Comment 2 for bug 1742421

Reviewed: https://review.openstack.org/532491
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=30786b892e45602d76cea63ca4ae1172fb2e063e
Submitter: Zuul
Branch: master

commit 30786b892e45602d76cea63ca4ae1172fb2e063e
Author: Liam Young <email address hidden>
Date: Wed Jan 10 11:06:37 2018 +0000

    Add exception to no-upcall note of cells doc

    The cells v2 layout documentation clearly states that there are no
    upcalls from cells back to the central API services. This mislead
    me for sometime as I could not fathom how a compute node in a cell
    was supposed to report its resource info.

    It turns out nova looks up the placement service in the keystone
    catalogue and contacts it directly which to my mind is an upcall. I
    wonder if the author of the not felt that the placement service is
    not really part of nova?

    Change-Id: If14be8b182f0af4e4e6641046fec638c07e26546
    Closes-Bug: #1742421