WS-Reliability Pattern

1
WS-Reliability Pattern

• Ingrid Buckley
• Dept. of Computer Science and Engineering
  Florida Atlantic UniversityBoca Raton, FL, USA
• July 24, 2008.

2
Agenda

• Motivation
• Objective
• Introduction
• WS-Reliability Pattern
• Questions
• Recommendations

3
Motivation

• SOAP over HTTP is not sufficient when an
  application-level messaging protocol must also
  guarantee some level of reliability and security.
• Providing a convenient means to achieve reliable
  messaging in web services.
• To write a pattern that is helpful to programmers
  to aid them in designing and implementing
  WS-Reliability in a web service application.

4
Objective

• To write a pattern that describes the
  WS-Reliability
• Standard.

5
Introduction

• WS-Reliability is a SOAP-based (SOAP 1.1 and
  SOAP 1.2 Part 1) specification that fulfills
  reliable messaging requirements critical to some
  applications of Web Services.
• The WS-Reliability Standard has been defined by
  OASIS and has borrowed from the ebXML Message
  Service Specification 2.0 technology.
• SOAP over HTTP is not sufficient when an
  application-level messaging protocol must also
  guarantee some level of reliability and security.
  This specification defines reliability in the
  context of current Web Services standards.

6
Introduction

• The WS-Reliability standard utilizes quality of
  service (QOS) contracts, and uses conditions
  attached to the invocation of a set of
  operations namely deliver, submit, respond and
  notifyOas04.
• This specification has been designed for use in
  combination with other complementary protocols
• ebXML
• SOAP
• Message Security
• WS-I Basic Profile 1.1

7
WS-Reliability Pattern

• WS-Reliability
• Intent
• WS-Reliability ensures that a notification is
  always sent in response to a failure, it also
  fulfils message ordering and duplicate
  elimination and guaranteed delivery, whenever
  messages are sent from one entity to another.
  This is done using Sending and Receiving
  Messaging Processors that send, receive, orders
  and eliminate duplicate messages.
• Context
• Due to the widespread use of the internet by
  many companies conducting business transactions,
  it becomes necessary to ensure reliable
  communication between them. It is important that
  messages dont get lost or delayed, especially in
  time-critical transactions.

8
WS-Reliability Pattern

• Problem
• Some applications need to have reliable
  messaging in order to fulfill their business
  operations effectively and successfully. Many
  companies offer services to consumers across the
  internet, which give rise to bandwidth,
  availability and reliability issues which can
  negatively affect the services being offered.
• How do we ensure that messages which are
  sent are acknowledged, delivered, sent in order,
  and without any duplication?
• The solution to this problem is affected by the
  following forces
• Network traffic across the internet affects the
  time it takes a message to reach a recipient
  this may increase the delay time for the
  messages.
• The receiving or sending parties may not be
  available and messages may not be sent or
  received.
• The Internet connection speed used by both
  receiving and the sending party, this affects how
  quickly messages are sent and received.
• The Internet may crash causing messages en route
  to either the sender or receiver to get lost.

9
WS-Reliability Pattern

• Solution
• Use a protocol that performs guaranteed
  message delivery with acknowledgement of failure,
  ordering and duplicate elimination.
• This can be achieved by first having an
  enforced agreement (a contract) between the
  sending and receiving parties, and the use of a
  sending and receiving messaging processor that
  sends, delivers, orders and eliminate duplicate
  messages.
• Structure
• Figure 1 describes the structure of this
  pattern.

10
Figure 1 Class Diagram for the WS-Reliability
pattern
11
WS-Reliability Pattern

• Structure
• A contract is defined which enforces the
  quality of service expected between the sending
  and receiving RMP as well as the terms of the
  relationship between the producer and the
  consumer.
• The contract includes a specification of the
  expected quality of service (QoS), which
  determines the quality of messaging service to
  the communicating parties, and also includes the
  features which define the operations and rules
  which are expected.
• The ReliableMessagingProcessor (RMP) Oas04
  handles messages that are sent between a producer
  and a consumer and performs reliable messaging as
  outlined in the contract in
• the form of requirements such as guaranteed
  delivery, duplicate message elimination, and
  message ordering.

12
WS-Reliability Pattern

• Structure
• The Producer creates messages and sends them
  to the Sending RMP. The Consumer consumes
  messages that have been processed by the
  Receiving RMP. A Message can be Group Message or
  an Individual Message which contains a
  ltwsrmRequestgt header block with varying
  attributes depending on the message used. The
  MessageExchangeProtocol defines different modes
  of response which can be sent from the Consumer
  to the Receiving RMP in response to a previously
  received message.

13
WS-Reliability Pattern

• Dynamics
• We described the dynamics aspects of the
  WS-Reliability using
• a sequence diagram for the use case
  Sending a reliable
• message.
• Sending a reliable message (Figure 2)
• Summary A producer wishes to send a
  message to a consumer.
• Actors Producer, Consumer.
• Precondition The producer and the
  consumer must have a
• defined contract/agreement prior to
  communicating with each
• other.

14
WS-Reliability Pattern

• Dynamics
• Description
• The producer creates and sends one or more
  messages (group messages) as required to the
  Sending RMP for it to submit to a consumer.
• The Receiving-RMP accepts the message from the
  Sending RMP and forwards it to the consumer.
• The consumer acknowledges reception of the
  message by sending a response back to the
  Receiving RMP.
• This response is sent to the sending-RMP who
  notifies the producer of the response sent from
  the consumer.
• Post-condition An acknowledgement must be
  sent to the producer every time a message failure
  occurs.

15
Figure 2 Sequence Diagram illustrating the
sending and receiving of a Reliable message
16
WS-Reliability Pattern

• Implementation
• To implement the WS-Reliability, the
  following is
• required
• Have a mechanism that can enforce a contract
  defined by both communicating parties.
• The RMP processor has to be a SOAP processor,
  which
• is a processor which specializes in
  handling soap
• messages, and any other infrastructure
  capable of
• performing the reliable messaging
  requirements discussed
• earlier.

17
WS-Reliability Pattern

• Consequences
• The WS- Reliable pattern presents the
  following advantages
• Messages sent between companies can be governed
  by means of the protocol which ensure delivery by
  an acknowledgment, ordering and duplicate
  elimination of messages.
• Enterprises are able to yield a higher degree of
  reliability for communication sent through the
  internet, because both parties confirm reception
  by some repsonse each time they communicate via a
  message.
• Quality of service can be maintained between
  businesses. Policies can be attached to the
  contracts that govern the modus operandi agreed
  to by all communicating parties.
• This protocol supports several complementary
  protocols such as SOAP 1.1/1.2, thus leveraging
  the use of standards that can be adopted by
  companies. By using more standards this helps an
  enterprise to conform to current industry
  protocols and may help them to partner with other
  companies that use the same standards.
• The messaging components can be implemented in
  different ways, as an application, a queuing or
  logging system, or a database or soap node. In
  addition they can be designed using different
  frameworks such as .NET, and JAVA.

18
WS-Reliability Pattern

• Consequences
• The pattern also has some possible
  liabilities
• Depending on how the messaging components are
  implemented, there could result, a longer
  turnaround time to acknowledge a message.
• The framework used to implement and design the
  message components affect the efficiency of the
  messaging features discussed earlier, because
  some frameworks are more powerful than others.

19
WS-Reliability Pattern

• Known Uses
• This pattern is utilized in Reliable
  Messaging for Grid Services (RM4GS) Fuj04, this
  is middleware open source application produced by
  Fujitsu Limited, Hitachi, Ltd., and NEC
  Corporation.
• Related patterns
• The WS-Reliability sends Acknowledgements to
  confirm receipt of a message as apart of its
  solution, this can be done using the
  Acknowledgment pattern in Buc08.

20
References

• Buc08 I. Buckley, E.B Fernandez, A Survey of
  Fault Tolerance Patterns,
• Department of Computer Science and Engineering
  Florida Atlantic
• University, 2007.
• Oas04 OASIS, Web Services Reliable Messaging
  TC WS-
• Reliability 1.1,http//docs.oasis-open.org/wsrm/w
  reliability/v1.1/wsrm-
• ws_reliability-1.1-spec-os.pdf, 2004.
• For08 Forum Systems Inc., Introduction to SOA
  Gateways Best
• Practices. Benefits Requirements, May, 2008.
• Fuj04 Fujitsu Limited, Hitachi, Ltd., NEC
  Corporation, RM4GS Overview,
• http//xml.coverpages.org/RM4GS-Overview20040305.
  pdf, March, 2004

21
Recommendations and Questions

• Feedback