Those are quite different questions. MPI on Hadoop (if you mean using MPI from within a Hadoop application) isn't really possible at the moment, but will be soon.
MPI in a cloud environment is certainly doable - some of the folks on this list have reported using it with success on Amazon, for example. There are a few things you need to do to work thru the security firewalls, but it works okay once you do - not the best performance, but still workable.
Some of the references on this subject in our user mailing list are a bit old, but still might be useful:
On Nov 2, 2013, at 5:50 PM, basma a.azeem <basmaabdelazeem_at_[hidden]> wrote:
> can i run open mpi application on hadoop ?
> i need to test open mpi over cloud
> what other cloud alternatives i can use to test open mpi over cloud
> thank you
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