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From Isuru Haththotuwa <>
Subject Refactoring Event Receivers in Messaging Component
Date Thu, 03 Dec 2015 23:49:22 GMT
Hi Devs,

Started doing $subject. The Event Receiver model was designed when Stratos
cannot be run on a single JVM, and it was not properly re-factored once the
Stratos single JVM distribution came up. So, all the main components
(Stratos Manager, Cloud Controller, Autoscaler) has their own Message
Queues, Event Listeners, Processors and Processor Chains. However, the
Topology model is a common to all the components, therefore the we actually
have three sets of classes as mentioned above, updating the Topology. This
is unnecessary, the code is complex and hard to maintain.

This can be changed so that each JVM will have only a single set of Message
Queues, Event Listeners, Processors and Processor Chains of each event
type. All the other component who are interested in a particular event can
access the event receiver object and call addEventListener method to
register a listener to get notified on the relevant events.

The following are the main changes:

   1. Make all *EventReceiver classes singleton; Stratos will have one
   Event Receiver for main event categories (Topology, Tenant, Instance
   Status, Instance Notifier, Initializer, Health Stat, Domain Mapping,
   Cluster Status, Application and Signup) per JVM.
   2. Remove the multiple EventReceivers in the components (ex:.
   StratosManagerTopologyEventReceiver, AutoscalerHealthStatEventReceiver,
   etc.). Instead of creating multiple queues, delegators, processors and
   processor chains, they will now act like listeners for each processor.
   3. Rename the component specific event receiver classes to reflect their
   actual functionality.


Thanks and Regards,

Isuru H.
+94 716 358 048* <>*

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