Docs: Explanation of dynamic inventory

This patch provides a common place to document the behavior of the
dynamic inventory scripts provided in tree. It is intentionally
high level, so as to be less influenced by minor changes to the
scripts.

The documentation lives in the developer docs for now, but is also
linked from the install guide as it's relevant to deployers as well.

NOTE: This cannot be backported directly to liberty, since the parameter
to dynamic_inventory.py for the configuration directory is different
(--file in liberty, --config in master)

Change-Id: Ib7e8603dd70cff1d6a29730619c023aadce7b5e1

doc/source/developer-docs/index.rst

@@ -15,4 +15,5 @@ Contents:
    extending
    contribute
    additional-roles
+   inventory
 

doc/source/developer-docs/inventory.rst

@@ -0,0 +1,104 @@
+`Home <index.html>`_ OpenStack-Ansible Developer Documentation
+
+.. _developer-inventory:
+
+OpenStack-Ansible Inventory
+===========================
+
+OpenStack-Ansible uses an included script to generate the inventory of hosts
+and containers within the environment. This script is called by Ansible
+through its `dynamic inventory functionality`_.
+
+
+Generating the Inventory
+------------------------
+
+The script that creates the inventory is located at
+``playbooks/inventory/dynamic_inventory.py``.
+
+Execution
+^^^^^^^^^
+
+When running an Ansible command (such as ``ansible``, ``ansible-playbook`` or
+``openstack-ansible``) Ansible will execute the ``dynamic_inventory.py`` script
+and use its output as inventory.
+
+The command can also be run manually as follows:
+
+.. code-block:: bash
+
+    # from the playbooks directory
+    inventory/dynamic_inventory.py --config /etc/openstack_deploy/
+
+This invocation is useful when testing changes to the dynamic inventory script.
+
+Inputs
+^^^^^^
+
+The ``dynamic_inventory.py`` script takes a single argument, ``--config``. If not
+specified, the default is ``/etc/openstack_deploy/``.
+
+.. note:: In all versions prior to Mitaka, this argument was ``--file``.
+
+Within the specified directory, the following files must be present:
+
+    * ``openstack_environment.yml``
+    * ``openstack_user_config.yml``
+
+Additionally, the configuration or environment could be spread between two
+additional directories:
+
+    * ``conf.d``
+    * ``env.d``
+
+These files are used to build a definition of the environment consumable by Ansible.
+
+Outputs
+^^^^^^^
+
+Once executed, the script will output an ``openstack_inventory.json`` file into
+the directory specified with the ``--config`` argument. This is used as the
+source of truth for repeated runs.
+
+.. note::
+    The ``openstack_inventory.json`` file is the source of truth for the
+    environment. Deleting this in a production environment means that the UUID
+    portion of container names will be regenerated, which then results in new
+    containers being created. Containers generated under the previous version
+    will no longer be recognized by Ansible, even if reachable via SSH.
+
+The same JSON structure is printed to stdout, which is consumed by Ansible as
+the inventory for the playbooks.
+
+
+Inspecting and Managing the Inventory
+-------------------------------------
+
+The file ``scripts/inventory-manage.py`` is used to produce human readable
+output based on the ``/etc/openstack_deploy/openstack_inventory.json`` file.
+
+The same script can be used to safely remove hosts from the inventory.
+
+Viewing the Inventory
+^^^^^^^^^^^^^^^^^^^^^
+
+The ``/etc/openstack_deploy/openstack_inventory.json`` file is read by default.
+An alternative file can be specified with ``--file``.
+
+A list of all hosts can be seen with the ``--list-host/-l`` argument
+
+To see a listing of hosts and containers by their group, use
+``--list-groups/-g``.
+
+To see all of the containers, use ``--list-containers/-G``.
+
+Removing a Host
+^^^^^^^^^^^^^^^
+
+A host can be removed with the ``--remove-item/-r`` parameter.
+
+Use the host's name as an argument.
+
+.. include:: navigation.txt
+..  _`dynamic inventory functionality`: http://docs.ansible.com/ansible/intro_dynamic_inventory.html
+

doc/source/install-guide/configure-initial.rst

@@ -27,6 +27,9 @@ memcache, and RabbitMQ.  There are several other host types that contain
 other types of containers and all of these are listed in
 ``openstack_user_config.yml``.
 
+For details about how the inventory is generated from the environment
+configuration, please see :ref:`developer-inventory`.
+
 Affinity
 ^^^^^^^^