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Using the Load Balance Endpoint¶

Session Affinity Load Balancing between Three Endpoints

This sample demonstrates how the Micro Integrator can handle load balancing with session affinity using simple client sessions. Here the session type is specified as simpleClientSession . This is a client initiated session, which means that the client generates the session identifier and sends it with each request. In this sample session type, the client adds a SOAP header named ClientID containing the identifier of the client. The MI binds this ID with a server on the first request and sends all successive requests containing that ID to the same server.

Synapse configuration¶

Following is a sample REST API configuration that we can used to implement this scenario.

Proxy Service

<proxy name="LoadBalanceProxy" startOnLoad="true" transports="http https" xmlns="http://ws.apache.org/ns/synapse">
   <target>
       <inSequence>
            <header name="Action" value="urn:placeOrder"/>
            <call>
                <endpoint>
                    <!-- specify the session as the simple client session provided by Synapse for
                    testing purpose -->
                    <session type="simpleClientSession"/>

                    <loadbalance>
                        <endpoint>
                            <address uri="http://localhost:9001/services/SimpleStockQuoteService">
                                <enableAddressing/>
                            </address>
                        </endpoint>
                        <endpoint>
                            <address uri="http://localhost:9002/services/SimpleStockQuoteService">
                                <enableAddressing/>
                            </address>
                        </endpoint>
                        <endpoint>
                            <address uri="http://localhost:9003/services/SimpleStockQuoteService">
                                <enableAddressing/>
                            </address>
                        </endpoint>
                    </loadbalance>
                </endpoint>
            </call>
            <respond/>
       </inSequence>
       <outSequence>
            <send/>
       </outSequence>
       <faultSequence>
            <sequence key="errorHandler"/>
       </faultSequence>
   </target>
</proxy>

Sequence

<sequence name="errorHandler"> 
    <makefault version="soap11">
        <code value="soap11Env:VersionMismatch" xmlns:soap11Env="http://schemas.xmlsoap.org/soap/envelope/"/>
        <reason value="COULDN'T SEND THE MESSAGE TO THE SERVER."/>
    </makefault>

    <header name="To" action="remove"/>
    <property name="RESPONSE" value="true"/>
    <send/>
</sequence>

Build and run¶

Create the artifacts:

Set up ESB Integration Studio.
Create an integration project with an ESB Configs module and an Composite Exporter.
Create the Proxy and the Sequence with the configurations given above.
Deploy the artifacts in your Micro Integrator.

Set up the back-end service:

Download the back-end service.
Extract the downloaded zip file.
Open a terminal, navigate to the axis2Server/bin/ directory inside the extracted folder.
Execute the following command to start the axis2server with the SimpleStockQuote back-end service:
On MacOS/Linux/CentOS
```
sh axis2server.sh
```
On Windows
```
axis2server.bat
```
Open the tcpmon application, which is in MI_TOOLING_HOME/Contents/Eclipse/runtime/microesb/bin/ (in MacOS) or MI_TOOLING_HOME/runtime/microesb/bin (in Windows/Linux) directory.
Configure tcpmon to listen to ports 9001, 9002, and 9003 and set the target hostname to localhost and target port to 9000 in each instance.

Invoking the proxy service:

Send the following request 3 or more times. Make sure to include a simpleClientSession to the header.

POST http://localhost:8290/services/LoadBalanceProxy HTTP/1.1
Content-Type: text/xml;charset=UTF-8
simpleClientSession: 123

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
   <soapenv:Header/>
   <soapenv:Body>
   <m0:placeOrder xmlns:m0="http://services.samples">
            <m0:order>
                <m0:price>172.23182849731984</m0:price>
                <m0:quantity>18398</m0:quantity>
                <m0:symbol>IBM</m0:symbol>
            </m0:order>
        </m0:placeOrder>
   </soapenv:Body>
</soapenv:Envelope>

Analyzing the output:

When inspecting the tcpmon, you will see that each listener has received a request (If you have only sent 3 requests, otherwise more than 1). This is because, when multiple requests are sent with the same session ID, they are distributed across the three endpoints in a round robin manner.

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