Sample 9: Introduction to Dynamic Sequences with the Registry

Introduction

This sample demonstrates how you can achieve dynamic behavior of the WSO2 ESB by the use of a registry.

The ESB supports dynamic definitions for sequences, endpoints and configuration resources. Here a Synapse configuration is defined which references a sequence definition specified as a registry key. The registry key resolves to the actual content of the sequence which is loaded dynamically by the ESB at runtime and cached appropriately as per its definition in the registry. Once the cache expires, ESB rechecks the meta information for the definition, reloads the sequence definition if necessary, and caches it again.

Prerequisites

For a list of prerequisites, see Prerequisites to Start the ESB Samples.

Building the sample

The XML configuration for this sample is as follows: 

<definitions xmlns="http://ws.apache.org/ns/synapse">
    <registry provider="org.wso2.carbon.mediation.registry.ESBRegistry">
        <parameter name="root">file:./repository/samples/resources/</parameter>
        <parameter name="cachableDuration">15000</parameter>
    </registry>
    <sequence name="main">
        <sequence key="sequence/dynamic_seq_1.xml"/>
    </sequence>
</definitions>

This configuration file  synapse_sample_9.xml is available in the <ESB_HOME>/repository/samples directory.

To build the sample

1. Start the ESB with the sample 9 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."

2. Start the Axis2 server. For instructions on starting the Axis2 server, see Starting the Axis2 server.

3. Deploy the back-end service SimpleStockQuoteService. For instructions on deploying sample back-end services, see Deploying sample back-end services.

   Now you have a running ESB instance and a back-end service deployed. In the next section, we will send a message to the back-end service through the ESB using a sample client.

Executing the sample

The sample client used here is the Stock Quote Client, which can operate in several modes. For further details on this sample client and its operation modes, see Stock Quote Client.

To execute the sample client

1. Run the following command from the <ESB_HOME>/samples/axis2Client directory.

   ant stockquote -Daddurl=http://localhost:9000/services/SimpleStockQuoteService -Dtrpurl=http://localhost:8280/

2. Execute the client immediately again (within 15 seconds of the last execution) using the above command to make sure that the sequence is not reloaded.
3. Edit the sequence definition in <ESB_HOME>/repository/samples/resources/sequence/dynamic_seq_1.xml, change  the log message to Test Message 2 and execute the client again.
4. Wait for more than 15 seconds since the original caching of the sequence and execute the client again.

Analyzing the output

When you run the client for the first time, ESB fetches the definition of the sequence from the registry and executes its rules. Analyze the debug log output on the ESB console, you will see the following:

[HttpServerWorker-1] DEBUG SequenceMediator - Sequence mediator <dynamic_sequence> :: mediate()
...
[HttpServerWorker-1] INFO  LogMediator - message = *** Test Message 1 ***

When you execute the client immediately again (within 15 seconds of the last execution), you will notice that the sequence is not reloaded.

Once you edit the sequence definition and execute the client again, you will see that the new message is not displayed if you executed the client within 15 seconds of loading the resource for the first time. However, after the elapse of 15 seconds since the original caching of the sequence, you will notice that the new sequence is loaded and executed by Synapse from the following log messag

[HttpServerWorker-1] DEBUG SequenceMediator - Sequence mediator <dynamic_sequence> :: mediate()
...
[HttpServerWorker-1] INFO  LogMediator - message = *** Test Message 2 ***

The cache timeout could be tuned appropriately by configuring the URL registry to suit the environment and the needs.