Design, Implementation and Evaluation of an Event

Service

by Kiran Anna

Temitope Alo

CDA 5937Spring 2002

Roadmap

• Introduction• Motivation• Event Service• Proposed Work

– Objectives– Design criteria

• Background• Literature

Introduction

• Increased Focus on complex distributed software systems that execute and interoperate over the Internet

• Why distributed software systems over internet?

Introduction contd.

• Distributed software systems– loosely coupled– heterogeneity– computing power

• Demand for suitable architecture styles and related run time infrastructures

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

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

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

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

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

Internet-Scale Event Service Contd.

Publish events

Event Service

Component1

Component2 Component4

Component3

Subscribe events

Notify events

Internet-Scale Event Service Contd.

Subscribe events

Event Service

Component1

Component2Safety Manager

B

ControllerA

Notify events

Publish events

Fire outbreak

Someone in danger

A – take actions on reception of fire alarmB – Call the rescue team

Proposed Work

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

Approach to designing the ES System

• Start with a basic event model

CREATOR

Publishers

Subscribers

Rendezvous point

EVENT SERVICE1

2

3

41 – Create Rendezvous Point

2 – Clients Subscribe

3 – Another Client Publishes

4 – Event Service notifies Subscriber

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.

Design Criteria• Subscription mechanism

Mechanism that supports the selection of subscribers to be notified of events

• Structure of notificationConsideration on event patterns using expressions over name and parameterse.g Alarm notification: Alarm(Room4, Fire Outbreak)

Subscription: Alarm*( __ , __ )

• Scalability propertiesScaling will be considered along the following dimensions:- number of subscribers and publishers- number of event subscription points- rates of event delivery

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 MethodShould communication between Publisher Server and Server Subscriber be a programmed interaction or human initiated interaction?

Design Criteria• Filtering

Should subscribers be delivered all available events or only events in which they are interested?

• Security IssuesPossibility 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?

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

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

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

Background contd.

• Tibco (TIB/Rendezvous)

– based on the subject as in smartsockets

– drawbacks• non-flexible

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

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

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

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

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