grizzly: Support for cells in Compute (nova)

[Anne Gentle]

Gathering information about cells for documenting it after it lands:

Blueprint (likely most up-to-date): http://wiki.openstack.org/blueprint-nova-compute-cells
Etherpad (http://etherpad.openstack.org/FolsomComputeCells)
Presentation referenced there (http://comstud.com/FolsomCells.pdf)
http://comstud.com/cells.pdf

The basic architecture is:

Top level cell with API service has DB, rabbit, and the nova-cells service. API's compute_api_class is overridden to use a new class that shoves every action on an instance into the nova-cells service, telling it which cell to route the request to based on instance['cell_name']. The nova-cells service routes the request to correct cell as requested… 1 hop at a time to the nova-cells service in each child.

(Each child runs this new nova-cells service also)

If nova-cells service gets a message destined for itself, it'll call the appropriate compute_api call in the child.

DB updates are hooked in the child and pushed up to parent cells.

New instance creation is slightly different. API will create the DB entry up front… and pass the uuid and all of the same data to the nova-cells service, which will pick a cell for the instance. When it is decided to use the 'current cell' in some child, it will create the DB entry there as well… push a notification upward… and cast the message over to the host scheduler (current scheduler). And the build continues as normal from there (host is picked, and message is casted to the host, etc).

There's some code to sync instances in case of lost DB updates.. but there's improvements to make yet..

[Tom Fifield (fifieldt)]

main cells code has been added.

[Tom Fifield (fifieldt)]

A paragraph should be added in the nova description in doc/src/docbkx/common/getstart.xml

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/19060
Committed: http://github.com/openstack/openstack-manuals/commit/bbb3271e75830defefbaf3278dd99546a29fe7c4
Submitter: Jenkins
Branch: master

commit bbb3271e75830defefbaf3278dd99546a29fe7c4
Author: Lorin Hochstein <email address hidden>
Date: Sun Jan 6 10:42:20 2013 -0500

    Document Cells

    Add docs for new cells functionality.

    Functionality introduced in https://review.openstack.org/15228

    Fixes bug 1075669.

    Change-Id: I3028abcb305805230d286abe08fedffe94d9e307