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Competing Consumers

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

Introduction to Competing Consumers

The Competing Consumers EIP relates to multiple consumers that compete with each other to receive a request from a given Point-to-Point Channel. In this pattern, requests are handled and delegated similar to how messages are handled in the Point-to-Point channel using the round-robin algorithm.

Info

For more information, see the Competing Consumers.

Competing consumers

Sample scenario

In this sample scenario, each Axis2 server instance acts as a consumer waiting for a specific message. When the client sends a message to WSO2 MI, it diverts the request based on the round-robin algorithm among the consumers. This way, the consumers receive a request message adhering to the conditions of the algorithm.

An alternative implementation to the Competing Consumers EIP is to use a Content-Based Router and route messages to different receivers based on the content of a message.

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

Competing consumers

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

Competing Consumers EIP Competing Consumers Sample Scenario
Sender Simple Stock Quote Client
Messages Simple Stock Quote Requests with Load-Balance Endpoint
Consumer/Receiver Simple Stock Quote Server Instances

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.RoundRobin">
      <endpoint>
            <address uri="http://localhost:9000/services/SimpleStockQuoteService"></address>
      </endpoint>
      <endpoint>
            <address uri="http://localhost:9001/services/SimpleStockQuoteService"></address>
      </endpoint>
      <endpoint>
            <address uri="http://localhost:9002/services/SimpleStockQuoteService"></address>
      </endpoint>
   </loadbalance>
</endpoint>

How the implementation works

Let's explore the elements of the configuration:

  • Proxy Service: The StockQuoteProxy proxy service receives requests and forwards them to the appropriate back-end services using a load-balancing mechanism.

  • InSequence: Directs the incoming message to the LoadBalanceEP endpoint using the call mediator, and then immediately responds to the client with the respond mediator.

  • FaultSequence: Handles errors by logging the full details of any faults and dropping the message.

  • Load Balance Endpoint:

    • Endpoint: Defines a group of back-end service endpoints that handle the requests.
    • LoadBalance: Distributes incoming requests across multiple endpoints using the Round-Robin algorithm, ensuring an even distribution of traffic among the services at http://localhost:9000, http://localhost:9001, and http://localhost:9002.

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, refer to Build and Run.

  12. Start SoapUI.

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

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>IBM</xsd:symbol>
        </ser:request>
    </ser:getQuote>
</soapenv:Body>
</soapenv:Envelope>

Analyze the output

Note

In tcpmon tabs and Axis Server console that the requests are distributed among several servers. Each server is acting as a competing consumer.