the load. I've suggested this approach for the Battlestar Galactica Wiki I've been using -- normally their load is modest, but while the show is on, each week, predictably, they get such a huge load of traffic when the show actually airs that they have to lock the wiki down. They have tried to solve this the old fashioned way -- buying bigger servers -- but that's a waste when they really just need one day a week, 22 weeks a year, of high capacity.

However, I digress. What I really want to talk about is using such systems to get access to all sorts of platforms. As I've noted before, linux is a huge mishmash of platforms. There are many revisions of Ubuntu, Fedora, SuSE, Debian, Gentoo and many others out there. Not just the current release, but all the past releases, in both stable, testing and unstable branches. On top of that there are many versions of the BSD variants.