JMS Colocated Failover Recover Only Example

This example demonstrates how you can colocate live and backup servers in the same VM. We do this by creating an HA Policy that is colocated. colocated means that backup servers can be created and maintained by live servers on behalf of other requesting live servers. In this example we create a colocated shared store server that will scale down. That is it will not become live but scale down the journal to the colocated live server.

This example starts 2 live servers each will request the other to create a backup.

The first live server will be killed and the backup in the second will recover the journal and recreate its state in the live server it shares its VM with.

The following shows how to configure the backup, the slave is configured <scale-down/> which means that the backup server will not fully start on fail over, instead it will just recover the journal and write it to its parent live server.

     <ha-policy>
         <shared-store>
             <colocated>
                 <backup-port-offset>100</backup-port-offset>
                 <backup-request-retries>-1</backup-request-retries>
                 <backup-request-retry-interval>2000</backup-request-retry-interval>
                 <max-backups>1</max-backups>
                 <request-backup>true</request-backup>
                 <master/>
                 <slave>
                     <scale-down/>
                 </slave>
             </colocated>
         </shared-store>
     </ha-policy>
     
     

Notice that we dont need to specify a scale down connector as it will use most appropriate from the list of available connectors which in this case is the first INVM connector

One other thing to notice is that the cluster connection has its reconnect attempts set to 5, this is so it will disconnect instead of trying to reconnect to a backup that doesn't exist.

Example step-by-step

To run the example, simply type mvn verify -Pexample from this directory

1. Get an initial context for looking up JNDI for both servers

           
    initialContext1 = getContext(1);
    initialContext = getContext(0);
   
        

2. Look up the JMS resources from JNDI

           
    Queue queue = (Queue)initialContext.lookup("/queue/exampleQueue");
    ConnectionFactory connectionFactory = (ConnectionFactory)initialContext.lookup("/ConnectionFactory");
    ConnectionFactory connectionFactory1 = (ConnectionFactory)initialContext1.lookup("/ConnectionFactory");
           
        

3. Create a JMS Connections

           
    connection = connectionFactory.createConnection();
    connection1 = connectionFactory1.createConnection();
           
        

4. Create a *non-transacted* JMS Session with client acknowledgement

           
    Session session = connection.createSession(false, Session.CLIENT_ACKNOWLEDGE);
    Session session1 = connection1.createSession(false, Session.CLIENT_ACKNOWLEDGE);
           
        

5. Create a JMS MessageProducer

           
    MessageProducer producer = session.createProducer(queue);
    MessageProducer producer1 = session1.createProducer(queue);
           
        

6. Send some messages to both servers

          
    for (int i = 0; i < numMessages; i++)
    {
      TextMessage message = session.createTextMessage("This is text message " + i);
      producer.send(message);
      System.out.println("Sent message: " + message.getText());
      message = session1.createTextMessage("This is another text message " + i);
      producer1.send(message);
      System.out.println("Sent message: " + message.getText());
    }
          
        

7. Crash server #0, the live server

          
    killServer(0);
          
        

8. start the connection ready to receive messages

           
    connection1.start();
           
        

9. create a consumer

           
    MessageConsumer consumer = session1.createConsumer(queue);
            
        

10. Receive and acknowledge all of the sent messages, notice that they will be out of order, this is because they were initially round robined to both nodes then when the server failed were reloaded into the live server.

           
    TextMessage message0 = null;
    for (int i = 0; i < numMessages * 2; i++)
    {
       message0 = (TextMessage)consumer.receive(5000);
       System.out.println("Got message: " + message0.getText());
    }
    message0.acknowledge();
           
        

11. And finally (no pun intended), always remember to close your JMS resources after use, in a finally block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects

           
    finally
    {
       if (connection != null)
       {
       connection.close();
       }

       if (initialContext != null)
       {
       initialContext.close();
       }
       if (connection1 != null)
       {
       connection1.close();
       }

       if (initialContext1 != null)
       {
       initialContext1.close();
       }
    }