Skip to content

Message Dispatcher

This page explains how you can implement a sample scenario of Message Dispatcher EIP using WSO2 Micro Integrator.

Introduction to Message Dispatcher

The Message Dispatcher EIP consumes messages from a single channel and distributes them among performers. It allows multiple consumers on a single channel to coordinate their message processing.

Info

For more information, see the Message Dispatcher documentation.

Message dispatcher

Sample scenario

This sample scenario demonstrates how to distribute messages among performers using the weighted load balance mediator. We have several Axis2 server instances, each considered to be a performer.

The diagram below depicts how to simulate the sample scenario using the WSO2 MI.

Message dispatcher

Before digging into implementation details, let's take a look at the relationship between the sample scenario and the Message Dispatcher EIP by comparing their core components.

Message Dispatcher EIP Message Dispatcher Sample Scenario
Sender Simple Stock Quote Client
Messages Simple Stock Quote Requests
Message Dispatcher Message Endpoint, Load-Balance Endpoint
Performers Simple Stock Quote Server Instance

Synapse configuration of the artifacts

<?xml version="1.0" encoding="UTF-8"?>
<proxy name="StockQuoteProxy" startOnLoad="true" transports="http https" xmlns="http://ws.apache.org/ns/synapse">
    <target>
            <inSequence>
                <call>
                        <endpoint key="LoadBalanceEP"/>
                </call>
                <respond/>
            </inSequence>
            <faultSequence>
                <log level="full">
                        <property name="MESSAGE" value="Executing default &#34;fault&#34; sequence"/>
                        <property name="ERROR_CODE" expression="get-property('ERROR_CODE')"/>
                        <property name="ERROR_MESSAGE" expression="get-property('ERROR_MESSAGE')"/>
                </log>
                <drop/>
            </faultSequence>
    </target>
</proxy>

<?xml version="1.0" encoding="UTF-8"?>
<endpoint name="LoadBalanceEP" xmlns="http://ws.apache.org/ns/synapse">
    <loadbalance algorithm="org.apache.synapse.endpoints.algorithms.WeightedRoundRobin">
            <endpoint>
                <address uri="http://localhost:9000/services/SimpleStockQuoteService/"/>
                <property name="loadbalance.weight" value="1"/>
            </endpoint>
            <endpoint>
                <address uri="http://localhost:9001/services/SimpleStockQuoteService/"/>
                <property name="loadbalance.weight" value="2"/>
            </endpoint>
            <endpoint>
                <address uri="http://localhost:9002/services/SimpleStockQuoteService/"/>
                <property name="loadbalance.weight" value="3"/>
            </endpoint>
    </loadbalance>
</endpoint>

How the implementation works

Let's explore the elements of the configuration:

  • Proxy Service: The StockQuoteProxy proxy service handles incoming requests, forwarding them to a load-balanced set of back-end services.

  • InSequence: Processes the incoming message by invoking the LoadBalanceEP endpoint using the call mediator, then immediately responds to the client using the respond mediator.

  • FaultSequence: Manages errors by logging detailed fault information and dropping the message.

  • Load Balance Endpoint:

    • Endpoint: Specifies multiple back-end service endpoints that will process the requests.
    • LoadBalance: Distributes requests across the endpoints using a Weighted Round-Robin algorithm, where each endpoint has a different weight (1, 2, 3), controlling the proportion of requests each endpoint receives.

Set up the sample scenario

Follow the below instructions to simulate this sample scenario.

  1. Install WSO2 Micro Integrator.

    Info

    Follow the Install the Micro Integrator Runtime documentation for more information.

  2. Launch Visual Studio Code with the Micro Integrator for VS Code extension (MI for VS Code) installed.

    Info

    Follow the Install Micro Integrator for VS Code documentation for a complete installation guide.

  3. Download the backend service.

  4. Extract the downloaded zip file.

  5. Open a terminal, and navigate to the axis2Server/bin/ directory inside the extracted folder.

  6. Execute the following command to start the axis2server with the SimpleStockQuote backend service:

    sh axis2server.sh

    axis2server.bat

  7. Navigate to the MI_HOME/bin/ directory and start the tcpmon application.

  8. In tcpmon application, navigate to Admin tab. Add listeners to ports 9001 and 9002. For each listener set the target hostname to localhost and target port to 9000 in each instance.

  9. Download the artifacts of the sample.

    Download ZIP

  10. Import the artifacts to WSO2 MI.

    Click File -> Open Folder -> Select the extracted ZIP file to import the downloaded ZIP file.

  11. Start the project in the WSO2 MI server.

    For instructions, go to Build and Run Documentation.

  12. Start SoapUI.

    For instructions on downloading and starting, go to SoapUI Getting Started Documentation.

Execute the sample

  1. Repeatedly send several requests using SoapUI (or any other Soap client). 
    POST http://localhost:8290/services/StockQuoteProxy

Accept-Encoding: gzip,deflate
Content-Type: text/xml;charset=UTF-8
SOAPAction: "urn:getQuote"
Connection: Keep-Alive

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ser="http://services.samples" xmlns:xsd="http://services.samples/xsd">
<soapenv:Body>
    <ser:getQuote>
        <ser:request>
            <xsd:symbol>s</xsd:symbol>
        </ser:request>
    </ser:getQuote>
</soapenv:Body>
</soapenv:Envelope>

Analyze the output

Note

In each tcpmon tab and Axis Server console that the requests are distributed among several servers in a weighted manner. Servers running on port 9000, 9001, and 9002 receive the request in that order until the process starts over again in a round-robin manner.