def _invoke_action(
        self, action_db, runnertype_db, params, context=None, additional_contexts=None
    ):
        """
        Schedule an action execution.

        :type action_exec_spec: :class:`ActionExecutionSpecDB`

        :param params: Partially rendered parameters to execute the action with.
        :type params: ``dict``

        :rtype: :class:`LiveActionDB` on successful scheduling, None otherwise.
        """
        action_ref = action_db.ref
        runnertype_db = action_utils.get_runnertype_by_name(
            action_db.runner_type["name"]
        )

        liveaction_db = LiveActionDB(
            action=action_ref, context=context, parameters=params
        )

        try:
            liveaction_db.parameters = self.get_resolved_parameters(
                runnertype_db=runnertype_db,
                action_db=action_db,
                params=liveaction_db.parameters,
                context=liveaction_db.context,
                additional_contexts=additional_contexts,
            )
        except param_exc.ParamException as e:
            # We still need to create a request, so liveaction_db is assigned an ID
            liveaction_db, execution_db = action_service.create_request(liveaction_db)

            # By this point the execution is already in the DB therefore need to mark it failed.
            _, e, tb = sys.exc_info()
            action_service.update_status(
                liveaction=liveaction_db,
                new_status=action_constants.LIVEACTION_STATUS_FAILED,
                result={
                    "error": six.text_type(e),
                    "traceback": "".join(traceback.format_tb(tb, 20)),
                },
            )

            # Might be a good idea to return the actual ActionExecution rather than bubble up
            # the exception.
            raise validation_exc.ValueValidationException(six.text_type(e))

        liveaction_db, execution_db = action_service.request(liveaction_db)

        return execution_db

        Schedule an action execution.

        :type action_exec_spec: :class:`ActionExecutionSpecDB`

        :param params: Partially rendered parameters to execute the action with.
        :type params: ``dict``

        :rtype: :class:`LiveActionDB` on successful scheduling, None otherwise.
        
st2reactor/st2reactor/rules/enforcer.py