Reliability on Web Services

Presented by Pat Chan

17/10/2005

Outline

Introduction Reliability Middleware Web Services Possible techniques apply

Multicasting Anycasting Message ordering

Research Direction

Introduction

Web Service is a promoting technique in the internet.

Reliability is an important issue in all middleware communication.

The benefit of interoperability, reusability, and adaptability.

Existing web service model needs to be extended to assure survivability and reliability.

Reliability

"a measure of the success with which the system conforms to some authoritative specification" Guaranteed delivery Duplicate elimination Ordering Crash tolerance State synchronization

Middleware

The glue which connects objects which are distributed across multiple heterogeneous computer systems

An extension of the operating system which provides a transparent communication layer to the applications

A software layer that serves to shield the application of the heterogeneity of the underlying computer platforms and networks

Middleware Goals

Integrate existing components into a distributed system Components may be off-the-shelf Components may have incompatible requirements for hardware and

OS platforms Scalability requires distribution (not centralized or client server).

Resolve heterogeneity Facilitate communication and coordination of distributed

components Build systems distributed across a local area network, the internet

Web Service is the new generation of distributed computing middleware

What are Web Services ?

Self-contained, modular applications built on deployed network infrastructure including XML and HTTP

Use open standards for description (WSDL), discovery (UDDI) and invocation (SOAP)

Web Services

Encapsulated Loosely coupled Contracted

Internet

UDDI

WSDL

HTTP/SOAP

WSDL

Web Services Architecture

SOAPSOAP

HTTP/SMTPHTTP/SMTPXMLXMLTCP/IPTCP/IP

DirectoryDirectory

InspectionInspection

Building Block ModulesBuilding Block Modules

Inter Application ProtocolsInter Application Protocols

ReferralReferral

RoutingRouting

SecuritySecurity

LicenseLicense

EventingEventing TransactionsTransactions

Reliable MessagingReliable Messaging

The InternetThe Internet

DescriptionDescription

……

……

Web Services

Benefits of WS Service-oriented Highly accessible Open specification Easy integration Simplicity

Dynamic Standard

Web Services

Build common infrastructure reducing the barriers of business integration with lower costs and faster speed.

Problems of Web Services

Transaction Atomicity is not provided

Security Insecure Internet transportation

Reliability The internet is inherently unreliable No single underlying “transport protocols”

address all the reliability issues.

Web Services Reliability

There are different proposed approaches for improving the reliability of the web services N-version programming Replication Reliable messaging Message ordering Duplicate elimination

WS-ReliableMessaging

A specification proposed in Feb 2005 Reliable Messaging Model

Application Source

Send Deliver

Application Destination

RM Source RM DestinationTransmit

Acknowledge

Transmit Receive

WS-FTM

Applying n-version model in web service to improve the reliability of web service

Can easily applied to systems with a minimum if the change

FT-SOAP

Fault-tolerant web services

Thema

Byzantine-Fault-Tolerant Middleware for Web Service Applications

Support the multi-tiered requirement of web services Provide standardized web services support for their

own client Combine the BFT with the web services Extend the BASE BFT and the web services toolkits Provide survivable web services

Thema

Web Services Replication

In most of the fault tolerant web service, the basic technique is replication.

As there are number of replicas, each replica must: Get all the request Reach an agreement on the ordering of the

request

Web Services Replication

Web Services

Client

Registry

ServiceProvider

Web Services

Web Services

multicast communication message ordering

Need for Multicasting ?

Maintaining unicast connections is not feasible Infrastructure or services needs to support a “send

to group”

Multicasting

Transmit multiple standard-definition programs simultaneously using a single digital broadcast channel.

Multicasting

Requires coordination and agreement. The aim is for each of a group of processes to

receive copies of the messages sent to the group, often with delivery guarantees.

The guarantees include agreement on the set of messages that every process in

the group should receive and agreement on the deliver ordering across the group

members.

Basic Reliable-Multicasting Schemes

A simple solution to reliable multicasting when all receivers are known and are assumed not to fail

a) Message transmission

b) Reporting feedback

Anycasting

Client requests connection to anycast group Anycast group consists of replicated (equivalent) servers System connects client to any good server

Client

Content Equivlent Servers

Request

??

Anycasting

Anycast identifier specifies a group of equivalent hosts

Requests are sent to best host in the group Advantages for Web Services

Handle large number of client Increase the performance

Message Ordering

Ordered Multicast FIFO order Causal order

Casual order with logical timestamps Casual order with vector timestamps Timestamp compression Casual multicast and consistent cuts

Total order Sync. order

Research Direction

Increase the Reliability of web service Study the Web service failure model Apply the multicasting techniques Apply the anycasting techniques Apply the message ordering techniques Reliable messaging

Research Direction

Client

Registry

ServiceProvider

Web Services

Web Services

Web Services

Replicationmulticast communicationmessage orderinganycasting

Reliable

messaging

Reliable Web Service Paradigm

Client

Registry

Web ServiceWeb Service

Web ServiceWeb Service

Web Service

Web Services GroupRegister WSDL of services

Multicasting Algorithm

Replication Manager

Interface S1 S2

Anycasting Algorithm

Create services

UDDI

WSDL

SOAP / HTTP

Conclusion

Introduction on the Web service Discuss the reliability issue on the the Web services Review number of the current techniques on the

reliability on web services Proposed the possible techniques for improving the

reliability and the performance of web services