An Application Framework For Event-driven, Re-configurable

Distributed Applications

M.RanganathanMultimedia and Digital Video Group

National Institute of Standards and Technology

Goals of the AGNI Project

• Design and build a secure , extensible, re-configurable, fault-tolerant middle-ware for peer-to-peer distributed applications.

• Develop peer-to-peer applications based on developed infra-structure.

• Evaluate architectures for Mobile Agent platforms via simulation.

Application Scenarios

• Distributed Event-driven applications:– Distributed testing, logging and monitoring.– Distributed control.– Conferencing, conference control.– Network Management.

Overview

• Built around the Mobile Streams abstraction.– A Mobile Stream is a named communication end-point.– Provides a FIFO ordering guarantee.– Name-location mapping can dynamically changed.

Basic idea: Start with the communication structure of the application.Attach handlers to communication end-points to define complete app.

Streams

STREAM (global name, ordering guarantee)

Handler Handler Handler

Messages

Overview

• Application is structured as a set of handlers that “react” to messages.

• System can be re-configured dynamically - Streams can be moved around in reaction to external changes.

Resource Control

• System is re-configurable and dynamically extensible– System can be extended by dynamically adding

Streams and handlers. – Reconfigured by moving around streams.

• Resource Control Mechanism – controls on mobility, message delivery,

reconfiguration, new stream creation and destruction.

Resource Control Mechanisms

• System-wide resource control.• Per-stream resource control.• Per-location resource control.

Application : Agent Monitor

• Track the location of agents in the distributed system.

• Reactive GUI application.• Allow user to easily deploy agents using a

GUI driven management tool.

Agent Monitor

Agent Debugger

• A tool to debug Agent Scripts.• Extension of tcl-debug debugger.• Goals:

– Location transparency.– Global stepping.– Global conditional breaks.

Agent Debugger Organization

Debugger GUI

Debugee Agent

Monitor Stream

MBOX

Per-locationController

Total ordering of messages

• Total order:– Messages can be sent concurrently.– Consumers consume messages in the same order.

• Application:– Collaborative sharing of unmodified Tk applications

using WYSIWIS model.– Dynamic reconfiguration to reduce latency.

Tk-Collaborative Toolkit

Event Dispatcher

Tk Application Tk Application

Tk Events Tk Events

Mobile

Tk Events Tk Events

Tk Events

Record and Replay of collaborative tools

• XCVW Multi-party conferencing tool.– Asynchronous interactions generated by each party.– Want to record the interactions while tool is being used

and replay tool live later keeping the same event sequencing.

– Live replay generates the same network load.• Joint work with MITRE (Supported by DARPA

under the IC&V project).• Uses the NIST Mobile Stream Infrastructure.

Organization

Causal Order via mobility• Can replace causal ordering of actions by

streams and FIFO messages (between streams).

A B AT2 T5T3

T6T1A

C

• Example: Sequence of actions to be performed on machines A B and C:

Applications: Testing and collaborative applications.

Application: Distributed Testing

• Simplifies the design and construction of distributed testers as follows:– Asynchronously and autonomous execution simplifies

logic to build testers.– Reduction of tester generated network load.– Reduction of control latency.– Encapsulation of protocols used in distributed testing.– Dynamic adaptation to failures.

Example

• Required sequence:– Start data producer at A.– Start data consumer at B.– Initiate the transfer of data from A to B– Report the timing.

• Agent :– Hop to A start producer– Hop to B start consumer– Hop back to A start transfer.– Gather result and report.

A Distributed web-based Test Harness

• A high level scripting environment to specify sequences of actions and execute them in a web-based environment.

T1

T3

T2T4

At location 2At location 1

At location 3

At location 1

Sequential { at 1 { do task T1 } concurrent {

at 2 {do task T2}at 3 {do task T3}

} at 1 {do task T4}}

Architecture

HTTPD

Browser Agnid Agnid Browser

Sequential { at 1 { do task T1 } concurrent {

at 2 {do task T2}at 3 {do task T3}

} at 1 {do task T4}}

Compiler

AGNI Streams Commands

System Organization

RELIABLECACHE/DIRECTORY MANAGER

CacheState

Control traffic

Unreliable Peer

Agent Daemon

CacheState

Unreliable Peer

Agent Daemon

Control traffic

Data

Hierarchical Directory Managers

Agent Daemon Organization

Stream (name)Stream (name)

LocationLocation

AgentAgent

Stream (name)Stream (name)

BriefcaseBriefcase

Tcl InterpTcl Interp

POSIX ThreadPOSIX Thread

AgentAgentBriefcaseBriefcase

Tcl InterpTcl Interp

POSIX ThreadPOSIX Thread

AgentAgentBriefcaseBriefcase

Tcl InterpTcl Interp

POSIX ThreadPOSIX Thread

AgentAgentBriefcaseBriefcase

Tcl InterpTcl Interp

POSIX ThreadPOSIX Thread

System Simulation

• We have built a complete simulation of system:– Most code re-used from actual implementation.– Underlying message interface is simulated.

• Allows experimentation with protocols and algorithms for re-configurable systems.

Future Plans

• Research Issues:– Security– Efficient inter-stream communication.– Resilience / Fault tolerance.

• Applications– Network management.– Distributed web-based testing.– Caching for collaborative applications.– Distributed resource-aware applications.