.. Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. You can view the license at: https://creativecommons.org/licenses/by/3.0/ =============== Watcher plugins =============== Writing a Watcher Decision Engine plugin ======================================== Watcher has an external :ref:`strategy ` plugin interface which gives anyone the ability to integrate an external :ref:`strategy ` in order to make use of placement algorithms. This section gives some guidelines on how to implement and integrate custom Stategies with Watcher. Pre-requisites -------------- Before using any strategy, you should make sure you have your Telemetry service configured so that it would provide you all the metrics you need to be able to use your strategy. Creating a new plugin --------------------- First of all you have to: - Extend the base ``BaseStrategy`` class - Implement its ``execute`` method Here is an example showing how you can write a plugin called ``DummyStrategy``: .. code-block:: python # Filepath = third-party/third_party/dummy.py # Import path = third_party.dummy class DummyStrategy(BaseStrategy): DEFAULT_NAME = "dummy" DEFAULT_DESCRIPTION = "Dummy Strategy" def __init__(self, name=DEFAULT_NAME, description=DEFAULT_DESCRIPTION): super(DummyStrategy, self).__init__(name, description) def execute(self, model): self.solution.add_change_request( Migrate(vm=my_vm, src_hypervisor=src, dest_hypervisor=dest) ) # Do some more stuff here ... return self.solution As you can see in the above example, the ``execute()`` method returns a solution as required. Please note that your strategy class will be instantiated without any parameter. Therefore, you should make sure not to make any of them required in your ``__init__`` method. Abstract Plugin Class --------------------- Here below is the abstract ``BaseStrategy`` class that every single strategy should implement: .. automodule:: watcher.decision_engine.strategy.strategies.base :noindex: .. autoclass:: BaseStrategy :members: :noindex: Add a new entry point --------------------- In order for the Watcher Decision Engine to load your new strategy, the strategy must be registered as a named entry point under the ``watcher_strategies`` entry point of your ``setup.py`` file. If you are using pbr_, this entry point should be placed in your ``setup.cfg`` file. The name you give to your entry point has to be unique. Here below is how you would proceed to register ``DummyStrategy`` using pbr_: .. code-block:: ini [entry_points] watcher_strategies = dummy = third_party.dummy:DummyStrategy To get a better understanding on how to implement a more advanced strategy, have a look at the :py:class:`BasicConsolidation` class. .. _pbr: http://docs.openstack.org/developer/pbr/ Using strategy plugins ---------------------- The Watcher Decision Engine service will automatically discover any installed plugins when it is run. If a Python package containing a custom plugin is installed within the same environment as Watcher, Watcher will automatically make that plugin available for use. At this point, the way Watcher will use your new strategy if you reference it in the ``goals`` under the ``[watcher_goals]`` section of your ``watcher.conf`` configuration file. For example, if you want to use a ``dummy`` strategy you just installed, you would have to associate it to a goal like this: .. code-block:: ini [watcher_goals] goals = BALANCE_LOAD:basic,MINIMIZE_ENERGY_CONSUMPTION:dummy You should take care when installing strategy plugins. By their very nature, there are no guarantees that utilizing them as is will be supported, as they may require a set of metrics which is not yet available within the Telemetry service. In such a case, please do make sure that you first check/configure the latter so your new strategy can be fully functional. Querying metrics ~~~~~~~~~~~~~~~~ The metrics available depend on the hypervisors that OpenStack manages on the specific implementation. You can find the metrics available per hypervisor and OpenStack release on the OpenStack site. There are different possible ways to obtain usage metrics in Watcher, you can use the default Ceilometer API or our Helper. The Helper attempted to make the Ceilometer API more reusable and easy to use. Read usage metrics using the Python binding ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You can find the information about the Ceilometer Python binding on the OpenStack `ceilometer client python API documentation `_ The first step is to authenticate against the Ceilometer service (assuming that you already imported the Ceilometer client for Python) with this call: .. code-block:: py cclient = ceilometerclient.client.get_client(VERSION, os_username=USERNAME, os_password=PASSWORD, os_tenant_name=PROJECT_NAME, os_auth_url=AUTH_URL) Using that you can now query the values for that specific metric: .. code-block:: py value_cpu = cclient.samples.list(meter_name='cpu_util', limit=10, q=query) Read usage metrics using the Watcher Cluster History Helper ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Here below is the abstract ``BaseClusterHistory`` class of the Helper. .. automodule:: watcher.metrics_engine.cluster_history.api :noindex: .. autoclass:: BaseClusterHistory :members: :noindex: The following snippet code shows how to create a Cluster History class: .. code-block:: py query_history = CeilometerClusterHistory() Using that you can now query the values for that specific metric: .. code-block:: py query_history.statistic_aggregation(resource_id=hypervisor.uuid, meter_name='compute.node.cpu.percent', period="7200", aggregate='avg' )