oslo.messaging: Notification listener pools

https://blueprints.launchpad.net/oslo.messaging/+spec/notification-listener-pools

The idea is that you can have multiple groups/pools of listeners consuming notifications and that each group/pool only receives one copy of each notification.

Problem description

Currently if two applications use the oslo.messaging notification listener and want to subscribe to the same topic, they steal messages from each other.

The current workaround is to configure the notifier part to publish the message twice on different topic. This confuses a lot of people and this is undocumented.

Proposed change

So part of the purpose of this BP is a bit hardcoded into oslo.messaging and have bad side effect. The proposal will fix that.

We need to add a pool parameter for the messaging.get_notification_listener() API in order to support this.

In all AMQP drivers, this is implemented by using the pool name as the queue name for consume from the topic. To keep backward compatibility, by default, the topic name will continue to be used as the pool/queue name.

Alternatives

Documents the workaround.

Impact on Existing APIs

oslo.messaging.get_notification_listener will get a new parameter ‘pool’ to configure the pool name.

Security impact

None.

Performance Impact

None.

Configuration Impact

None.

Developer Impact

None.

Testing Impact

None.

Implementation

Assignee(s)

Primary assignee:
sileht
Other contributors:
None

Milestones

K-1

Work Items

Works already done: https://review.openstack.org/125112

Incubation

None.

Adoption

None.

Library

None.

Anticipated API Stabilization

None.

Documentation Impact

The new pool parameter will be documented.

Dependencies

None.

References

Code in review: https://review.openstack.org/#/c/125112/

Note

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