Guaranteed Delivery with Failover Message Store and Scheduled Failover Message Forwarding Processor

The ESB profile of WSO2 EI ensures guaranteed delivery with the failover message store and scheduled failover message forwarding processor.

The topics in the following section describe how you can setup guaranteed message delivery with failover configurations.

Example Scenario

The following diagram illustrates a scenario where a failover message store and scheduled failover message forwarding processor is used to ensure guaranteed delivery:

In this scenario, the original message store fails due to either network failure, message store crash or system shutdown for maintenance, and the failover message store is used as the solution for the original message store failure. So now the store mediator sends messages to the failover message store. Then, when the original message store is available again, the messages that were sent to the failover message store need to be forwarded to the original message store. The scheduled failover message forwarding processor is used for this purpose. The scheduled failover message forwarding processor is almost the same as the scheduled message forwarding processor, the only difference is that the scheduled message forwarding processor forwards messages to a defined endpoint, whereas the scheduled failover message forwarding processor forwards messages to the original message store that the message was supposed to be temporarily stored.

Setting up the example scenario

Create the failover message store

In this example an in-memory message store is used to create the failover message store. If you have a cluster setup, it will not be possible to use an in-memory message store since it is not possible to share in-memory stores among nodes in a cluster. This step does not involve any special configuration.

<messageStore name="failover"/>

Create the original message store

In this example a JMS message store is used to create the original message store. When creating the original message store, you need to enable guaranteed delivery on the producer side. To do this, set the following parameters in the message store configuration:

<parameter name="store.failover.message.store.name">failover</parameter>
<parameter name="store.producer.guaranteed.delivery.enable">true</parameter>

Following is the message store configuration used in this example:

 <messageStore  
     class="org.apache.synapse.message.store.impl.jms.JmsStore" name="Orginal">  
     <parameter name="store.failover.message.store.name">failover</parameter>  
     <parameter name="store.producer.guaranteed.delivery.enable">true</parameter>  
     <parameter name="java.naming.factory.initial">org.apache.activemq.jndi.ActiveMQInitialContextFactory</parameter>  
     <parameter name="java.naming.provider.url">tcp://localhost:61616</parameter>  
     <parameter name="store.jms.JMSSpecVersion">1.1</parameter>  
   </messageStore>

Create the proxy service to send messages to the original message store via the store mediator

Following is the proxy service used in this example:

<proxy name="Proxy1" transports="https http" startOnLoad="true" trace="disable">    
  <target>  
    <inSequence>  
     <property name="FORCE_SC_ACCEPTED" value="true" scope="axis2"/>  
     <property name="OUT_ONLY" value="true"/>  
     <log level="full"/>  
     <store messageStore="Orginal"/>  
    </inSequence>  
  </target>  
 </proxy>

Define the endpoint for the scheduled message forwarding processor

In this example, the SimpleStockquate service is used as the back-end service. Follow the instructions below to define the address endpoint.

Log in to the Management Console of the ESB profile.
Click Main -> Service Bus -> Endpoints -> Add Endpoint -> Address Endpoint.

Enter the following details as shown below.

<endpoint name="SimpleStockQuoteService">  
  <address uri="http://127.0.0.1:9000/services/SimpleStockQuoteService"/>  
</endpoint>

Click Save & Close.

Create a scheduled message forwarding processor to forward messages to the defined endpoint

Following is the scheduled message forwarding processor configuration used in this example:

<messageProcessor name="ForwardMessageProcessor" class="org.apache.synapse.message.processor.impl.forwarder.ScheduledMessageForwardingProcessor" targetEndpoint="SimpleStockQuoteService" messageStore="Orginal" xmlns="http://ws.apache.org/ns/synapse">
   <parameter name="interval">1000</parameter>
   <parameter name="client.retry.interval">1000</parameter>
   <parameter name="max.delivery.attempts">4</parameter>
   <parameter name="is.active">true</parameter>
   <parameter name="max.delivery.drop">Disabled</parameter>
   <parameter name="member.count">1</parameter>
</messageProcessor>

For more information, see Scheduled Message Forwarding Processor.

Create a scheduled failover message forwarding processor

When creating the scheduled failover message forwarding processor, you need to specify the following two mandatory parameters that are important in the failover scenario.

Source Message Store
Target Message Store

The scheduled failover message forwarding processor sends messages from the failover store to the original store when it is available in the failover scenario. In this configuration, the source message store should be the failover message store and target message store should be the original message store.

Following is the scheduled failover message forwarding processor configuration used in this example:

<messageProcessor name="FailoverMessageProcessor" class="org.apache.synapse.message.processor.impl.failover.FailoverScheduledMessageForwardingProcessor" messageStore="failover" xmlns="http://ws.apache.org/ns/synapse">
   <parameter name="interval">1000</parameter>
   <parameter name="client.retry.interval">60000</parameter>
   <parameter name="max.delivery.attempts">1000</parameter>
   <parameter name="is.active">true</parameter>
   <parameter name="max.delivery.drop">Disabled</parameter>
   <parameter name="member.count">1</parameter>
   <parameter name="message.target.store.name">Orginal</parameter>
</messageProcessor>

Send the request to the proxy service

Navigate to the <EI_HOME>/samples/axis2Server/src/SimpleStockQuoteService directory, and run ant to build and deploy the sample service in the Axis2 server.
Navigate to the <EI_HOME>/samples/axis2client directory, and execute the following command to invoke the proxy service:
```
ant stockquote -Daddurl=http://localhost:8280/services/Proxy1 -Dmode=placeorder  
```
You will see the following message on the Axis2 server console:
```
SimpleStockQuoteService :: Accepted order for : 7482 stocks of IBM at $ 169.27205579038733  
```

Testing the example scenario

To test the failover scenario, shut down the JMS broker(i.e., the original message store) and send a few messages to the proxy service.

You will see that the messages are not sent to the back-end since the original message store is not available. You will also see that the messages are stored in the failover message store.

If you analyze the the ESB profile log, you will see the failover message processor trying to forward messages to the original message store periodically. Once the original message store is available, you will see that the scheduled failover message forwarding processor sends the messages to the original store and then that the scheduled message forwarding processor forwards the messages to the back-end service.