Sample 54: Session affinity load balancing between 3 endpoints

Objective: Demonstrate the load balancing with session affinity using client initiated sessions

<definitions xmlns="http://ws.apache.org/ns/synapse">
    <sequence name="main" onError="errorHandler">
        <in>
            <send>
                <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/LBService1">
                                <enableAddressing/>
                            </address>
                        </endpoint>
                        <endpoint>
                            <address uri="http://localhost:9002/services/LBService1">
                                <enableAddressing/>
                            </address>
                        </endpoint>
                        <endpoint>
                            <address uri="http://localhost:9003/services/LBService1">
                                <enableAddressing/>
                            </address>
                        </endpoint>
                    </loadbalance>
                </endpoint>
            </send><drop/>
        </in>
        <out>
            <!-- Send the messages where they have been sent (i.e. implicit To EPR) -->
            <send/>
        </out>
    </sequence>
    <sequence name="errorHandler">
        <makefault>
            <code value="tns:Receiver" xmlns:tns="http://www.w3.org/2003/05/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>
</definitions>

Prerequisites:

Start ESB with sample configuration 54: i.e. wso2esb-samples.sh -sn 54
Deploy the LoadbalanceFailoverService and start three instances of the sample Axis2 server as in sample 52.

Above configuration is same as the load balancing configuration in sample 52, except that 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 to with each request. In this sample session type, client adds a SOAP header named ClientID containing the identifier of the client. ESB binds this ID with a server on the first request and sends all seccessive requests containing that ID to the same server. Now switch to samples/axis2Client directory and run the client using the following command to check this in action.

ant loadbalancefailover -Dmode=session

In the session mode, client continuously sends requests with three diferent client (session) IDs. One ID is selected among these three IDs for each request randomly. Then client prints the session ID with the responded server for each request. Client output for the first 10 requests are shown below.

[java] Request: 1 Session number: 1 Response from server: MyServer3
[java] Request: 2 Session number: 2 Response from server: MyServer2
[java] Request: 3 Session number: 0 Response from server: MyServer1
[java] Request: 4 Session number: 2 Response from server: MyServer2
[java] Request: 5 Session number: 1 Response from server: MyServer3
[java] Request: 6 Session number: 2 Response from server: MyServer2
[java] Request: 7 Session number: 2 Response from server: MyServer2
[java] Request: 8 Session number: 1 Response from server: MyServer3
[java] Request: 9 Session number: 0 Response from server: MyServer1
[java] Request: 10 Session number: 0 Response from server: MyServer1
...

You can see that session number 0 is always directed to the server named MyServer1. That means session number 0 is bound to MyServer1. Similarly session 1 and 2 are bound to MyServer3 and MyServer2 respectively.