Reliability on Web Services

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Reliability on Web Services

• Presented by Pat Chan
• 17/10/2005

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Outline

• Introduction
• Reliability
• Middleware
• Web Services
• Possible techniques apply
• Multicasting
• Anycasting
• Message ordering
• Research Direction

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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.

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Reliability

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

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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

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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

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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)

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Web Services
UDDI

• Encapsulated
• Loosely coupled
• Contracted

Internet
WSDL
WSDL
HTTP/SOAP
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Web Services Architecture
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Web Services
Build common infrastructure reducing the barriers
of business integration with lower costs and
faster speed.

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

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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.

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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

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WS-ReliableMessaging

• A specification proposed in Feb 2005
• Reliable Messaging Model

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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

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FT-SOAP

• Fault-tolerant web services

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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

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Thema
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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

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Web Services Replication
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Need for Multicasting ?

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

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Multicasting

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

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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.

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Basic Reliable-Multicasting Schemes

• A simple solution to reliable multicasting when
  all receivers are known and are assumed not to
  fail
• Message transmission
• Reporting feedback

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Anycasting

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

?
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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

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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

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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

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Research Direction
Reliable messaging
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Reliable Web Service Paradigm
UDDI
Registry
Web Services Group
Register WSDL of services
Client
WSDL
Create services
SOAP / HTTP
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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