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
Internet-Scale Event Service Contd.
Publish events
11
Internet-Scale Event Service Contd.
Notify events
Fire outbreak
Component1
Controller A

• Event Service

Safety Manager B
Component2
Someone in danger
Subscribe events
Publish 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
Rendezvous point
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(Rendezvo
  us 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