An An ExpressiveExpressive and and ScalableScalable XML Event Service XML Event Service for Service-Oriented Computingfor Service-Oriented Computing

Yi Huang

Extreme! Computing LabDepartment of Computer Science

Indiana University

Publish/Subscribe Event ServicesPublish/Subscribe Event Services

Subscribers express interests, later notified of relevant data from publishers Event (brokering) services manage subscriptions and deliver events Enable loosely-coupled application Integration

2

Scalability for Pub/Sub systemsScalability for Pub/Sub systems

Scalability: The capability of a system to maintain QoS under an increased load when resources are added.

– Scale up (add resource to a single node)

– Scale out (add more nodes) Load Scalability: The ability for a distributed system to easily expand its

resource pool to accommodate heavier loads.

– Number of publishers, Number of consumers,Number of subscriptions, Message rate (peak, average), Message size, etc

Geographic scalability– Accommodate clients (publisher/consumers) from Internet

Administrative scalability– Enable different organizations to share a publish/subscribe

service

3

Challenge: Expressiveness vs. ScalabilityChallenge: Expressiveness vs. Scalability

Has been treated as trade-offs in Publish/Subscribe systems Topic-based subscriptions need least processing power=>Best scalabilityContent-based subscriptions (name-value pair)

– More expressive

– consumers can get exact messages they need

– Reduce unnecessary transmission on WAN

– Need more processing power at each broker =>Less scalable

– Available Solutions: covering subscription (SIENA); organize attributes (Gryphon)

XPath-based Subscriptions – Filtering XML messages based on message structure and message content,

e.g. /a/b[@x=“1”]– Very expensive to parse XML messages and evaluate against XPath

subscriptions– Create more challenges to scalability

4

Examples of Content-based Filtering

Personalized news delivery– All the sports news.

– All the articles written by John Smith.

– All the articles referring to the one whose document id is 1234.

– All the events that will take place in Denver.

System monitoring– All the log message with “Error” as status.

– All the log messages from the simulation service.

Stock quotes– IBM stock value >100

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Applications of Event Brokering Services

Application integration Personalized news delivery Online auction Stock tickers Human resource management (Peoplesoft) Network and application monitoring …

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Infrastructure to Support Scientific Research

‘e-Science is about global collaboration in key areas of science, and the next generation of infrastructure that will enable it’

--John Taylor, Director General of Research Councils UK, Office of Science and Technology

Scientific research is becoming data centric– Unify theory, experiment, and simulation – Using data exploration and data mining– Data captured by instruments – Data generated by simulations– Processed by software– Scientist analyzes databases/files

Need International Grid Infrastructure to support e-Science.

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Services and SOA

Service: A “web server” that runs an application for you.– You send it requests (XML documents) and it processes the

information and send replies (notifications) when it is done.

Web service: Use standard web technology to create services, e.g. XML,SOAP, WSDL.

Service Oriented Architecture (SOA)– Promotes a pluggable framework to add new features and to

virtualize access to resources

Combining SOA and event service enables loosely-coupled system

Service1. Service Request

Bussiness Logic

2. Run Weather Simulation (WRF)

3. Publish notifications

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My Contributions in PhD

Participated in SOA design & implementation for eScience infrastructure in LEAD project

Created an Internet-scale Web-service-based Event service for SOA: The nerve system in the LEAD SOA– Made it reliable and scalable

– Integrated with various services

– Tools for management and debugging

Research problem addressed: Expressiveness vs. Scalability in XML Publish/Subscribe systems, especially the administrative scalability.

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OutlineOutline

Achieving Scalable and Expressive XML Event Services

Event Service in Service-oriented Scientific Workflow (LEAD project)

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Achieving Scalable and Expressive XML Event Services

Separation of concerns with a layered model– WS-Messenger local broker for XML and WS

– OpenPS broker network

Filtering Result Summary (FRS)– Reduce complicated event content matching to simple

string matching in the routing broker

Load Scalability in LAN

Achieved with – Message queue

– Load sharing among servers

– Load balancing

– Cache

Achieved in most commercial systems.– We use existing approaches in our systems.

– Not our research focus.

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Difficulties for Achieving Geographical Scalability

Long network latency, limited bandwidth

– RTT (from Indiana to Germany) is over 200 ms

Communication in WAN is inherently unreliable and virtually always point-to-point, whereas LAN communication is generally highly reliable and based on broadcasting

Centralized solutions lead to a waste of network resources and degrade system performance

Deployment, monitoring, updating and debugging Firewalls

– HTTP usually does not keep connections open

– Cost in initial three-way handshake on TCP

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Single Broker vs. Broker NetworkSingle Broker vs. Broker Network

InternetPublisher

Local consumer

Site A

Consumer 1

Consumer 3

Consumer 2

Consumer n

Single broker

...

Site B

Msg

Msg

Msg

Msg

Msg

Msg

InternetPublisher

Local consumer

Site A

Consumer 1

Consumer 3

Consumer 2

Consumer n

Broker A

...

Site B

Msg

Msg

Msg

Msg

Msg

Msg

Msg

Broker B

Internet

End client

Broker with router

Router only

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Duplicate transmissions of same messages

Take long time to get acknowledgements

Share the transmission bandwidth

Brokers take advantage of locality

Single Broker 2-Broker network

multi-Broker network

Filtering-based RoutingFiltering-based Routing

Subscription propagation: subscriptions are propagated to every broker leaving state along the path

Notification delivery: matching notification follow (backwards) the path set by subscriptions

Reducing subscription propagation– Avoiding subscription propagation when a filter

including the subscription has been already forwarded

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Difficulties for Achieving Administrative Scalability

Hindered by conflicting resource usage, management, and security policies in multiple, independent administrative domains

– E.g. Cannot trust a third-party service to inspect message content for content-based filtering

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Demands for Internet-scale Sharable ServicesDemands for Internet-scale Sharable Services

Emerging with the concept of using Internet as computing platform. Software-as-service Help developers build the next generation of composite

applications without maintaining infrastructure Require administrative scalability Amazon Simple Queue Service Amazon Simple Storage Service Microsoft BizTalk Service (instead of BizTalk server)

– newly announced 4/24/2007

– Added simple pub/sub support in 5/2/2007, allows multiple clients to subscribe to a service and receive notifications.

– Not production-level yet

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Related Work on Messaging MiddlewareRelated Work on Messaging Middleware

Topic-based Pub/Sub

Content -basedsimple Pub/Sub

Content-basedXML Pub/Sub

Geographic+Load

Load

Expressiveness

TIBCO, IBM MQ Series, Microsoft Biztalk Server,

SCRIBE,Bayeux, Echo

OpenJMS, activeMQ, Oracle Advanced

Queuing,Apache ServiceMix,

WS-Messenger

SIENA, Gryphon, HERMES, JEDI

Le Subscribe, Xlyeme, Elvin

ONYX, Xroute, NaradaBrokering,

Xfilter, Yfilter, Xaos, XSQ, Xtrie, IndexFilter,

XMLTLK,Apache ServiceMix,

WS-Messenger

Microsoft BizTalk Service,

OpenPSOpenPS

Amazon Simple Queuing Service OpenPS

Administrative+Geographic

+Load

Scalability

IBM MQ Series , Microsoft MQ ,Fiorano MQ,RabbitMQ

OpenJMS, activeMQ, Oracle Advanced

Queuing

Topic-based Queue

Limitation of Existing Content-based Pub/Sub ServicesLimitation of Existing Content-based Pub/Sub Services

Lack of administrative scalability (Not sharable) – Homogeneity: Require same broker to be deployed across the

Internet in every organization

– Need to trust brokers: Brokers need to inspect message content to make routing decision

– Not interoperable: Clients and brokers need same implementation, either C/C++ or Java library .

=>Not economical: Expensive to deploy and maintain global network for one project

Gap: – few projects can afford to deploy and maintain a global network,

– many projects need global messaging system. How to create a sharable Pub/Sub service?

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Our Solution: Separation of ConcernsOur Solution: Separation of Concerns

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Layered Publish/subscribe (LPS) Model 5-layered model built on top of TCP/IP model

LPS ModelLPS Model

InternetInternet

Event Application Layer

Event Transport Layer

Event Distribution Layer

Event Filtering Layer

Event Transformation Layer

Event Application Layer

Event Transport Layer

Event Distribution Layer

Event Filtering Layer

Event Transformation Layer

Event Transport Layer

Event Distribution Layer

Publisher Broker Consumer Broker

Intermediary Broker

Message Delivery

Message Delivery

publisher consumer

Broker Network

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Traditional approaches in distributed content-based filtering include all 5 layers in intermediary brokers.

Separation of ConcernsSeparation of Concerns

Separate brokers into local brokers and routing brokers Local brokers (WS-Messenger or other broker) are set up locally

– Users can trust to inspect message content

– Acts as local agents A global network of routing brokers (OpenPS network) can interact

with local brokers using Web service interfaces.– A brokering service for local brokers

– Handle global message dissemination

– Sharable by many local brokers

– Acts as postal offices Make the routing brokers as simple as possible

– Improve scalability and interoperability.

– Limitation of target deployment platform: PlanetLab global testbed• Shared virtual machines with CPU usage >95%.

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Hierarchical Broker NetworkHierarchical Broker Network

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Analogous to postal service networks Economies of scale

Filtering Result Summary (FRS)Filtering Result Summary (FRS)

Local brokers attach FRS to messages Observation 1: Topic-based message filtering in the

intermediary broker can be reduced to 1-to-1 string matching.

Observation 2: Content-based message filtering in the intermediary broker can be reduced to any-to-any string matching.

Simplify complicated message matching to string matching.

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Web service-based Event Service (WS-Messenger Local Event Service)

Focus on meeting the needs of local services ExpressivenessWeb servicesAddressing local load scalability

Y. Huang, A. Slominski, et al., "WS-Messenger: A Web Services based Messaging System for Service-Oriented Grid Computing," 6th IEEE International Symposium on

Cluster Computing and the Grid (CCGrid06).

New Requirements by SOA

Services are autonomous => may need format transformation

Integrate heterogeneous services and work with existing event buses– Java, C++, C#, Windows, Linux, Unix, OpenJMS, activeMQ,…

XML processing XPath-based filtering Internet-scale

– Services from different organizations in different locations

Shared global event service for SOA

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Evolution of Pub/Sub SpecificationEvolution of Pub/Sub Specification

CORBA (Common Object Request Broker Architecture) Event Service (3/1995)

CORBA Notification Service (6/1997) Java Message Service (JMS) (4/2002) OGSI-Notification (6/2003) WS-Notification (1/2004, OASIS standard 10/06) WS-Eventing (1/2004, submitted to W3C in 3/06)

Y. Huang and D. Gannon, "A Comparative Study of Web Services-based Event Notification Specifications," Proc. of Workshop on Web Services-based Grid Applications (WSGA), 2006

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WS-MessengerWS-Messenger Broker Broker

Implemented both WS-Eventing specification and WS-Notification specification

Mediation approach to reconcile conflicts between WS-Eventing and WS-Notification

A generic interface to wrap up existing local JMS messaging systems.

– Adapters created: OpenJMS, ActiveMQ, NaradaBrokering

Efficient XML processing– Over 4 times faster than Globus Toolkit implementation on XML message

processing

Support very expressive subscriptions

28Y. Huang, A. Slominski, et al., "WS-Messenger: A Web Services based Messaging System for Service-Oriented Grid Computing," (CCGrid06).

Architecture Architecture

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OpenPS Broker Network

Addressing Geographic scalability and Administrative scalabilityCreating a sharable global event service without losing expressiveness

Design Goals of OpenPSDesign Goals of OpenPS

Sharable by multiple unrelated projects Can integrate heterogeneous services and work with existing event

buses– Java, C++, C#, Windows, Linux, Unix, OpenJMS, activeMQ,… Use Web services as “magic bullet”

Internet-scale– Can integrate services across organizations around the world– Support collaboration among brokers from different vendors

XML or simple message as message payload Reliable,

– critical communication foundation Scalable

– Expect high-load in short time and increasing load over time High performance

– Near real-time message delivery

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ImplementationImplementation

32

Filtering Result Summary (FRS)Filtering Result Summary (FRS)

33

Currently, simply use topics and XPath expressions as FRS

Embedded in HTTP header

Other FRS formats are allowed e.g. encrypted

string, unique numbers, etc.

Performance ComparisonPerformance Comparison

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2500 subscriptions (200 unique) for 50 consumers FRS achieved efficient message matching. Future work: improve subscription scalability (FRS may get

too long).

Evaluation on PlanetLabEvaluation on PlanetLab

PlanetLab is a global research network for developing, deploying and accessing planetary-scale services.

Consists of 804 nodes at 391 sites

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http://www.telegeography.com/products/map_internet/index.php

DeploymentDeployment

Deployed to over 300 nodes

Overlay network follows physical network

Created scripts to automatically start, update, and stop services

Latency (LAN)Latency (LAN)

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• Local broker processing dominates (message size: 7079 bytes)

Latency (WAN)

38

• Delay in OpenPS nodes dominates (message size: 7079 bytes)

• Caused by MTU in IP (1.5KB)

Throughput (WAN)

39

POnode

publisher

COnode consumer

bleu

agni

hunk

69.2 ms

OpenPS nodes

Publisher local brokers

(PLBs)

planetlab06.mpi-sws.mpg.de

planetlab05.mpi-sws.mpg.de

Consumer local brokers

(CLB)

exodus

part

linbox3

publisher

publisher

publisherplanetlab02.mpi-sws.mpg.de

planetlab04.mpi-sws.mpg.de

hunk

rogue

rogue

United States Germany

Checkpoint for Receiving rate

Checkpoint for Consumer receiving rate

Checkpoint for Publishing rate

Throughput vs. Thread numbers

Throughput (WAN)Throughput (WAN)

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• Can achieve about 200-300 messages/sec with 600 XPath subscriptions using 7079-byte XML message using 400 threads

• Still have room to improve, e.g. wrapping-up messages

Evaluation Results SummaryEvaluation Results Summary

Latency– In LAN, local broker processing dominates latency.

– In WAN, delay in OpenPS nodes dominates latency due to network latency

Throughput– Used thread pool to compensate latency for higher throughput

– Can achieve about 200-300 msg/s with 600 XPath subscriptions using 7079-byte XML message using 400 threads (From Indiana to Germany)

• Compared to about 3 msg/s using local broker alone

• Compared to about 20 msg/s processing capacity for PL nodes

– Still has room to improve, e.g. wrapping-up messages

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Event Service in Service-oriented Scientific Workflow (LEAD project)

The LEAD ProjectThe LEAD Project

43create infrastructure for better predictions of severe weather

The LEAD ProjectThe LEAD Project

44•$11.25M over 5 years since 2003

Analysis/Assimilation

Quality ControlRetrieval of Unobserved

QuantitiesCreation of Gridded Fields

Prediction/Detection

PCs to Teraflop Systems

Product Generation, Display,

Dissemination

End Users

NWSPrivate Companies

Students

Traditional MethodologyTraditional Methodology

STATIC OBSERVATIONS

Radar Data

Mobile Mesonets

Surface Observations

Upper-Air Balloons

Commercial Aircraft

Geostationary and Polar Orbiting Satellite

Wind Profilers

GPS Satellites

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The Process is Entirely Serialand Static (Pre-Scheduled): No Response to the Weather!

The Process is Entirely Serialand Static (Pre-Scheduled): No Response to the Weather!

Major Paradigm Shift: CASA NETRAD adaptive Major Paradigm Shift: CASA NETRAD adaptive Doppler Radars. Doppler Radars.

Analysis/Assimilation

Quality ControlRetrieval of Unobserved

QuantitiesCreation of Gridded Fields

Prediction/Detection

PCs to Teraflop Systems

Product Generation, Display,

Dissemination

End Users

NWSPrivate Companies

Students

The LEAD Vision: Adaptive CyberinfrastructureThe LEAD Vision: Adaptive Cyberinfrastructure

DYNAMIC OBSERVATIONS

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Models and Algorithms Driving Sensors

The CS challenge: Build cyberinfrastructure services that The CS challenge: Build cyberinfrastructure services that provide adaptability, scalability, availability, useability, and provide adaptability, scalability, availability, useability, and real-time response. real-time response.

The Service ArchitectureThe Service Architecture

48

Use service – to promote a pluggable

framework

– to add new features

– to virtualize access to resources

A Closer look at LEAD Service ArchitectureA Closer look at LEAD Service Architecture

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Data Storage

Application services Compute Engine

User’s Browser

PortalserverPortalserver

DataCatalogservice

DataCatalogservice

MyLEAD UserMetadatacatalog

MyLEAD UserMetadatacatalog

MyLEAD Agent

service

MyLEAD Agent

service DataManagement

Service

DataManagement

Service

WorkflowEngine

WorkflowEngine

Workflow graph

ProvenanceCollection

service

ProvenanceCollection

service

Event Notification Bus

AppfactoryApp

factory

Tied together with Internet-scale event bus.

Example LEAD WorkflowExample LEAD Workflow

Event Service in LEAD WorkflowsEvent Service in LEAD Workflows

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Y. Huang, A. Slominski, et al., "WS-Messenger: A Web Services based Messaging System for Service-Oriented Grid Computing," 6th IEEE International Symposium on

Cluster Computing and the Grid (CCGrid06).

Notification ViewsNotification Views

52

Real TimeMonitor

MyLEAD

Techniques for FirewallsTechniques for Firewalls

53

Problem: How to deliver to event consumers behind the firewalls?

Solution: Use MessageBox Web service

Tools: Subscription Manager Interface Tools: Subscription Manager Interface

Check and delete subscriptions on different brokers from one simple interface

54

Tools: Event Notification Message Viewer Tools: Event Notification Message Viewer

55

Debug Monitor Firewall

ConclusionsConclusions

Extended existing state-of-the-art on Publish/Subscribe systems to Web services and SOA– Mediation among competing WS specifications

– Achieved load scalability, geographic scalability and administrative scalability

Reduced messaging filtering to 1-to-1 (topic-based) and any-to-any (content-based) matching

A layered model for Internet-scale sharable Publish/Subscribe Service– Separation of concerns and economies of scale

Applied to real-world SOA project (LEAD workflow)

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Competing Specification Problem

Expressiveness vs. Scalability problem

Dynamic Workflow OrchestrationEvent Application Layer

Event Transport LayerEvent Distribution Layer

Event Filtering LayerEvent Transformation Layer

Thank You!Thank You!

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