There’s a chart covering the highlights of differences between GPL and Professional (and Plesk and cPanel) here:
http://www.virtualmin.com/compare.html
It’s in the bottom menu labeled “Compare”. Eric has worked on a new comparison list that we’ll be putting on the new website in the next week or so, which covers the differences in more details.
1) seamless migration to it without reconfigure or off-time
Of course. It’s possible to go back and forth between Pro and GPL without any downtime, assuming you installed using the install.sh script (this is the only way we can be sure what the system looks like, so it’s the only way I can have any confidence that the built-in upgrade feature will work).
2) no PL*SK-like hassle with upgrades and machine changes (IP-change)
Of course. Moving to a new machine might trigger a warning about license usage on more than the licensed number of servers…but it is harmless and temporary. The message does not cause any functionality to stop working–any license violations that would result in us denying access to the software repository would require human intervention, and someone would contact you personally before taking any action to make sure we’re dealing with the problem appropriately (it could merely be a public license exposure situation and we just need to issue a new license, or similar, rather than an actual violation by the customer). We assume the best of all of our customers, and only in pretty blatant abuses do we do anything more than a polite email reminding folks of the license terms and asking if they’d like help installing new licenses on the “problem” machines. We hope we never have to alter this practice…though I have occasionally seen indications of piracy attempts and other fraudulent activity (mostly our only license abuse problem has been with people purchasing with stolen credit cards or PayPal accounts, so it’s not really a problem the license manager could ever solve, no matter how stringent).
3) no PL*SK prices ...
I think we’re dramatically more cost-effective than Plesk. But, we aren’t setting out to be the cheapest product on the market. We are building the most powerful products on the market–that is our primary focus. The underlying flexibility and power of Webmin and our Open Source heritage is our unique strength, so we’re playing to it.
4) maybe clustering, and one single master machine that controls many VM's
Clustering means so many things to everyone that it’s sort of a non-word at this point. If you search the forums for “clustering” you’ll find a lot of discussion about it, and it may give you some idea of where we currently stand, and where we’re going in the future with the problem of “clustering”, as we understand it. We’ll never be able to solve the problem of clustering your applications, though…it’s just not within our power, as it requires apps to be built to cluster, and most are not. And almost no other service on a web hosting server is slow enough to benefit from clustering (hot backup, yes, that’s probably a good feature…but many live servers with load balancing, and such, not so much).
As for the single master machine question, yeah. We have a really cool new product called VM2, currently in private beta, that’ll knock your socks off. And for mere management of Virtualmin systems, it’ll be cheap (like a couple hundred bucks). If you also need management of virtualization (like Xen, Zones, EC2, vservers), it’ll get a bit more expensive, but still quite cost effective for most folks.
5) creation of services of a virtual server on different machines, like web on the one, mail on the other, sql on a third...
There’s a FAQ about this one:
http://www.virtualmin.com/documentation/id,frequently_asked_questions/#can_i_run_each_service_on_a_different_machine
Web will never be “remote-able”, at least not in the next year, or so. But we’re always moving incrementally towards abstracting all other services out to being runnable on other machines. Everybody wants to do it a little bit differently, unfortunately, and so even in cases where we do support something (like mail on other machines), it often just makes people mad that we don’t do it the way they want it done, and they end up writing some of their own post-create scripts to do it their special way.
and i count API access via cmdline to the basic features an evolved system has to offer
We do, too. But, interestingly, Virtualmin GPL already had more API capability than either of our major competitors. So, it’s always provided more API coverage…and now it’s providing even more.