Add Nova Cells documentation

Clearly not very user friendly at the moment. We probably want to
include these files as part of test.

Change-Id: Ib6ed0e68b55a98920cbaf3e8ec828901b4b9ed9f
Story: 2004291
Task: 37810

ansible/roles/kolla-ansible/tests/releasenotes/notes/add-support-for-nova-cells-8e18425b52ba06ea.yaml

+---
+features:
+  - Adds support for deploying multiple Nova Cells.

doc/source/configuration/index.rst

@@ -13,3 +13,4 @@ Configuration Guide
    kolla-ansible
    bifrost
    ironic-python-agent
+   nova-cells

doc/source/configuration/nova-cells.rst

+==========
+Nova cells
+==========
+
+In the Train release, Kolla Ansible gained full support for the Nova cells v2
+scale out feature. Whilst configuring Nova cells is documented in
+:kolla-ansible-doc:`Kolla Ansible <reference/compute/nova-cells-guide>`,
+implementing that configuration in Kayobe is documented here.
+
+In Kolla Ansible, Nova cells :kolla-ansible-doc:`are configured
+<reference/compute/nova-cells-guide#groups>` via group variables. In Kayobe,
+these group variables can be set via Kayobe configuration. For example, to
+configure ``cell0001`` the following file could be created:
+
+.. code-block:: yaml
+   :caption: ``$KAYOBE_CONFIG_PATH/kolla/inventory/group_vars/cell0001/all``
+
+   ---
+   nova_cell_name: cell0001
+   nova_cell_novncproxy_group: cell0001-vnc
+   nova_cell_conductor_group: cell0001-control
+   nova_cell_compute_group: cell0001-compute
+
+After defining the cell ``group_vars`` the Kayobe inventory can be configured.
+In Kayobe, cell controllers and cell compute hosts become part of the existing
+``controllers`` and ``compute`` Kayobe groups because typically they will need
+to be provisioned in the same way. In Kolla Ansible, to prevent non-cell
+services being mapped to cell controllers, the ``controllers`` group must be
+split into two. The inventory file should also include the cell definitions.
+The following groups and hosts files give an example of how this may be
+achieved:
+
+.. code-block:: yaml
+   :caption: ``$KAYOBE_CONFIG_PATH/inventory/groups``
+
+    # Kayobe groups inventory file. This file should generally not be modified.
+    # If declares the top-level groups and sub-groups.
+
+    ###############################################################################
+    # Seed groups.
+
+    [seed]
+    # Empty group to provide declaration of seed group.
+
+    [seed-hypervisor]
+    # Empty group to provide declaration of seed-hypervisor group.
+
+    [container-image-builders:children]
+    # Build container images on the seed by default.
+    seed
+
+    ###############################################################################
+    # Overcloud groups.
+
+    [controllers]
+    # Empty group to provide declaration of controllers group.
+
+    [network:children]
+    # Add controllers to network group by default for backwards compatibility,
+    # although they could be separate hosts.
+    top-level-controllers
+
+    [monitoring]
+    # Empty group to provide declaration of monitoring group.
+
+    [storage]
+    # Empty group to provide declaration of storage group.
+
+    [compute]
+    # Empty group to provide declaration of compute group.
+
+    # Empty group to provide declaration of top-level controllers.
+    [top-level-controllers]
+
+    [overcloud:children]
+    controllers
+    network
+    monitoring
+    storage
+    compute
+
+    ###############################################################################
+    # Docker groups.
+
+    [docker:children]
+    # Hosts in this group will have Docker installed.
+    seed
+    controllers
+    network
+    monitoring
+    storage
+    compute
+
+    [docker-registry:children]
+    # Hosts in this group will have a Docker Registry deployed. This group should
+    # generally contain only a single host, to avoid deploying multiple independent
+    # registries which may become unsynchronized.
+    seed
+
+    ###############################################################################
+    # Baremetal compute node groups.
+
+    [baremetal-compute]
+    # Empty group to provide declaration of baremetal-compute group.
+
+    ###############################################################################
+    # Networking groups.
+
+    [mgmt-switches]
+    # Empty group to provide declaration of mgmt-switches group.
+
+    [ctl-switches]
+    # Empty group to provide declaration of ctl-switches group.
+
+    [hs-switches]
+    # Empty group to provide declaration of hs-switches group.
+
+    [switches:children]
+    mgmt-switches
+    ctl-switches
+    hs-switches
+
+
+.. code-block:: yaml
+   :caption: ``$KAYOBE_CONFIG_PATH/inventory/hosts``
+
+    # Kayobe hosts inventory file. This file should be modified to define the hosts
+    # and their top-level group membership.
+
+    # This host acts as the configuration management Ansible control host. This must be
+    # localhost.
+    localhost ansible_connection=local
+
+    [seed-hypervisor]
+    # Add a seed hypervisor node here if required. This host will run a seed node
+    # Virtual Machine.
+
+    [seed]
+    operator
+
+    [controllers:children]
+    top-level-controllers
+    cell-controllers
+
+    [top-level-controllers]
+    control01
+
+    [cell-controllers:children]
+    cell01-control
+    cell02-control
+
+    [compute:children]
+    cell01-compute
+    cell02-compute
+
+    [cell01:children]
+    cell01-control
+    cell01-compute
+    cell01-vnc
+
+    [cell01-control]
+    control02
+
+    [cell01-vnc]
+    control02
+
+    [cell01-compute]
+    compute01
+
+    [cell02:children]
+    cell02-control
+    cell02-compute
+    cell02-vnc
+
+    [cell02-control]
+    control03
+
+    [cell02-vnc]
+    control03
+
+    [cell02-compute]
+    compute02
+    compute03
+
+    ##################################
+
+    [mgmt-switches]
+    # Add management network switches here if required.
+
+    [ctl-switches]
+    # Add control and provisioning switches here if required.
+
+    [hs-switches]
+    # Add high speed switches here if required.
+
+Having configured the Kayobe inventory, the Kolla Ansible inventory can be
+configured. Currently this can be done via the
+``kolla_overcloud_inventory_top_level_group_map`` variable. For example, to
+configure the two cells defined in the Kayobe inventory above, the variable
+could be set to the following:
+
+.. code-block:: yaml
+   :caption: ``$KAYOBE_CONFIG_PATH/kolla.yml``
+
+   kolla_overcloud_inventory_top_level_group_map:
+     control:
+       groups:
+         - top-level-controllers
+     network:
+       groups:
+         - network
+     compute:
+       groups:
+         - compute
+     monitoring:
+       groups:
+         - monitoring
+     cell-control:
+       groups:
+         - cell-controllers
+     cell0001:
+       groups:
+         - cell01
+     cell0001-control:
+        groups:
+         - cell01-control
+     cell0001-compute:
+       groups:
+         - cell01-compute
+     cell0001-vnc:
+       groups:
+         - cell01-vnc
+     cell0002:
+       groups:
+         - cell02
+     cell0002-control:
+       groups:
+         - cell02-control
+     cell0002-compute:
+       groups:
+         - cell02-compute
+     cell0002-vnc:
+       groups:
+         - cell02-vnc
+
+Finally, Nova cells can be enabled in Kolla Ansible:
+
+.. code-block:: yaml
+   :caption: ``$KAYOBE_CONFIG_PATH/kolla/globals.yml``
+
+    enable_cells: True