> I'm guessing that the alternative to this tidy modern repository is a gigantic broken pile of ansible/chef/puppet that hasn't been touched in 10 years.

Not quite sure how well you looked, but there are a bunch of deployment systems for HPC, Ansible or otherwise:

* https://old.reddit.com/r/HPC/comments/1p4a3fq/what_imaging_s...

* My comment listing a bunch: https://news.ycombinator.com/item?id=46037792