Make service all-cells min version helper use scatter-gather

[Surya Seetharaman]

Currently the "get_minimum_version_all_cells" function in service runs sequentially and this affects the performance in case of large deployments (running a lot of cells) : https://github.com/openstack/nova/blob/stable/pike/nova/objects/service.py#L440

So it would be nice to use the scatter_gather_all_cells function to do this operation in parallel.

Also apart from the performance scaling point of view, in case connection to a particular cell fails, it would be nice to have sentinels returned which is done by the scatter_gather_all_cells. This helps when a cell is down.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/539590
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=5fe3a01b604c29b0961d19b44a873cca78891381
Submitter: Zuul
Branch: master

commit 5fe3a01b604c29b0961d19b44a873cca78891381
Author: Dan Smith <email address hidden>
Date: Wed Jan 31 08:13:36 2018 -0800

    Make service all-cells min version helper use scatter-gather

    This makes the Service get_minimum_version_all_cells() helper use the parallel
    scatter-gather utilities to make the determination. It also adds fault handling
    for cases where a cell fails to respond, and an option to ignore or raise in
    that situation.

    Closes-Bug: #1746558
    Change-Id: I62dc1033437f91bded28a9fd58759d2dbd7e55fb

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 18.0.0.0b2 development milestone.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/queens
Review: https://review.openstack.org/637594

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/637594
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=b7237a9e6c9567f2f2b8753be1cdc274951a9451
Submitter: Zuul
Branch: stable/queens

commit b7237a9e6c9567f2f2b8753be1cdc274951a9451
Author: Dan Smith <email address hidden>
Date: Wed Jan 31 08:13:36 2018 -0800

    Make service all-cells min version helper use scatter-gather

    This makes the Service get_minimum_version_all_cells() helper use the parallel
    scatter-gather utilities to make the determination. It also adds fault handling
    for cases where a cell fails to respond, and an option to ignore or raise in
    that situation.

    Closes-Bug: #1746558
    Change-Id: I62dc1033437f91bded28a9fd58759d2dbd7e55fb
    (cherry picked from commit 5fe3a01b604c29b0961d19b44a873cca78891381)

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 17.0.10 release.