auth: LUA records consistent hashing-based selector

[chbruyand]

• Program: Authoritative
• Issue type: Feature request

Short description

It would be nice to provide a consistent-hashing-based selector in the LUA records functions.

Usecase

In functions such as ifportup(), we provide multiple selectors like random or hashed for instance. hashed is very fast and convenient, but has the downside of resdistributing most of the clients if the size of the UP backends changes.

Having a new chashed selector would allow to limit the number of rebalanced clients when the list of UP backends would change.