Apache Synapse

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## Sample 57: Dynamic Load Balancing Between 3 Nodes

<definitions xmlns="http://ws.apache.org/ns/synapse"> <sequence name="main" onError="errorHandler"> <in> <send> <endpoint name="dynamicLB"> <dynamicLoadbalance failover="true" algorithm="org.apache.synapse.endpoints.algorithms.RoundRobin"> <membershipHandler class="org.apache.synapse.core.axis2.Axis2LoadBalanceMembershipHandler"> <property name="applicationDomain" value="apache.axis2.app.domain"/> </membershipHandler> </dynamicLoadbalance> </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 response="true"> <code xmlns:tns="http://www.w3.org/2003/05/soap-envelope" value="tns:Receiver"/> <reason value="COULDN'T SEND THE MESSAGE TO THE SERVER."/> </makefault> <send/> </sequence> </definitions>

### Objective

Demonstrate the ability of Synapse to perform dynamic load balancing. In dynamic load balancing, nodes can be added and removed from the pool dynamically.

### Pre-requisites

- Deploy the LoadbalanceFailoverService by switching to samples/axis2Server/src/LoadbalanceFailoverService directory and running 'ant'.
- Enable clustering for the sample Axis2 server. Edit the axis2.xml file at samples/axis2Server/repository/conf directory and set the 'enable' attribute on the 'clustering' element to 'true'. Specify the IP address of the machine as the values of 'mcastBindAddress' and 'localMemberHost' parameters.
- Enable clustering for Synapse by editing repository/conf/axis2.xml file. This should be done by setting the 'enable' attribute of the 'clustering' element to 'true'. Also provide the IP address of your machine as the values of the 'mcastBindAddress' and 'localMemberHost' parameters. In addition also set the 'enable' attribute on 'groupManagement' element to 'true'.
- Start Synapse using the configuration numbered 57 (repository/conf/sample/synapse_sample_57.xml)
  Unix/Linux: sh synapse.sh -sample 57
  Windows: synapse.bat -sample 57
- Start 3 instances of the sample Axis2 server as follows.
  ./axis2server.sh -http 9001 -https 9005 -name MyServer1
  ./axis2server.sh -http 9002 -https 9006 -name MyServer2
  ./axis2server.sh -http 9003 -https 9007 -name MyServer3

### Executing the Client

Note that the Synapse configuration does not define any concrete addresses or URLs as targets. They are discovered dynamically by the dynamic load balance endpoint. To test this feature start the load balance and failover client using the following command:

ant loadbalancefailover -Di=100

This client sends 100 requests to the LoadbalanceFailoverService through Synapse. Synapse will distribute the load among the three nodes we have started in round-robin manner. LoadbalanceFailoverService appends the name of the server to the response, so that client can determine which server has processed the message. If you examine the console output of the client, you can see that requests are processed by three servers as follows:

[java] Request: 1 ==> Response from server: MyServer1 [java] Request: 2 ==> Response from server: MyServer2 [java] Request: 3 ==> Response from server: MyServer3 [java] Request: 4 ==> Response from server: MyServer1 [java] Request: 5 ==> Response from server: MyServer2 [java] Request: 6 ==> Response from server: MyServer3 [java] Request: 7 ==> Response from server: MyServer1 ...

Now run the client without the -Di=100 parameter, to send infinite requests. While running the client shutdown the server named MyServer1. You can observe that requests are only distributed among MyServer2 and MyServer3 after shutting down MyServer1. Console output before and after shutting down MyServer1 is listed below (MyServer1 was shutdown after request 63):

... [java] Request: 61 ==> Response from server: MyServer1 [java] Request: 62 ==> Response from server: MyServer2 [java] Request: 63 ==> Response from server: MyServer3 [java] Request: 64 ==> Response from server: MyServer2 [java] Request: 65 ==> Response from server: MyServer3 [java] Request: 66 ==> Response from server: MyServer2 [java] Request: 67 ==> Response from server: MyServer3 ...

Now restart MyServer1. You can observe that requests will be again sent to all three servers. If you start a new Axis2 instance (say MyServer4) that will also be added to the load balance pool dynamically.

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