Merge "Add improvements to the planner and workflow mechanisms"
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specs/ocata/approved/planner-storage-action-plan.rst
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specs/ocata/approved/planner-storage-action-plan.rst
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..
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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=====================================
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Improve the storage of the ActionPlan
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=====================================
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https://blueprints.launchpad.net/watcher/+spec/planner-storage-action-plan
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Problem description
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===================
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`Action plan`_ is built by the default `planner`_ of the `decision-engine`_
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service. Every `Action`_ is linked to the next one so we have linked list
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of Actions as result of default planner's work. `Applier`_ service executes
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the action plan. Launching actions in a sequence has negative influence
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on performance, especially if there are a lot of actions. Every action
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must be completed before next action will be run, so it will take
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a lot of time to launch migration actions in sequence.
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Use Cases
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----------
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As an administrator, I would like to be able to run Action plan that will
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launch actions for every node (compute, network, storage) in parallel.
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Proposed change
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===============
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We can launch several concurrent actions with the same action weight in
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parallel.
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This specification defines two different planner with the same input/output
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dataflow: weight planner and workload stabilization planner. Each planner
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should use new ``parents`` attribute that will store list of actions the
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action is linked to, but there are different ways to fill up this attribute.
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Weight planner is designed to get unified way to parallelize execution
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of actions. It knows nothing about structure of specified actions and how they
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are related to each other. The main goal is to build sets of actions ordered by
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their weights. Administrator can specify each action type's weight and its
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parallelization ability.
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Let's show example of acyclic directed graph for this planner:
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::
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---sleep2 ---migration1 ---resize1
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/ \ / \ / \
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I----sleep1-------migration2------resize2----resize3----E
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\ /
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---migration3
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This graph is built with the following settings:
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+-----------+--------+-----------------+
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| | Weight | Parallelization |
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+===========+========+=================+
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| Sleep | 70 | 2 |
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+-----------+--------+-----------------+
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| Migration | 60 | 3 |
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+-----------+--------+-----------------+
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| Resize | 50 | 2 |
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+-----------+--------+-----------------+
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Since there are three resize actions and only two are allowed to be executed
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at the same time, the third resize action will be executed only when
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the previous actions are done.
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Weight planner is easy to configure and has to be considered
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as new default planner.
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Workload Stabilization planner respects features of action types by allowing
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to affect on building of ``parents``. Some action types like resizing
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the instance should be run only before/after migration of the same instance,
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not in parallel. There are to be specified some constraints:
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* Unlinked actions are to be performed in parallel.
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* Only one action can be performed per instance at one time
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* If there are more than one action per instance, linked actions must be
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executed in sequence with respect to action weights.
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So we can add new attribute ``parents`` that will store list of actions
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the current action is linked to. It can be shown using
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the acyclic directed graph:
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::
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----------------a1(t=dis)-----------
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/ \
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| \
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| ----------------a2(t=mig)-------------\
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|/ \
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I-----a3(t=mig) -- a31(t=res)---------------E
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|\ /
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| ----------a4(t=resize)----------------/
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| /
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\ /
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a5(resource=123, -- a51(resource=123,
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t=mig) t=resize)
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Here we can see the following links:
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* a1 action disables the compute node and is not linked with another action.
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It can be run in parallel with other action (there is no constraint).
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* a2 action migrates the instance and is not linked with another action.
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It can be run in parallel with other action (there is no constraint).
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* a3 action migrates the instance and is parent to a31 action.
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It can be run in parallel with other action.
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* a31 action resizes an instance after this last one had been migrated
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by action a3.
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* a4 action resizes the instance and is not linked with another action.
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It can be run in parallel with other action (there is no constraint).
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* a5 action migrates the instance and is parent to a51 action.
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It can be run in parallel with other action.
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* a51 action resizes the same instance after this last one had been migrated
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by action a5.
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As we can see, all actions that are independent to each other can be performed
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in parallel. Meanwhile, if some actions are linked to the same resource then
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they are to be performed with respecting to action weights. Currently, we can
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define the following weights:
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* End of graph - 0
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* Disable Compute Node - 1
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* Resize instance - 2
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* Migrate instance - 3
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* Initial point - 4
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There is estimated pseudocode to show part of workload stabilization
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planner's workflow::
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action = [uuid, type, resource_id, metadata]
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init = Flow()
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action_weights = {
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'turn_host_to_acpi_s3_state': 0,
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'resize': 1,
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'migrate': 2,
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'sleep': 3,
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'change_nova_service_state': 4,
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'nop': 5,
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}
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actions = sorted_by_weights(descended)
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for action in actions:
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a_type = action['action_type']
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if a_type != 'turn_host_to_acpi_s3_state':
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db_action = self._create_action(context, action)
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plugin_action = self.load_child_class(
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db_action.action_type)
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parents = plugin_action.validate_parents(
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resource_action_map, action)
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if parents:
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db_action.parents = parents
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db_action.save()
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else:
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# if we have an action that will make host unreachable, we need to
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complete all actions (resize and migration type) related to the
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host.
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parent_actions = get_actions(metadata=action[metadata][host])
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resize_actions = [x for x in parent_actions if x[type] == resize]
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migration_actions = [x for x in parent_actions if x[type] == mig]
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resize_migration_parents = [x[parents] for x in resize_actions]
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# Since resize actions have less weight than migration, they may
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have migration actions as parents and must be connected to the
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turn_host_to_acpi_s3_state action firstly.
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action_parents = []
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action_parents.extend([x[uuid] for x in resize_actions])
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# Add migrations that aren't linked to resize type actions
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action_parents.extend([x[uuid] for x in migration_actions
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if [x[uuid]] not in resize_migration_parents)
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db_action = create_action(action, parents=action_parents)
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This spec is limited to simple chained list of actions as action plan. The
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second part of modifying action plan's executing will contain graph for
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parallel executing of action plans.
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Alternatives
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------------
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None
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Data model impact
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-----------------
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* ``next`` column should be removed from the Action table.
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* ``parents`` column should be added to the Action table. Type: JSON.
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* ``first_action_id`` column should be removed from Action Plan table.
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* ActionPlan object major version should probably be updated to 2.0
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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None
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Performance Impact
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------------------
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None
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Other deployer impact
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---------------------
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None
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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Alexander Chadin <a.chadin@servionica.ru>
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Other contributors:
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Vincent Francoise <Vincent.FRANCOISE@b-com.com
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Work Items
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----------
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* Update data model in accordance with proposed changes
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(in fact API and objects).
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* Remove default planner.
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* Add watcher/decision_engine/planner/weight.py and
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watcher/decision_engine/planner/workload_stabilization.py
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* Make weight planner as default.
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* Update the documentation.
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* Add appropriate unit tests.
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Dependencies
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============
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https://blueprints.launchpad.net/watcher/+spec/plugins-parameters
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Testing
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=======
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* Unit tests will be added to validate these modifications.
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Documentation Impact
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====================
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Update the `defaultplanner`_ documentation in accordance with new changes.
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References
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==========
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.. _Applier: http://docs.openstack.org/developer/watcher/glossary.html#watcher-applier
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.. _Action plan: http://docs.openstack.org/developer/watcher/glossary.html#action-plan
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.. _Action: http://docs.openstack.org/developer/watcher/glossary.html#action
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.. _defaultplanner: https://github.com/openstack/watcher/blob/master/watcher/decision_engine/planner/default.py#L31
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.. _decision-engine: http://docs.openstack.org/developer/watcher/glossary.html#watcher-decision-engine
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.. _planner: http://docs.openstack.org/developer/watcher/glossary.html#watcher-planner
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History
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=======
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None
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