watcher-specs/specs/newton/implemented/configurable-weights-default-planner.rst

Make default Planner generic

https://blueprints.launchpad.net/watcher/+spec/configurable-weights-default-planner

Problem description

Watcher provides a very modular architecture that currently allows anyone to provide custom plugins:

• Strategy
• Planner
• Action
• Workflow Engine

In most of the above, their related implementation(s) are generic enough so that they can work with any 3rd party plugin out of the box. However, this is currently not the case for the defaultplanner which defines a hardcoded set of priorities for each action type.

Hence, this means that adding a new Action via an action plugin and reference it in a strategy would result in an error and the only solution is to create a planner plugin that would adapt to this new action.

This is not very user friendly for the Watcher users because this means that every time someone adds a new action, the source code of the planner will have to be amended.

Use Cases

As an administrator, I would like to be able to add a new Action without having to amend the source code of the defaultplanner.

Project Priority

• Medium

Proposed change

This specification suggests modifying the DefaultPlanner class watcher/decision_engine/planner/default.py in order to avoid having to implement a new planner whenever adding a new action plugin to the mix. A simple solution to this would be to leverage the plugins-parameters blueprint so that we can configure weights via the configuration file.

Currently in watcher, the weights are defined as below: :

priorities = {
        'nop': 0,
        'sleep': 1,
        'change_nova_service_state': 2,
        'migrate': 3
}

We have to replace this by the code below :

self.weights_dict = {'nop': 0,
                'sleep': 1,
                'change_nova_service_state': 2,
                'migrate':3}
def get_config_opts(self):
return [
cfg.DictOpt('weights', help="These weights are used to schedule
    the Actions.",
    default=self.weights_dict),
    ]

Alternatives

None

Data model impact

None

REST API impact

None

Security impact

None

Notifications impact

None

Other end user impact

The user will have to modify the configurable file and reboot the decision engine.

Performance Impact

None

Other deployer impact

We are adding a new field in the configuration file. So, we should revisit the puppet scripts.

Developer impact

None

Implementation

Assignee(s)

Primary assignee: Jinquan Ni <ni.jinquan@zte.com.cn>

Work Items

• Replace the storage of the weights in the default planner
• Update the documentation
• add unit tests

Dependencies

None

Testing

• Unit tests will be added to validate these modifications.

Documentation Impact

Update the defaultplanner documentations to now mention that the weights of the planner can be specified in the configuration file.

References

History

None