Add some inventory plugin documentation (#44727)

* Add some additional documentation about getting inventory plugins working using YAML inventory configuration files

docs/docsite/rst/plugins/inventory.rst

@@ -37,8 +37,72 @@ Using Inventory Plugins
 
 The only requirement for using an inventory plugin after it is enabled is to provide an inventory source to parse.
 Ansible will try to use the list of enabled inventory plugins, in order, against each inventory source provided.
-Once an inventory plugin succeeds at parsing a source, the any remaining inventory plugins will be skipped for that source.
+Once an inventory plugin succeeds at parsing a source, any remaining inventory plugins will be skipped for that source.
 
+To start using an inventory plugin with a YAML configuration source, create a file with the accepted filename schema for the plugin in question, then add ``plugin: plugin_name``. Each plugin documents any naming restrictions. For example, the aws_ec2 inventory plugin:
+
+.. code-block:: yaml
+
+    # demo.aws_ec2.yml
+    plugin: aws_ec2
+
+Or for the openstack plugin:
+
+.. code-block:: yaml
+
+    # clouds.yml
+    plugin: openstack
+
+The ``auto`` inventory plugin is enabled by default and works by using the ``plugin`` field to indicate the plugin that should attempt to parse it. You can configure the whitelist/precedence of inventory plugins used to parse source using the `ansible.cfg` ['inventory'] ``enable_plugins`` list. After enabling the plugin and providing any required options you can view the populated inventory with ``ansible-inventory -i demo.aws_ec2.yml --graph``::
+
+    @all:
+      |--@aws_ec2:
+      |  |--ec2-12-345-678-901.compute-1.amazonaws.com
+      |  |--ec2-98-765-432-10.compute-1.amazonaws.com
+      |--@ungrouped:
+
+You can set the default inventory path (via ``inventory`` in the `ansible.cfg` [defaults] section or the :envvar:`ANSIBLE_HOSTS` environment variable) to your inventory source(s). Now running ``ansible-inventory --graph`` should yield the same output as when you passed your YAML configuration source(s) directly. You can add custom inventory plugins to your plugin path to use in the same way.
+
+Your inventory source might be a directory of inventory configuration files. The constructed inventory plugin only operates on those hosts already in inventory, so you may want the constructed inventory configuration parsed at a particular point (such as last). Ansible parses the directory recursively, alphabetically. You cannot configure the parsing approach, so name your files to make it work predictably. Inventory plugins that extend constructed features directly can work around that restriction by adding constructed options in addition to the inventory plugin options. Otherwise, you can use ``-i`` with multiple sources to impose a specific order, e.g. ``-i demo.aws_ec2.yml -i clouds.yml -i constructed.yml``.
+
+You can create dynamic groups using host variables with the constructed ``keyed_groups`` option. The option ``groups`` can also be used to create groups and ``compose`` creates and modifies host variables. Here is an aws_ec2 example utilizing constructed features:
+
+.. code-block:: yaml
+
+    # demo.aws_ec2.yml
+    plugin: aws_ec2
+    regions:
+      - us-east-1
+      - us-east-2
+    keyed_groups:
+      # add hosts to tag_Name_value groups for each aws_ec2 host's tags.Name variable
+      - key: tags.Name
+        prefix: tag_Name_
+        separator: ""
+    groups:
+      # add hosts to the group development if any of the dictionary's keys or values is the word 'devel'
+      development: "'devel' in (tags|list)"
+    compose:
+      # set the ansible_host variable to connect with the private IP address without changing the hostname
+      ansible_host: private_ip_address
+
+Now the output of ``ansible-inventory -i demo.aws_ec2.yml --graph``::
+
+    @all:
+      |--@aws_ec2:
+      |  |--ec2-12-345-678-901.compute-1.amazonaws.com
+      |  |--ec2-98-765-432-10.compute-1.amazonaws.com
+      |  |--...
+      |--@development:
+      |  |--ec2-12-345-678-901.compute-1.amazonaws.com
+      |  |--ec2-98-765-432-10.compute-1.amazonaws.com
+      |--@tag_Name_ECS_Instance:
+      |  |--ec2-98-765-432-10.compute-1.amazonaws.com
+      |--@tag_Name_Test_Server:
+      |  |--ec2-12-345-678-901.compute-1.amazonaws.com
+      |--@ungrouped
+
+If a host does not have the variables in the configuration above (i.e. ``tags.Name``, ``tags``, ``private_ip_address``), the host will not be added to groups other than those that the inventory plugin creates and the ``ansible_host`` host variable will not be modified.
 
 .. _inventory_plugin_list: