I'm not sure I get it. Is the semantics of the JSON you store relevant to the "registry" server at all? Because if not, any JSON storage engine with a REST CRUD API should be OK, like CouchDB, etc.
You then do HTTP access control to only allow your service providing entities to add entries about themselves, and clients may only read.
Or should this "registry" actually do something with the data, like periodically actively test service availability and update reachability status? Because that sounds like a separate concern from storage and serving of the data, thus can be a separate component.