Hello,
if anybody is interested I've started a very small project which builds rpms using docker:

https://github.com/alanfranz/docker-rpm-builder

It's a very small wrapper around rpmbuild, and I hope it's a bit more hackable than mock (which is got plenty of functions but I find it a bit hard to understand); it's designed to work on any host that support docker ( I had some issues in using mock on host distributions that weren't either Fedora, Redhat or Centos ).

In our scenarios is already proving faster than mock, but I'm sure there's plenty of space for optimization.

If anybody is interested in contributing just drop me an email and/or submit a pull request.

bye,

Alan

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My development blog: http://ollivander.franzoni.eu
contact me at public@[mysurname].eu