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Chapter 7. Enabling Reliable Messaging

Abstract

Apache CXF supports WS-Reliable Messaging(WS-RM). This chapter explains how to enable and configure WS-RM in Apache CXF.

7.1. Introduction to WS-RM

Overview

WS-ReliableMessaging (WS-RM) is a protocol that ensures the reliable delivery of messages in a distributed environment. It enables messages to be delivered reliably between distributed applications in the presence of software, system, or network failures.
For example, WS-RM can be used to ensure that the correct messages have been delivered across a network exactly once, and in the correct order.

How WS-RM works

WS-RM ensures the reliable delivery of messages between a source and a destination endpoint. The source is the initial sender of the message and the destination is the ultimate receiver, as shown in Figure 7.1, “Web Services Reliable Messaging”.

Figure 7.1. Web Services Reliable Messaging

reliable message exchange
The flow of WS-RM messages can be described as follows:
  1. The RM source sends a CreateSequence protocol message to the RM destination. This contains a reference for the endpoint that receives acknowledgements (the wsrm:AcksTo endpoint).
  2. The RM destination sends a CreateSequenceResponse protocol message back to the RM source. This message contains the sequence ID for the RM sequence session.
  3. The RM source adds an RM Sequence header to each message sent by the application source. This header contains the sequence ID and a unique message ID.
  4. The RM source transmits each message to the RM destination.
  5. The RM destination acknowledges the receipt of the message from the RM source by sending messages that contain the RM SequenceAcknowledgement header.
  6. The RM destination delivers the message to the application destination in an exactly-once-in-order fashion.
  7. The RM source retransmits a message that it has not yet received an acknowledgement.
    The first retransmission attempt is made after a base retransmission interval. Successive retransmission attempts are made, by default, at exponential back-off intervals or, alternatively, at fixed intervals. For more details, see Section 7.4, “Configuring WS-RM”.
This entire process occurs symmetrically for both the request and the response message; that is, in the case of the response message, the server acts as the RM source and the client acts as the RM destination.

WS-RM delivery assurances

WS-RM guarantees reliable message delivery in a distributed environment, regardless of the transport protocol used. Either the source or the destination endpoint logs an error if reliable delivery can not be assured.

Supported specifications

Apache CXF supports the 2005/02 version of the WS-RM specification, which is based on the WS-Addressing 2004/08 specification.

Further information

For detailed information on WS-RM, see the specification at http://specs.xmlsoap.org/ws/2005/02/rm/ws-reliablemessaging.pdf.
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