Comment 9 for bug 1716706

Reviewed: https://review.openstack.org/525511
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=43dbbf8d877124145b277129cbb8a12a7a0e7a0d
Submitter: Zuul
Branch: stable/pike

commit 43dbbf8d877124145b277129cbb8a12a7a0e7a0d
Author: Kevin_Zheng <email address hidden>
Date: Fri Oct 27 15:35:05 2017 +0800

    Mention API behavior change when over quota limit

    In
    https://blueprints.launchpad.net/nova/+spec/cells-count-resources-to-check-quota-in-api
    we introduced a new workflow of Quota checks. It is possible that
    concurrent requests can pass API layer checks, but blocked by
    conductor layer checks.

    This can actually trigger user-noticeable API behavior changes:
    As an user, previously, If my request is blocked by quota checks, I will
    get HTTP 403 response, and no instance records will be left.

    After the above mentioned change, it is possible that when my requests
    failed at conductor layer Quota check and I got an instance in ERROR
    state. And in an busy cloud, users may got a lot of ERROR instances
    according to this and the instance number may beyond the limit.

    We should at least mention this behavior change in the release note.

    Change-Id: I05606fffab4e24fc55465067b66c6a035a787d1e
    Related-Bug: #1716706
    (cherry picked from commit f49ec409fd8fe2dc38d2978255c68850c427f94a)