Comment 17 for bug 1773945

Reviewed: https://review.opendev.org/666438
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=1ff029c1c3792f53865c6bdb3dce8d2c51b73ca7
Submitter: Zuul
Branch: master

commit 1ff029c1c3792f53865c6bdb3dce8d2c51b73ca7
Author: Matt Riedemann <email address hidden>
Date: Wed Jun 19 16:26:07 2019 -0400

    Delete InstanceMapping in conductor if BuildRequest is already deleted

    The BuildRequest represents a server in the API until the scheduler
    picks a host in a cell and we create the instance record in that cell
    and update the instance mapping to point at the cell. If the user
    deletes the BuildRequest before the instance record is created in a
    cell, the conductor schedule_and_build_instances method cleans up the
    resource allocations created by scheduler and then continues to the
    next instance (if it's a multi-create request). The point is the instance
    does not get created in a cell, the BuildRequest is gone, and the
    instance mapping is left pointing at no cell - effectively orphaned.

    Furthermore, the archive_deleted_rows command change
    I483701a55576c245d091ff086b32081b392f746e to cleanup instance mappings
    for archived instances will not catch and cleanup the orphan instance
    mapping because there never was an instance record to delete and archive
    (the BuildRequest was deleted before the instance record was created, and
    the BuildRequest is hard deleted so there is no archive).

    This change simply deletes the InstanceMapping record in case the
    BuildRequest is already gone by the time we finish scheduling and we
    do not create the instance record in any cell.

    Change-Id: Ia03577ae41f010b449e47ff5b69b432d74f8467b
    Related-Bug: #1784074
    Related-Bug: #1773945