DNS Round Robin For Websites

Hi, All:

Let's say I have 2 or more different webhosts that host the web pages for a particular domain. The web pages are different on each host for testing purposes.

Each of the webhosts of course has different DNS.

Is there a DNS rotation service out there that will reliably rotate visitors through the different webhosts (Scenario A)? Or rotate by time-slicing (Scenario B)

e.g.
(Scenario A)
Visitor 1 goes to webhost#1, next visitor to webhost#2 and so on, in round robin fashion, and rotating back to webhost#1.

(Scenario B, this is more sophisticated)
In addition to Scenario A, there is a timer. Let's say the time is set for 5 minutes. Let's say visitor v happens to be assigned to webhost w. Once his stay at webhost w exceeds the time limit of 5 minutes, he is automatically assigned to the next webhost in the round robin, i.e. w+1, in the round robin order. So, if he tries to refresh a page or click a link on webhost w, at a time that is beyond 5 minutes, he is directed to the next webhost in the round robbin, i.e. webhost w+1.

Any advice will be appreciated. Thanks will be given.

Round Robin would not really be the way to go for this.
I would suggest writing some sort of script to change the DNS
ever 10-20-30 minutes or so. So Group A goes to Site 1, 10 minutes pass
Group B goes to Site 2. And so-on. I have never seen a sucessful Round Robin DNS rotation.

It is not possible via updating DNS every few minutes. DNS is inherently laggy, and can take upwards of 12 hours to update across the internet. (As DNS entries are cached in multiple locations throughout the world, taking quite a while for changes to propagate.) So, updating every 1 to 10 minutes would do little to nothing except give very unreliable random DNS issues everywhere. Also, it's a system with no direct feedback, so you would have no way of knowing when users request, and so not be able to rotate on a user basis. I would recommend using the domain name main site as a portal, then redirecting via a header redirect to the sites you want them to see. It's the only way you can get user-to-user or minute-to-minute control of routing. (Without having elaborate equipment in the 10's of thousands of dollars to do advanced load balancing like Google, but I doubt that's what you're going for.)