This is a brief walk-through of how to create new Cisco ACI modules for Ansible.
For more information about Cisco ACI, look at the :ref:`Cisco ACI user guide <aci_guide>`.
What's covered in this section:
..contents::
:depth:3
:local:
.._aci_dev_guide_intro:
Introduction
============
Ansible already ships with a large collection of Cisco ACI modules, however the ACI object model is huge and covering all possible functionality would easily cover more than 1500 individual modules.
If you are in need of specific functionality, you have 2 options:
- Learn the ACI object model and use the low-level APIC REST API using the :ref:`aci_rest <aci_rest_module>` module
- Write your own dedicated modules, which is actually quite easy
..seealso::
`ACI Fundamentals: ACI Policy Model <https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/1-x/aci-fundamentals/b_ACI-Fundamentals/b_ACI-Fundamentals_chapter_010001.html>`_
A good introduction to the ACI object model.
`APIC Management Information Model reference <https://developer.cisco.com/docs/apic-mim-ref/>`_
Complete reference of the APIC object model.
`APIC REST API Configuration Guide <https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/2-x/rest_cfg/2_1_x/b_Cisco_APIC_REST_API_Configuration_Guide.html>`_
Detailed guide on how the APIC REST API is designed and used, incl. many examples.
So let's look at how a typical ACI module is built up.
.._aci_dev_guide_module_structure:
ACI module structure
====================
Importing objects from Python libraries
---------------------------------------
The following imports are standard across ACI modules:
The first line adds the standard connection parameters to the module. After that, the next section will update the ``argument_spec`` dictionary with module-specific parameters. The module-specific parameters should include:
The following section creates an AnsibleModule instance. The module should support check-mode, so we pass the ``argument_spec`` and ``supports_check_mode`` arguments. Since these modules support querying the APIC for all objects of the module's class, the object/parent IDs should only be required if ``state: absent`` or ``state: present``.
Once the AnsibleModule object has been initiated, the necessary parameter values should be extracted from ``params`` and any data validation should be done. Usually the only params that need to be extracted are those related to the ACI object configuration and its child configuration. If you have integer objects that you would like to validate, then the validation should be done here, and the ``ACIModule.payload()`` method will handle the string conversion.
The ACIModule class handles most of the logic for the ACI modules. The ACIModule extends functionality to the AnsibleModule object, so the module instance must be passed into the class instantiation.
..code-block:: python
aci = ACIModule(module)
The ACIModule has six main methods that are used by the modules:
The ``construct_url()`` method is used to dynamically build the appropriate URL to interact with the object, and the appropriate filter string that should be appended to the URL to filter the results.
* When the ``state`` is not ``query``, the URL is the base URL to access the APIC plus the distinguished name to access the object. The filter string will restrict the returned data to just the configuration data.
* When ``state`` is ``query``, the URL and filter string used depends on what parameters are passed to the object. This method handles the complexity so that it is easier to add new modules and so that all modules are consistent in what type of data is returned.
..note:: Our design goal is to take all ID parameters that have values, and return the most specific data possible. If you do not supply any ID parameters to the task, then all objects of the class will be returned. If your task does consist of ID parameters sed, then the data for the specific object is returned. If a partial set of ID parameters are passed, then the module will use the IDs that are passed to build the URL and filter strings appropriately.
..note:: Sometimes the APIC will require special characters ([, ], and -) or will use object metadata in the name ("vlanns" for VLAN pools); the module should handle adding special characters or joining of multiple parameters in order to keep expected inputs simple.
*``state: present`` retrieves the configuration to use as a comparison against what was entered in the task. All values that are different than the existing values will be updated.
*``state: absent`` uses the existing configuration to see if the item exists and needs to be deleted.
*``state: query`` uses this to perform the query for the task and report back the existing data.
When ``state: present``, the module needs to perform a diff against the existing configuration and the task entries. If any value needs to be updated, then the module will make a POST request with only the items that need to be updated. Some modules have children that are in a 1-to-1 relationship with another object; for these cases, the module can be used to manage the child objects.
The ``aci.payload()`` method is used to build a dictionary of the proposed object configuration. All parameters that were not provided a value in the task will be removed from the dictionary (both for the object and its children). Any parameter that does have a value will be converted to a string and added to the final dictionary object that will be used for comparison against the existing configuration.
The ``aci.payload()`` method takes two required arguments and 1 optional argument, depending on if the module manages child objects.
*``aci_class`` is the APIC name for the object's class, e.g. ``aci_class='fvBD'``
*``class_config`` is the appropriate dictionary to be used as the payload for the POST request
+ The keys should match the names used by the APIC.
+ The values should be the corresponding value in ``module.params``; these are the variables defined above
*``child_configs`` is optional, and is a list of child config dictionaries.
+ The child configs include the full child object dictionary, not just the attributes configuration portion.
If the task sets the state to absent, then the ``delete_config()`` method is all that is needed. This method does not take any arguments, and handles check mode.
To have the module exit, call the ACIModule method ``exit_json()``. This method automatically takes care of returning the common return values for you.
