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 SOAP HTTP/SMTPXMLTCP/IP Directory Inspection Building Block Modules Building Block Modules Inter Application Protocols Referral Routing Security License EventingTransactions Reliable Messaging The Internet Description … …

Web Services  Benefits of WS Service-oriented Highly accessible Open specification Easy integration Simplicity DynamicStandard 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 Destination Transmit Acknowledge TransmitReceive

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 Service Provider 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 ?

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 Service Provider Web Services Replication  multicast communication  message ordering  anycasting Reliable messaging

Reliable Web Service Paradigm Client Registry Web Service Web Services Group Register 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