Sample 53: Failover sending among 3 endpoints

Objective: Demonstrate the failover sending

<definitions xmlns="http://ws.apache.org/ns/synapse">
    <sequence name="main" onError="errorHandler">
        <in>
            <send>
                <endpoint>
                    <failover>
                        <endpoint>
                            <address uri="http://localhost:9001/services/LBService1">
                                <enableAddressing/>
                                <suspendDurationOnFailure>60</suspendDurationOnFailure>
                            </address>
                        </endpoint>
                        <endpoint>
                            <address uri="http://localhost:9002/services/LBService1">
                                <enableAddressing/>
                                <suspendDurationOnFailure>60</suspendDurationOnFailure>
                            </address>
                        </endpoint>
                        <endpoint>
                            <address uri="http://localhost:9003/services/LBService1">
                                <enableAddressing/>
                                <suspendDurationOnFailure>60</suspendDurationOnFailure>
                            </address>
                        </endpoint>
                    </failover>
                </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 53: wso2esb-samples.sh -sn 53
Deploy the LoadbalanceFailoverService and start three instances of sample Axis2 server as mentioned in sample 52.

Above configuration sends messages with the failover behavior. Initially the server at port 9001 is treated as primary and other two are treated as back ups. Messages are always directed only to the primary server. If the primary server has failed, next listed server is selected as the primary. Thus, messages are sent successfully as long as there is at least one active server. To test this, run the loadbalancefailover client to send infinite requests as follows:

ant loadbalancefailover

You can see that all requests are processed by MyServer1. Now shutdown MyServer1 and inspect the console output of the client. You will observe that all subsequent requests are processed by MyServer2.

The console output with MyServer1 shutdown after request 127 is listed below:

...
[java] Request: 125 ==> Response from server: MyServer1
[java] Request: 126 ==> Response from server: MyServer1
[java] Request: 127 ==> Response from server: MyServer1
[java] Request: 128 ==> Response from server: MyServer2
[java] Request: 129 ==> Response from server: MyServer2
[java] Request: 130 ==> Response from server: MyServer2
...

You can keep on shutting down servers like this. Client will get a response till you shutdown all listed servers. Once all servers are shutdown, the error sequence is activated and a fault message is sent to the client as follows.

[java] COULDN'T SEND THE MESSAGE TO THE SERVER.

Once a server is detected as failed, it will be added to the active servers list again after 60 seconds (specified in <suspendDurationOnFailure> in the configuration). Therefore, if you have restarted any of the stopped servers and have shutdown all other servers, messages will be directed to the newly started server.