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Message Bus

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

Introduction to Message Bus

The Message Bus EIP enables separate applications to work together in a decoupled manner so that applications can be easily added or removed without affecting each other. This approach makes maintenance and testing smoother since editing or removing an application will not affect the functionality of any other application.

Info

For more information, refer to the Message Bus documentation.

Message bus solution

Sample scenario

This sample scenario demonstrates how application logic is layered, and how each component of the application logic is separated as a mediator, allowing message processing to be executed in a decoupled manner. The mediation process is explained in the Mediation Sequences documentation.

Synapse configuration of the artifacts

<?xml version="1.0" encoding="UTF-8"?>
<proxy name="MessageBusProxy" startOnLoad="true" transports="http https" xmlns="http://ws.apache.org/ns/synapse">
    <target>
        <inSequence>
            <filter regex=".*/StockQuote.*" source="get-property('To')">
                <then>
                    <call>
                        <endpoint key="SimpleStockQuoteServiceEp"/>
                    </call>
                </then>
                <else>
                    <drop/>
                </else>
            </filter>
            <respond/>
        </inSequence>
    </target>
</proxy>

<?xml version="1.0" encoding="UTF-8"?>
<endpoint name="SimpleStockQuoteServiceEp" xmlns="http://ws.apache.org/ns/synapse">
    <address uri="http://localhost:9000/services/SimpleStockQuoteService">
        <suspendOnFailure>
            <initialDuration>-1</initialDuration>
            <progressionFactor>1</progressionFactor>
        </suspendOnFailure>
        <markForSuspension>
            <retriesBeforeSuspension>0</retriesBeforeSuspension>
        </markForSuspension>
    </address>
</endpoint>

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. Download the artifacts of the sample.

    Download ZIP

  8. Import the artifacts to WSO2 MI.

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

  9. Start the project in the WSO2 MI server.

    For instructions, go to Build and Run Documentation.

Execute the sample

Send the following request to the service.

POST http://localhost:8290/services/MessageBusProxy/StockQuote
Content-type: text/xml;charset=UTF-8
soapAction: urn:getQuote

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

Analyze the output

According to the configuration above, the service routes an incoming message to a backend server if the conditions specified in the filter section are met. Notice how the application's logic is decoupled. It uses one component for filtering, and another to send a message to the endpoint. If you were to decide to remove the filtering step, you could remove the filter mediator segment from the XML without affecting the application's logic for sending the message to the backend server.