Comment 37 for bug 1853009

Reviewed: https://review.opendev.org/c/openstack/nova/+/811807
Committed: https://opendev.org/openstack/nova/commit/0fc104eeea065579f7fa9b52794d5151baefc84c
Submitter: "Zuul (22348)"
Branch: stable/wallaby

commit 0fc104eeea065579f7fa9b52794d5151baefc84c
Author: Mark Goddard <email address hidden>
Date: Tue Nov 19 16:51:01 2019 +0000

    Invalidate provider tree when compute node disappears

    There is a race condition in nova-compute with the ironic virt driver
    as nodes get rebalanced. It can lead to compute nodes being removed in
    the DB and not repopulated. Ultimately this prevents these nodes from
    being scheduled to.

    The issue being addressed here is that if a compute node is deleted by a
    host which thinks it is an orphan, then the resource provider for that
    node might also be deleted. The compute host that owns the node might
    not recreate the resource provider if it exists in the provider tree
    cache.

    This change fixes the issue by clearing resource providers from the
    provider tree cache for which a compute node entry does not exist. Then,
    when the available resource for the node is updated, the resource
    providers are not found in the cache and get recreated in placement.

    Change-Id: Ia53ff43e6964963cdf295604ba0fb7171389606e
    Related-Bug: #1853009
    Related-Bug: #1841481
    (cherry picked from commit 2bb4527228c8e6fa4a1fa6cfbe80e8790e4e0789)