..
      Copyright 2016 Mirantis Inc. All Rights Reserved.

      Licensed under the Apache License, Version 2.0 (the "License"); you may
      not use this file except in compliance with the License. You may obtain
      a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
      License for the specific language governing permissions and limitations
      under the License.

.. _plugins_runner_plugin:

Scenario runner as a plugin
===========================

Let's create a runner plugin that runs a given scenario a random number of
times (chosen at random from a given range).

Creation
^^^^^^^^

Inherit a class for your plugin from the base *ScenarioRunner* class
and implement its API (the *_run_scenario()* method):

.. code-block:: python

    import random

    from rally.task import runner
    from rally import consts


    @runner.configure(name="random_times")
    class RandomTimesScenarioRunner(runner.ScenarioRunner):
        """Sample scenario runner plugin.

        Run scenario random number of times (between min_times and max_times)
        """

        CONFIG_SCHEMA = {
            "type": "object",
            "$schema": consts.JSON_SCHEMA,
            "properties": {
                "type": {
                    "type": "string"
                },
                "min_times": {
                    "type": "integer",
                    "minimum": 1
                },
                "max_times": {
                    "type": "integer",
                    "minimum": 1
                }
            },
            "additionalProperties": True
        }

        def _run_scenario(self, cls, method_name, context, args):
            # runners settings are stored in self.config
            min_times = self.config.get('min_times', 1)
            max_times = self.config.get('max_times', 1)

            for i in range(random.randrange(min_times, max_times)):
                run_args = (i, cls, method_name,
                            runner._get_scenario_context(context), args)
                result = runner._run_scenario_once(run_args)
                # use self.send_result for result of each iteration
                self._send_result(result)

Usage
^^^^^

You can refer to your scenario runner in the input task files in the same way
as any other runners. Don't forget to put your runner-specific parameters
in the configuration as well (*"min_times"* and *"max_times"* in our example):

.. code-block:: json

    {
        "version": 2,
        "title": "Using a custom runner plugin",
        "subtasks": [
            {
                "title": "Dummy scenario with random_times runner",
                "scenario": {
                    "Dummy.dummy": {}
                },
                "runner": {
                    "random_times": {
                        "min_times": 10,
                        "max_times": 20
                    }
                },
                "contexts": {
                    "users": {
                        "tenants": 1,
                        "users_per_tenant": 1
                    }
                }
            }
        ]
    }




Different plugin samples are available
`here <https://github.com/openstack/rally/tree/master/samples/plugins>`_.
