I'm looking for a web host that will let me run a Haskell web application. VPS's seem attractive to me because you can run essentially anything you want. But some of the cloud hosts offer really nice scalability in terms of hard disk space and bandwidth.
Does anyone know of a host that will let me run exotic languages like Haskell but can also seamlessly scale up the hard disk space/RAM/bandwidth/CPU available to my host?
If you just want very simple hosting with CGI, NearlyFreeSpeech.net supports Haskell and some other less common languages. I personally also like their overall nonsense-free approach and sensible pricing model (pre-pay metered charges, instead of the usual model of a fixed monthly charge, oversold server capacity, and absurd overage fees).
There are a few caveats however, mainly that they don't permit standalone servers or persistent daemons, only things invoked via CGI from Apache. This might be a problem for some Haskell web app frameworks.
In theory all you need is CGI/FastCGI support. I've had some luck playing around with Happstack on a very basic Dreamhost account by following these instructions:
While non-trivial to get running, this web experiment proves that it is at the very least possible to run Happstack applications on cheap hosting providers such as Dreamhost with little more than a shell account and CGI support.
I've only tried this with toy applications, and don't know how it would scale.
Apparently, it's possible to get ghc running on Webfaction. There are also threads about it in the Webfaction support forums, and the admins/techs are quite willing to try to make it work, though it'c clearly not something they'd do out of the box.
Maybe this is obvious, but you can always use Amazon EC2. You'll have full control, and definitely meets your requirement for seamlessly scaling up.