Queue Consumer

Queue Consumer

https://blueprints.launchpad.net/octavia/+spec/queue-consumer

This blueprint describes how Oslo messages are consumed, processed and delegated from the API-controller queue to the controller worker component of Octavia. The component that is responsible for these activities is called the Queue Consumer.

Problem description

Oslo messages need to be consumed by the controller and delegated to the proper controller worker. Something needs to interface with the API-controller queue and spawn the controller workers. That “something” is what we are calling the Queue Consumer.

Proposed change

The major component of the Queue Consumer will be a class that acts as a consumer to Oslo messages. It will be responsible for configuring and starting a server that is then able to receive messages. There will be a one-to-one mapping between API methods and consumer methods (see code snippet below). Corresponding controller workers will be spawned depending on which consumer methods are called.

The threading will be handled by Oslo messaging using the ‘eventlet’ executor. Using the ‘eventlet’ executor will allow for message throttling and removes the need for the controller workers to manage threads. The benefit of using the ‘eventlet’ executor is that the Queue Consumer will not have to spawn threads at all, since every message received will be in its own thread already. This means that the Queue Consumer doesn’t spawn a controller worker, rather it just starts the execution of the deploy code.

An ‘oslo_messaging’ configuration section will need to be added to octavia.conf for Oslo messaging options. For the Queue Consumer, the ‘rpc_thread_pool_size’ config option will need to be added. This option will determine how many consumer threads will be able to read from the queue at any given time (per consumer instance) and serve as a throttling mechanism for message consumption. For example, if ‘rpc_thread_pool_size’ is set to 1 thread then only one controller worker will be able to conduct work. When that controller worker completes its task then a new message can be consumed and a new controller worker flow started.

Below are the planned interface methods for the queue consumer. The Queue Consumer will be listening on the OCTAVIA_PROV (short for octavia provisioning) topic. The context parameter will be supplied along with an identifier such as a load balancer id, listener id, etc. relevant to the particular interface method. The context parameter is a dictionary and is reserved for metadata. For example, the Neutron LBaaS agent leverages this parameter to send additional request information. Additionally, update methods include a *_updates parameter than includes the changes that need to be made. Thus, the controller workers responsible for the update actions will need to query the database to retrieve the old state and combine it with the updates to provision appropriately. If a rollback or exception occur, then the controller worker will only need to update the provisioning status to ERROR and will not need to worry about making database changes to attributes of the object being updated.

def create_load_balancer(self, context, load_balancer_id):
    pass

def update_load_balancer(self, context, load_balancer_updates,
                         load_balancer_id):
    pass

def delete_load_balancer(self, context, load_balancer_id):
    pass

def create_listener(self, context, listener_id):
    pass

def update_listener(self, context, listener_updates, listener_id):
    pass

def delete_listener(self, context, listener_id):
    pass

def create_pool(self, context, pool_id):
    pass

def update_pool(self, context, pool_updates, pool_id):
    pass

def delete_pool(self, context, pool_id):
    pass

def create_health_monitor(self, context, health_monitor_id):
    pass

def update_health_monitor(self, context, health_monitor_updates,
                          health_monitor_id):
    pass

def delete_health_monitor(self, context, health_monitor_id):
    pass

def create_member(self, context, member_id):
    pass

def update_member(self, context, member_updates, member_id):
    pass

def delete_member(self, context, member_id):
    pass

Alternatives

There are a variety of ways to consume from Oslo messaging. For example, instead of having a single consumer on the controller we could have multiple consumers (i.e. one for CREATE messages, one for UPDATE messages, etc.). However, since we merely need something to pass messages off to controller workers other options are overkill.

Data model impact

While there is no direct data model impact it is worth noting that the API will not be persisting updates to the database. Rather, delta updates will pass from the user all the way to the controller worker. Thus, when the controller worker successfully completes the prescribed action, only then will it persist the updates to the database. No API changes are necessary for create and update actions.

REST API impact

None

Security impact

None

Notifications impact

None

Other end user impact

None

Performance Impact

The only performance related item is queue throttling. This is done by design so that operators can safely throttle incoming messages dependent on their specific needs.

Other deployer impact

Configuration options will need to be added to ocativa.conf. Please see above for more details.

Developer impact

None

Implementation

Assignee(s)

jorge-miramontes

Work Items

  • Implement consumer class
  • Add executable queue-consumer.py to bin directory

Testing

Unit tests

Documentation Impact

None

References

None

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