Design, Implementation and Evaluation of an Event Service

1. Design, Implementation and Evaluation of an Event Service by Kiran Anna Temitope Alo CDA 5937 Spring 2002

2. Roadmap • Introduction • Motivation • Event Service • Proposed Work • Objectives • Design criteria • Background • Literature

3. Introduction • Increased Focus on complex distributed software systems that execute and interoperate over the Internet • Why distributed software systems over internet?

4. Introduction contd. • Distributed software systems • loosely coupled • heterogeneity • computing power • Demand for suitable architecture styles and related run time infrastructures

5. Introduction Contd… • Emerging middleware architecture • based on the notion of event • distributed software components interact by generating and consuming events • This paradigm supports a flexible and effective interaction among highly re-configurable distributed software components

6. Introduction Contd.. • Event based architecture • The common infrastructure underlying event based systems is event service. • An event service is a facility that provides for observation and notification of events among the components. • Well developed for local area networks • Broadcast mechanisms • Vector clocks

7. Motivation • Bond • Middleware infrastructure • Being developed to support applications to execute over the internet • Absence of mechanism to connect the distributed software components over the internet • Lack of technologies to support event service at the scale of internet

8. Internet-Scale Event Service • Components communicate by generating and receiving event notifications • A component generates an event to inform the external world about a change in its internal state or in the state of other components with which it interacts

9. Internet-Scale Event Service Contd.. • When an event notification is generated, it is propagated to any component that has declared interest in receiving it. • The event generation and its propagation are performed asynchronously. • Connector (Event Service) • In charge of managing the propagation of event notifications

10. Notify events Component1 Component3 Event Service Component4 Component2 Subscribe events Internet-Scale Event Service Contd. Publish events

11. Event Service Internet-Scale Event Service Contd. Notify events Fire outbreak Component1 Controller A Safety Manager B Component2 Someone in danger Publish events Subscribe events A – take actions on reception of fire alarm B – Call the rescue team

12. Proposed Work

13. Objectives • Explore the existing design space of event based architecture • Design an internet-scale event service which supports • Scalability • Well defined class of events, taxonomy and the notification structure • efficient delivery mechanism to the subscribers • Failure recovery

14. Approach to designing the ES System • Start with a basic event model Publishers EVENT SERVICE 3 1 CREATOR Rendezvouspoint 2 4 Subscribers 1 – Create Rendezvous Point 2 – Clients Subscribe 3 – Another Client Publishes 4 – Event Service notifies Subscriber

15. Approach to designing the ES System • Event Service will include an abstraction(Rendezvous point) to which event publications are sent and to which subscribers make a request. • A protocol will be designed for clients to subscribe to the Rendezvous point. • A protocol will be designed for another client to publish an event to the Rendezvous point. • The Event Service System will have another protocol that sends the event received from the publisher to the subscriber.

16. Design Criteria • Subscription mechanism Mechanism that supports the selection of subscribers to be notified of events • Structure of notification Consideration on event patterns using expressions over name and parameters e.g Alarm notification: Alarm(Room4, Fire Outbreak) Subscription: Alarm*( __ , __ ) • Scalability properties Scaling will be considered along the following dimensions: - number of subscribers and publishers - number of event subscription points - rates of event delivery

17. Design Criteria • Failure Handling - In the presence of broken and disconnected components (publishers / subscribers) or broken communication link, Event Service System should still operate correctly. - Queuing events for disconnected clients until they reconnect • Interaction Method Should communication between Publisher Server and Server  Subscriber be a programmed interaction or human initiated interaction?

18. Design Criteria • Filtering Should subscribers be delivered all available events or only events in which they are interested? • Security Issues Possibility of restricting publishers / subscribers via access control to authenticated authorized parties • Event History - Should System allow subscribers to request a history of published events (in case of disconnection)? - How much of it will be allowed without overloading the Event Service System?

19. Background • Interest in event-based style has resulted in the development of a number of event-based middle ware infrastructures • These variations have an impact on the structure, the behavior, and the performance of the applications built on top of them

20. Background Contd. • CORBA • defines a simplified event service mechanism called channel • All the recipients that are connected to a channel receive all the notifications that are published by objects on that channel • drawbacks • non-scalability • non-flexible

21. Background contd. • Smartsockets • accepts subscriptions based on subjects • notifications are characterized by subject and data parts • A component receives all the event notifications that belong to the subjects to which it has subscribed • drawbacks • non-flexible

22. Background contd. • Tibco (TIB/Rendezvous) • based on the subject as in smartsockets • drawbacks • non-flexible

23. Background contd. • Elvin • content based subscription • notifications are sets of named and typed data elements • Subscription is a declarative boolean expression over the components of event notifications • a component can declare its interest in a number of notifications characterized by some common property

24. Background contd. • JEDI • provides a similar mechanism for event subscription • notification is defined by a name and by a number of parameters • example: Alarm(PC1,HALTED) is a notification whose name is Alarm and has two parameters whose values are PC1 and HALTED • event receivers subscribe for event patterns which are expressions over the name and parameters of notification

25. Background contd. • SIENA • currently under development • content-based with patterns • aims at maximizing expressiveness in the selection mechanism without sacrificing scalability of the delivery mechanism

26. Literature • Antonio Carzaniga, Elisabetta Di Nitto, David S. Rosenblum, and Alexander L.Wolf. Issues in Supporting Event-based Architectural Styles. ACM 1998, pg 17 – 20 • H.Yu, D.Estrin, and R.Govindan. A hierarchical proxy architecture for Internet-scale event services. Technical Report 99-704, Dept of Comp. Sci., univ. of Southern Calif., Mar. 1999 • G.Cugola, E. Di Nitto, and A.Fuggetta, “Exploiting an Event-based Infrastructure to Develop Complex Distributed Systems”, In Proceedings of the 20th International Conference on Software Engineering, Kyoto, Japan, April 1998 • Antonio Carzaniga and Alexander L.Wolf. Design and Evaluation of a Wide-Area Event Notification Service. ACM Transactions on Computer Systems, Vol. 19, No. 3, August 2001, pg 332-383 • D.S. Rosenblum and A.L. Wolf. A Design Framework for Internet-Scale Event Observation and Notification. In Proceedings of the sixth European Software Engineering Conference, Zurich, Sept.1997

27. Literature Contd… • Daniel J. Barrett, Lori A. Clarke, Peri L. Tarr, and Alexander E.Wise. A Framework for Event-Based Software Integration. ACM Transaction on Software Engineering and Methodology, Vol.5, No. 4, October 1996, pg 378-421 • V.Tsaoussidis, H. Badr, L. Na, J. Song. A CORBA-based Application Service Middleware Architecture and Implementation. IEEE 1999, pg 130-136 • Antonio Carzaniga, D.S Rosenblum and A.L Wolf. Design of a Scalable Event Notification Service: Interface and Architecture. Univ. of Colorado, Dept. of Comp. Sci., Technical Report, August 1998. • Masoud Mansouri-Samani and Morris Sloman. A configurable Event Service for Distributed Systems. 1996 IEEE, pg 210 – 217 • Antonio Carzaniga, D.S Rosenblum and A.L Wolf. Interfaces and Algorithms for a Wide-Area Event Notification Service. Univ. of Colorado, Dept. of Comp. Sci., Technical Report, Oct. 1999