This sample demonstrates how the ESB can handle session aware load balancing between failover endpoints.
The configuration in this sample also uses the session type
simpleClientSession to bind session ID values to servers as in sample 54. The difference in this sample is that failover endpoints are specified as child endpoints of the load balance endpoint. Therefore, sessions are bound to the failover endpoints. The session specific data maintained in endpoint servers are replicated among the failover endpoints using a clustering mechanism. Therefore, if one endpoint bound to a session fails, successive requests for that session will be directed to the next endpoint in that failover group.
For a list of prerequisites, see Prerequisites to Start the ESB Samples.
Building the sample
The XML configuration for this sample is as follows:
This configuration file
synapse_sample_55.xml is available in the
To build the sample
Start the ESB with the sample 55 configuration. For instructions on starting a sample ESB configuration, see Starting the ESB with a sample configuration.
The operation log keeps running until the server starts, which usually takes several seconds. Wait until the server has fully booted up and displays a message similar to "WSO2 Carbon started in n seconds."
Start four instances of the sample Axis2 server on HTTP ports 9001, 9002, 9003 and 9004 respectively and give unique names to each server. For instructions on starting the Axis2 server, see Starting the Axis2 server.
Deploy the back-end service LoadbalanceFailoverService. For instructions on deploying sample back-end services, see Deploying sample back-end services.
Executing the sample
The sample client used here is the Load Balance and Failover Client.
To execute the sample client
Run the following command from the
- While the client is running, stop the server named MyServer1.
Analyzing the output
When the client is run, you will see the following output on the client console:
By analysing the above output, you will see that the session 0 and session 1 are always directed to MyServer1 whereas session 2 is always directed to MyServer3. You will notice that none of the requests are directed to MyServer2 and MyServer4. This is because MyServer2 and MyServer4 are kept as backup servers by the failover endpoints.
When MyServer1 is stopped while running the sample, you will see that all successive requests for session 0 are directed to MyServer2, which is the backup server for MyServer1's failover group.
The output on the client console will be as follows:
By analysing the above output, you will see that all requests for session 0 are directed to MyServer2 after the request 534. Therefore, you can come to the conclusion that MyServer1 was stopped after request 534.