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RabbitMQ Use Cases

The following are some of the main RabbitMQ use cases of WSO2 Micro Integrator.

Before executing the use cases need to connect WSO2 Micro Integrator with RabbitMQ.

Micro Integrator as a RabbitMQ Message Consumer

This section describes how the Micro Integrator can be configured as a RabbitMQ message consumer.

The following is a sample scenario that demonstrates how WSO2 Micro Integrator is configured to listen to a rabbitMQ queue, consume messages, and send the messages to an HTTP back­-end service.

Synapse configuration

<proxy xmlns="http://ws.apache.org/ns/synapse" name="AMQPProxy" transports="rabbitmq" statistics="disable" trace="enable" startOnLoad="true">
<target>
 <inSequence>
   <log level="full"/>
   <property name="OUT_ONLY" value="true"/>
   <property name="FORCE_SC_ACCEPTED" value="true" scope="axis2"/>
    <send>
     <endpoint>
       <address uri="http://localhost:9000/services/SimpleStockQuoteService"/>
     </endpoint>
    </send>
 </inSequence>
</target>
 <outSequence>
   <drop/>
 </outSequence>
    <parameter name="rabbitmq.queue.name">queue</parameter>
    <parameter name="rabbitmq.exchange.name">exchange</parameter>
    <parameter name="rabbitmq.connection.factory">AMQPConnectionFactory</parameter>
   <description/>
</proxy>

Micro Integrator as a RabbitMQ Message Producer

This section describes how WSO2 Micro Integrator can be used to send messages to a RabbitMQ queue.

Following is a sample scenario that demonstrates how the Micro Integrator is configured to listen to HTTP requests and publish them to a RabbitMQ server (message exchange).

Synapse configuration

<proxy xmlns="http://ws.apache.org/ns/synapse" name="AMQPProducerSample" transports="http" statistics="disable" trace="disable" startOnLoad="true">
<target>
 <inSequence>
    <property name="OUT_ONLY" value="true"/>
    <property name="FORCE_SC_ACCEPTED" value="true" scope="axis2"/>
     <send>
      <endpoint>
       <address uri="rabbitmq:/AMQPProducerSample?rabbitmq.server.host.name=localhost&amp;rabbitmq.server.port=5672&amp;rabbitmq.queue.name=queue&amp;rabbitmq.queue.route.key=route&amp;rabbitmq.exchange.name=exchange"/>
      </endpoint>
    </send>
 </inSequence>
 <outSequence>
        <send/>
 </outSequence>
</target>
<description/>
</proxy> 

Remote Procedure Call(RPC) with RabbitMQ

You can send request-response messages using the RabbitMQ transport by implementing a Remote Procedure Call(RPC) scenario with RabbitMQ.

The following diagram illustrates a remote procedure call scenario with RabbitMQ:

The remote procedure call works as follows:

  • When WSO2 Micro Integrator starts up, it creates an anonymous, exclusive callback queue.
  • For a remote procedure call request, the Micro Integrator sends a message with the following properties:
    • reply_to : This is set to the callback queue
    • correlation_id : This is set to a unique value for every request.
  • The request is then sent to the rpc_queue.
  • The RPC Server waits for requests on that queue. When a request appears, it does the job and sends a message with the result back to the Micro Integrator server, using the queue from the reply_to field with the same correlation_id .

  • WSO2 Micro Integrator waits for data on the reply_to queue. When a message appears, it checks the correlation_id property. If it matches the value from the request, it returns the response to the application.

The following is a sample proxy service named RabbitMQRPCProxy that sends request-response messages using the RabbitMQ transport.

Synapse configuration

<proxy xmlns="http://ws.apache.org/ns/synapse"
    name="RabbitMQRPCProxy"
    startOnLoad="true"
    trace="enable"
       transports="http">
   <description/>
   <target>
    <inSequence>
        <log level="full">
            <property name="received" value="true"/>
        </log>
        <send>
            <endpoint>
            <address uri="rabbitmq://?rabbitmq.server.host.name=localhost&amp;rabbitmq.server.port=5672&amp;rabbitmq.server.user.name=guest&amp;rabbitmq.server.password=guest&amp;rabbitmq.queue.name=rpc_queue&amp;rabbitmq.queue.routing.key=rpc_queue&amp;rabbitmq.replyto.name=dummy"/>
            </endpoint>
        </send>
    </inSequence>
    <outSequence>
        <log level="full">
            <property name="response" value="true"/>
        </log>
        <send/>
    </outSequence>
   </target>
</proxy>
The following is the code for a sample RPC server:

package rpc;

import com.rabbitmq.client.AMQP.BasicProperties;
import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.rabbitmq.client.QueueingConsumer;
import java.util.concurrent.TimeoutException;
import java.io.IOException;

public class RPCServer {

    public static void main(String[] argv) {
        Connection connection = null;
        Channel channel;
        try {
            ConnectionFactory factory = new ConnectionFactory();
            factory.setHost("localhost");
            connection = factory.newConnection();
            channel = connection.createChannel();
            QueueingConsumer consumer = new QueueingConsumer(channel);
            channel.basicConsume("rpc_queue", false, consumer);

            System.out.println(" [x] Awaiting RPC requests");

            while (true) {
                String response = null;
                QueueingConsumer.Delivery delivery = consumer.nextDelivery();
                BasicProperties props = delivery.getProperties();
                BasicProperties replyProps =
                        new BasicProperties.Builder().correlationId(props.getCorrelationId()).contentType("text/xml")
                                                     .build();

                response =
                        "<soapenv:Envelope xmlns:soapenv=\"http://schemas.xmlsoap.org/soap/envelope/\" " +
                        "xmlns:ser=\"http://services.samples\" xmlns:xsd=\"http://services.samples/xsd\">\n" +
                        "   <soapenv:Header/>\n" +
                        "   <soapenv:Body>\n" +
                        "      <ser:placeOrder>\n" +
                        "         <!--Optional:-->\n" +
                        "         <ser:order>\n" +
                        "            <!--Optional:-->\n" +
                        "            <xsd:price>10</xsd:price>\n" +
                        "            <!--Optional:-->\n" +
                        "            <xsd:quantity>5</xsd:quantity>\n" +
                        "            <!--Optional:-->\n" +
                        "            <xsd:symbol>RMQ</xsd:symbol>\n" +
                        "         </ser:order>\n" +
                        "      </ser:placeOrder>\n" +
                        "   </soapenv:Body>\n" +
                        "</soapenv:Envelope>";

                String replyToQueue = props.getReplyTo();
                System.out.println("Publishing to : " + replyToQueue);
                channel.basicPublish("", replyToQueue, replyProps, response.getBytes("UTF-8"));
                channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
            }

        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (TimeoutException e) {
            e.printStackTrace();
        } finally {
            if (connection != null) {
                try {
                    connection.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

Creating the RabbitMQ proxy service

Following is a sample RabbitMQ proxy service named AMQPProxy, which consumes AMQP messages from one RabbitMQ broker and publishes them to another:

Synapse configuration

<proxy xmlns="http://ws.apache.org/ns/synapse" name="AMQPProxy" transports="rabbitmq" statistics="disable" trace="disable" startOnLoad="true">
   <target>
      <inSequence>
         <log level="full"/>
         <property name="OUT_ONLY" value="true"/>
         <property name="FORCE_SC_ACCEPTED" value="true" scope="axis2"/>
      </inSequence>
      <endpoint>
         <address
         uri="rabbitmq:/AMQPProxy?rabbitmq.server.host.name=192.168.0.3&amp;rabbitmq.server.port=5672&amp;rabbitmq.server.user.name=user&amp;rabbitmq.server.password=abc123&amp;rabbitmq.queue.name=queue2&amp;rabbitmq.exchange.name=exchange2"/>
      </endpoint>
   </target>
   <parameter name="rabbitmq.queue.name">queue1</parameter>
   <parameter name="rabbitmq.exchange.name">exchange1</parameter>
   <parameter name="rabbitmq.connection.factory">AMQPConnectionFactory</parameter>
   <description></description>
</proxy>

Note the following:

  • The transport key name is rabbitmq . You need to specify this key name in the transports parameter (ie., transports="rabbitmq" ).
  • The proxy is defined as OUT_ONLY, because it does not expect a response from the endpoint.
  • The endpoint specifies where the messages will be published. The URI prefix is rabbbitmq so that the RabbitMQ AMQP transport will be used to publish the message. Be sure to specify the rest of the parameters in the URI as shown in the sample proxy service above. If you do not know which RabbitMQ exchange to use, leave the value blank to use the default exchange.
  • The rabbitmq.queue.name parameter specifies the queue on which the proxy service listens and consumes messages. If you do not specify a name for this parameter, the name of the proxy service will be used as the queue name.
  • The rabbitmq.exchange.name parameter specifies the RabbitMQ exchange to which the queue is bound. If you do not want to use a specific exchange, leave this value blank to use the default exchange.
  • The rabbitmq.connection.factory parameter specifies the listener that listens on the queue and consumes messages. In this example, the connection factory is set to the name of the listener we created earlier (ie., AMQPConnectionFactory ).

You can modify the sample proxy service above to handle scenarios where you only want to receive AMQP messages but need to send messages in a different format, or you want to receive messages in a different format and send only AMQP messages. You can also modify the proxy service to work with a different transport. For example, you can create a proxy that uses the RabbitMQ AMQP transport to listen to messages and then sends them over HTTP or JMS.

Rolling failed messages back

In this exmaple, messages are read from an inbound (RabbitMQ) message queue via an Inbound Endpoint. If a failure occurs, the transaction will roll back. This avoids the loss of the message.

Tip

If you are using a RabbitMQ Inbound Endpoint for receiving messages, set the scope of the SET_ROLLBACK_ONLY property to default as follows:

&lt;property name="SET_ROLLBACK_ONLY" scope="default" type="STRING" value="true"/&gt;

As shown in the below example, you need to set the SET_ROLLBACK_ONLY property to true in the fault handler (e.g., the fault sequence), to roll the message back when a failure occurs.

Synapse configuration

Given below are the synapse artifact configuration for this use case. Note that the fault sequence contains the SET_ROLLBACK_ONLY property set to true.

<?xml version="1.0" encoding="UTF-8"?><inboundEndpoint xmlns="http://ws.apache.org/ns/synapse" name="rabbit-mq-dec41-inbound-endpoint" sequence="rabbit-mq-dec41-inbound-sequence" onError="rabbitmq_fault" protocol="rabbitmq" suspend="false">
    <parameters>
        <parameter name="sequential">true</parameter>
        <parameter name="coordination">true</parameter>
        <parameter name="rabbitmq.connection.factory">AMQPConnectionFactory</parameter>
        <parameter name="rabbitmq.server.host.name">localhost</parameter>
        <parameter name="rabbitmq.server.port">5672</parameter>
        <parameter name="rabbitmq.server.user.name">rabbit</parameter>
        <parameter name="rabbitmq.server.password">rabbit</parameter>
        <parameter name="rabbitmq.queue.name">RABBITMQ-INBOUND-QUEUE</parameter>
        <parameter name="rabbitmq.exchange.name">RABBITMQ-INBOUND-EXCHANGE</parameter>
        <parameter name="rabbitmq.queue.durable">true</parameter>
        <parameter name="rabbitmq.queue.exclusive">false</parameter>
        <parameter name="rabbitmq.queue.auto.delete">false</parameter>
        <parameter name="rabbitmq.queue.auto.ack">false</parameter>
        <parameter name="rabbitmq.exchange.durable">true</parameter>
        <parameter name="rabbitmq.exchange.auto.delete">false</parameter>
        <parameter name="rabbitmq.connection.ssl.enabled">false</parameter>
    </parameters>
</inboundEndpoint>
<?xml version="1.0" encoding="UTF-8"?><sequence xmlns="http://ws.apache.org/ns/synapse" name="rabbitmq_fault">
    <log level="full">
        <property name="MESSAGE" value="Executing default 'fault' sequence"/>
        <property xmlns:ns="http://org.apache.synapse/xsd" name="ERROR_CODE" expression="get-property('ERROR_CODE')"/>
        <property xmlns:ns="http://org.apache.synapse/xsd" name="ERROR_MESSAGE" expression="get-property('ERROR_MESSAGE')"/>
    </log>
        <property name="SET_ROLLBACK_ONLY" value="true" scope="default" type="STRING"/>
    <drop/>
</sequence>
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