[RFE] Use cached copy of hash ring in api service

[Vladyslav Drok]

Currently, the API service resets the hash ring on every request, which would cause low performance in production environment. As we already cached the hash ring object, and recently introduced a way to refresh it during a interval, there could be some opportunities to reduce the db request.

[Jim Rollenhagen (jim-rollenhagen)]

Spec is here: https://review.openstack.org/#/c/250692/

[OpenStack Infra (hudson-openstack)]

Change abandoned by Zhenguo Niu (<email address hidden>) on branch: master
Review: https://review.opendev.org/250692

[Julia Kreger (juliaashleykreger)]

So, Ironic actually already does this. The challenge might be the process launch model, which could be a new process and a new copy every time. Regardless, I'm going to close this out as fixed release since it is already done, we can't account for every process launch model, and we sort of avoid the whole "who is authoritative maintainer" class of issues with a DLM or any other sort of recorder/tracker of the hash ring data/distribution.