Notification Dispatcher Filter

https://blueprints.launchpad.net/oslo?searchtext=notification-dispatcher-filter

Oslo.messaging lacks the ability to filter out notifications it sends to endpoints. This spec proposes to enable filtering process before messages are dispatched to endpoints.

Problem description

Currently, oslo.messaging blindly dispatches notifications to all registered endpoints. It is after the endpoints receive the messages are we able to filter and decide whether the endpoint should process the notifications. This decision can be made earlier before it dispatches messages to the endpoints to avoid the overhead of sending messages to endpoints which will ignore them.

For example, in Ceilometer, multiple endpoints are connected to the notification listener. Each endpoint may only process a subset of the notifications that are picked up. It is at the endpoint level where we currently filter whether to continue processing the notification but this filtering can easily be done before it’s even dispatched to the endpoint.

Proposed change

The proposed solution is to add a NotificationFilter to the dispatcher. When oslo.messaging dispatches messages to the endpoints, it will first pass through the filter and check if the messages fits the criteria defined in filter. Messages can be filtered using regex against all first level attributes of a message: context, publisher_id, event_type, metadata, and payload. As context, metadata, and payload are dictionary values, multiple contraints can be defined for them.

An example filter is as follows:

filter =  NotificationFilter(
    publisher_id='^compute.*',
    context={'tenant_id': '^5f643cfc-664b-4c69-8000-ce2ed7b08216$',
             'roles': 'private'},
    event_type='^compute\.instance\..*',
    metadata={'timestamp': 'Aug'}.
    payload={'state': '^active$'})

Alternatives

We continue to filter at the endpoint level.

Impact on Existing APIs

None.

Security impact

None.

Performance Impact

None, but it does offer potential to reduce load dispatched.

Configuration Impact

None.

Developer Impact

Developers nowi have ability to add a filter when they defined Endpoints.

class NotificationEndpoint(object):
    filter = NotificationFilter(publisher_id='^compute.*')

Testing Impact

Unit tests are sufficient as the functionality is limited to dispatcher. Indirectly, when implemented in Ceilometer, this will be tested via tempest.

Implementation

Assignee(s)

Primary assignee:
sileht
Other contributors:
gordc

Milestones

Target Milestone for completion: kilo-1

Work Items

  • Add filter to dispatcher with unit tests
  • change filters in Ceilometer to use new filters.

Incubation

None.

Adoption

Ceilometer but it seems like common functionality that other listeners would use.

Library

oslo.messaging.

Anticipated API Stabilization

None.

Documentation Impact

None.

Dependencies

None.

References

code review: http://review.openstack.org/#/c/77886/

Note

This work is licensed under a Creative Commons Attribution 3.0 Unported License. http://creativecommons.org/licenses/by/3.0/legalcode