Open Stack

Hi, I'd like you to take a look at this patch for potential
DocImpact.
https://review.openstack.org/15228

Log:
commit f9a868e86ce11f786538547c301b805bd68a1697
Author: Chris Behrens <cbehrens at codestud.com>
Date:   Fri Apr 13 05:54:48 2012 +0000

    Cells: Add the main code.
    
    This introduces *EXPERIMENTAL* compute cells functionality as a way to
    scale nova in a more distributed fashion without having to use complicated
    technologies like DB and message queue clustering.
    
    Cells are configured as a tree and the top level cell should contain
    nova-api without any nova-computes while child cells contain everything
    except nova-api.  One can think of a cell as a normal nova deployment in
    that each cell has its own DB server and message queue broker.
    
    The top level cell keeps a subset of data about ALL instances in all
    cells in its DB.  Child cells send messages to the top level cell when
    instances change state.  Data in 1 child cell is not shared with another
    child cell.
    
    A new service, nova-cells, is introduced that handles communication
    between cells and picking of a cell for new instances.  This service is
    required for every cell.  Communication between cells is pluggable with
    the only option currently implemented being communnication via RPC.
    
    Cells scheduling is separate from host scheduling.  nova-cells first picks
    a cell (currently randomly -- future patches add filtering/weighing
    functionality and decisions can be based on broadcasts of
    capacity/capabilities).  Once a cell has been selected and the new build
    request has reached its nova-cells service, it'll be sent over to the host
    scheduler in that cell and the build proceeds as it does without cells.
    
    New config options are introduced for enabling and configuring the cells
    code.  Cells is disabled by default.  All of the config options below go
    under a '[cells]' section in nova.conf.  These are the options that one
    may want to tweak:
    
    enable -- Turn on cells code (default is False)
    name -- Name of the current cell.
    capabilities -- List of arbitrary key=value pairs defining capabilities
                    of the current cell.  These are sent to parent cells,
                    but aren't used in scheduling until later filter/weight
                    support is added.
    call_timeout -- How long to wait for replies from a calls between cells
    
    When using cells, the compute API class must be changed in the API cell,
    so that requests can be proxied via nova-cells down to the correct cell
    properly.  Thus, config requirements for API cell:
    
    --
    [DEFAULT]
    compute_api_class=nova.compute.cells_api.ComputeCellsAPI.
    [cells]
    enable=True
    name=api-cell
    --
    
    Config requirements for child cell:
    
    --
    [cells]
    enable=True
    name=child-cell1
    --
    
    Another requirement is populating the 'cells' DB table in each cell.
    Each cell needs to know about its parent and children and how to
    communicate with them (message broker location, credentials, etc).
    
    Implements blueprint nova-compute-cells
    
    DocImpact
    
    Change-Id: I1b52788ea9d7753365d175abf39bdbc22ba822fe