Java Mobile Agents with Aglets Wolfgang Schreiner [email protected].

Java Mobile AgentsJava Mobile Agentswith Agletswith Aglets

Wolfgang [email protected]

Chapter 1 – Chapter 1 –

Introduction to Mobile AgentsIntroduction to Mobile Agents

What is a Software Agent?What is a Software Agent?

End-User Perspective– An agent is a program that assists people and acts

on their behalf– Agents function by allowing people delegate

work to them

System Perspective– An agent is a software object that is situated

within an execution environment– possesses mandatory and orthogonal properties

What is a Mobile Agent?What is a Mobile Agent?

Stationary Agent– executes only on the system where it begins execution– interacts with an agent using communication mechanisms

Mobile Agent– not bound to the system where it begins

execution– has the ability to transport itself from one system

in a network to another

Reasons for Mobile AgentsReasons for Mobile Agents

Reduce network load Reduce network latency Encapsulate protocols Execute asynchronously and

autonomously Adapt dynamically Are naturally heterogeneous Are robust and fault-tolerant

Network ComputingNetwork Computing

Client-Server Paradigm– A server locally hosts services that provide

access to resources and code that implements these services.

Code-on-Demand Paradigm– no preinstalled code on the client side

Mobile Agent Paradigm– hosts are allowed a high degree of flexibility

Mobile Agent ApplicationsMobile Agent Applications

Electronic Commerce Personal assistance Distributed information retrieval Telecommunication network services Workflow applications and groupware Monitoring and notification Parallel processing

Mobile Agent SystemsMobile Agent Systems

Java– Aglets

– Odyssey– Concordia– Voyager

Others– Agent Tcl– Ara– TACOMA

Mobile Agent StandardizationMobile Agent StandardizationMASIFMASIF

Agent managementAgent transferAgent and agent system namesAgent system type and location

syntax

Chapter 2 – Chapter 2 –

Elements of aElements of aMobile Agent SystemMobile Agent System

Agent ...Agent ...

... and Place... and Place

Agent Behaviour (1)Agent Behaviour (1)

Creation– Instantiation and identifier assignment

– Initialization

– Autonomous execution

Disposal– Preparing for disposal

– Suspension of execution

Agent Behaviour (2)Agent Behaviour (2)

Dispatching– Suspend, serialize, encode, transfer

Receiving– Receive, decode, de-serialize, resume execution

Agent Class Transfer– Class at destination– Class at origin– Code-on-demand

CommunicationCommunication

MASIFMASIF

MAFAgentSystem Interface– agent management tasks

MAFFinder Interface– agent naming service

Chapter 3 –Chapter 3 –

Mobile Agents with JavaMobile Agents with Java

Java Agents - BenefitsJava Agents - Benefits

Platform IndependenceSecure ExecutionDynamic Class LoadingMultithread ProgrammingObject SerializationReflection

Java Agents - DrawbacksJava Agents - Drawbacks

Inadequate Support for Resource Control

No Protection of ReferencesNo Object Ownership of ReferencesNo Support for Preservation and

Resumption of the Execution State

The Aglet ModelThe Aglet Model

Basic Elements– aglet, proxy, context, identifier

– creation, cloning, dispatching, retraction, disposal, activation/deactivation

Aglet Event Model– clone, mobility and persistence listener

Aglet Communication Model– Message, FutureReply, ReplySet

Aglet PackageAglet Package

class Agletinterface AgletProxyinterface AgletContextclass Messageclass FutureReplyclass AgletID


Anatomy of an AgletAnatomy of an Aglet

Aglet DisposalAglet Disposal

public final void Aglet.dispose(); public void Aglet.onDisposing();

Example:

public class DisposalExample

extends Aglet {

public void onDisposing() { ... }

public void run() {

dispose();

}

}

Delegation-Based Event Delegation-Based Event ModelModel

CloneEvent, MobilityEvent, PersistencyEvent

CloneListener, MobilityListener, PersistencyListener

CloneAdapter, MobilityAdapter, PersistencyAdapter

CloningCloning

public final Object Aglet.onClone();

public final void Aglet.addCloneListener(CloneListener);

public final void Aglet.removeCloneListener(CloneListener);

public void CloneAdapter.onCloning(CloneEvent);

public void CloneAdapter.onClone(CloneEvent); public void CloneAdapter.onCloned(CloneEvent);

Aglet MobilityAglet Mobility

public final void Aglet.dispatch(URL); public final void

Aglet.addMobilityListener(MobilityListener); public final void

Aglet.removeMobilityListener(MobilityListener); public void

MobilityAdapter.onDispatching(MobilityEvent); public void

MobilityAdapter.onArrival(MobilityEvent); public void

MobilityAdapter.onReverting(MobilityEvent);

PersistencePersistence

public final void deactivate(long); public final void Aglet.addPersistencyListener

(PersistencyListener); public final void

Aglet.removePersistencyListener (PersistencyListener);

public void PersistencyAdapter.onDeactivating (PersistencyEvent);

public void PersistencyAdapter.onActivation (PersistencyEvent);

EventsEvents

CloneEventMobilityEvent

– public URL MobilityEvent.getLocation();

PersistencyEvent– public long

PersistencyAdapter.getDuration();


Aglet ContextAglet Context

Aglet CreationAglet Creation

Code and Code Base

Code Base and Class Mobility

Initialization Argument

Proxy RetrievalProxy Retrieval

Proxy Iterator– public abstract Enumeration

AgletContext.getAgletProxies();

Getting a Local Proxy– public abstract AgletProxy

AgletContext.getAgletProxy(AgletID);

Getting a Remote Proxy– URL as additional parameter

Aglet RetractionAglet Retraction

public abstract AgletProxy AgletContext.retractAglet(URL,AgletID);

Example:

AgletID aid=proxy.getAgletID();

Proxy.dispatch(dest);

getAgletContext().retractAglet(dest,aid);

Context PropertiesContext Properties

public abstract Object AgletContext.getProperty(String);

public abstract Object AgletContext.getProperty(String,Object);

public abstract void AgletContext.setProperty(String,Object);


Aglet MessagingAglet Messaging

Simple MessagingSimple Messaging

public Object AgletProxy.sendMessage(Message); public boolean Aglet.handleMessage(Message);

The The MessageMessage Class Class

Message Creation– public Message(String [,…] );

Receiving Messages– getArg, setArg, getKind, sameKind

Replying to Messages– public void Message.sendReply();– public void

Message.sendException(Exception);

Getting the ReplyGetting the Reply

Message ManagementMessage Management

Serialized Message HandlingMessage PrioritiesParallel Message HandlingSynchronized Message Handling

MulticastingMulticasting

public final void Aglet.subscribeMessage(String);

public final void Aglet.unsubscribeMessage(String);

public final void Aglet.unsubscribeAllMessages();

public ReplySet AgletContext.multicastMessage(Message);

Receiving Multiple RepliesReceiving Multiple Replies

public boolean ReplySet.hasMoreReplies();

public FutureReply ReplySet.getNextFutureReply();

public boolean ReplySet.addFutureReply(FutureReply);


Aglet CollaborationAglet Collaboration

Aglet ProxyAglet Proxy

CloningDisposalDispatchingDeactivation and ActivationAglet Information

Controlling an AgletControlling an Aglet

Finding an AgletFinding an Aglet

SearchLoggingRegistrationAgletFinder

– Lookup: NAME

– Register: NAME & PROXY

– Unregister: NAME

Aglets in Parallel ExecutionAglets in Parallel Execution


Agent Design PatternsAgent Design Patterns

Design Pattern ClassificationDesign Pattern Classification

Traveling Patterns– Itinerary, Forward, Ticket

Task Patterns– Master-Slave

Interaction Patterns– Meeting, Locker, Messenger, Finder, Organized Group


Inside AgletsInside Aglets

Architectural OverviewArchitectural Overview

Core Framework– Initialization and (de-)serialization– Class loading and transfer– Aglet references and garbage collection

Management Components– PersistencyManager– CacheManager– SecurityManager

Communication Layer

Aglet Object StructureAglet Object Structure

Initialization and SerializationInitialization and Serialization

Initialization of Aglets– Locate aglet class, load class data, define class

– Instantiate new object

– Create reference AgletRef, establish connection

– Start execution

Serialization and Object Mobility

Class Loading and TransferClass Loading and Transfer

Class LoadingClass Transfer

– Archived classes

– Code base classes– System classes– Others

Class Resumption and EvolutionOther Considerations of Class

Mobility

Communication LayerCommunication Layer

Communication API– MASIF

Agent Transfer Protocol– Dispatch

– Retract

– Fetch

– Message


Aglet SecurityAglet Security

What Can Go Wrong?What Can Go Wrong?

Agent Protection– Remote host threatens agent– Agent threatens another agent– Unauthorized third parties threaten agent

Host Protection– Incoming agent threatens host

– Unauthorized third parties threaten host

Network protection– Incoming agent threatens the network

Taxonomy of AttacksTaxonomy of Attacks

Passive Attacks– Eavesdropping

– Traffic Analysis

Active Attacks– Illegal Access – Replay

– Masquerade – Resource Exhaustion

– Trojan Horse – Repudiation

– Alteration

Security ServicesSecurity Services

Authentication– user, host, code, agent

IntegrityConfidentialityAuthorizationNonrepudiationAuditing

Security ModelSecurity Model

Principals– Aglet, Context and Server, Network Domain

Permissions– File, Network, Window, Context, Aglet

ProtectionsPolicy and Authority

– Aglet owner, Context owner, Network owner

Java Mobile Agents with Aglets Wolfgang Schreiner [email protected].

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Transcript of Java Mobile Agents with Aglets Wolfgang Schreiner [email protected].