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This week, we’ll explore yet another system management pattern known as Smart Proxy.

When do I use this pattern?

Smart Proxy is used when we want to monitor the Request-Reply scenario. Especially, when the Return Address pattern is applied. The Smart Proxy receives the Request and changes the Return Address to itself so that it can monitor the response. When the response arrives, Smart Proxy sends the response back to the original Return Address once the monitoring steps are complete.

Smart Proxy in CPI

Unfortunately, I could not implement the pattern in CPI. This is what I tried.

Implementation Summary

The implementation for Smart Proxy uses the example from Return Address blog. However, instead of using the Microsoft Azure Service Bus, this blog will use SAP Enterprise Messaging.

The scenario in the Return Address blog is as follows. Customer Data is sent from a sender system. However, the sender system wants a response in a separate queue. So, the sender system sets the JMSReplyTo header. The processor of customer data puts the response in the queue specified by the JMSReplyTo header. Finally, the sender can process the response.

In the Smart Proxy, we’ll intercept the first step, i.e., the request message is sent to Smart Proxy instead of directly to the queue. Smart Proxy will store the JMSReplyTo header in the Data Store with JMSCorrelationId as the Entry Id and overwrite the JMSReplyTo with its own address. In response, Smart Proxy will fetch the original message using JMSCorrelationId and put the message in the original queue specified by JMSReplyTo header.

1. Enqueueing the Customer

Enqueueing the Customer

This flow starts immediately using the Timer Start Event. Prepare Input Message Content Modifier sets the body. Set JMS Headers Content Modifier sets the JMSCorrelationId, JMSDestination, and JMSReplyTo headers. ProcessDirect Receiver Adapter will invoke the Smart Proxy flow.

Configuration of Set JMS Headers Content Modifier

The Headers tab has these entries.

2. Smart Proxy – Processing the Request Messages

Processing the Request Messages

This flow simply accepts the request message using the ProcessDirect Sender Adapter. Puts it in the Data Store with Entry Id as JMSCorrelationId using Data Store Write Operation. Next, the Set JMS Headers Content Modifier will overwrite the JMSReplyTo header with ‘queue:SmartProxy’. The AMQP Receiver Adapter will enqueue the message in the queue specified by JMSDestination header.

The headers JMSCorrelationId, JMSDestination, and JMSReplyTo are listed in the Allowed Header(s) under the Runtime Configuration tab.

Configuration of Data Store Write Operation

Configuration of Set JMS Headers Content Modifier

Configuration of the AMQP Receiver Adapter

3. Processing the Customer

Processing the Customer

This flow receives the Customer data using AMQP Sender Adapter. For simplicity, we always set the body to Successful payload using Content Modifier. Finally, the AMQP Receiver Adapter will enqueue the response in the queue specified by JMSReplyTo header.

The headers JMSCorrelationId and JMSReplyTo are listed in the Allowed Header(s) under the Runtime Configuration tab.

Configuration of the AMQP Sender Adapter

The connection tab is exactly the same as that specified in section “2. Smart Proxy – Processing the Request Messages”. The Processing tab is configured as follows:

Configuration of the AMQP Receiver Adapter

The configuration is exactly the same as that specified in section “2. Smart Proxy – Processing the Request Messages” except the Destination Name. Destination Name is set to ${header.JMSDestination}.

4. Smart Proxy – Processing the Response Messages

Processing the Response Messages

This flow consumes the messages from the SmartProxy queue using AMQP Sender Adapter. The message body is backed up to exchange property using a Content Modifier. Data Store Get Operation is used to restore the value of the original JMSReplyTo header. Next, the body is restored using another Content Modifier. Finally, AMQP Receiver Adapter enqueues the response message into queue specified by the JMSReplyTo header.

The headers JMSCorrelationId and JMSReplyTo are listed in the Allowed Header(s) under the Runtime Configuration tab.

Configuration of the AMQP Sender Adapter

The configuration is exactly the same as that specified in section 3. Processing the Customer except for the Queue Name. Queue Name is set to queue:SmartProxy.

Configuration of the Data Store Get Operation

Configuration of the AMQP Receiver Adapter

The configuration is exactly the same as that specified in section “2. Smart Proxy – Processing the Request Messages” except the Destination Name. Destination Name is set to ${header.JMSReplyTo}.

5. Processing the Customer Response

Processing the Customer Response

This flow simply consumes the responses using AMQP Sender Adapter and Logs the payload using the famous Log Groovy Script.

Configuration of the AMQP Sender Adapter

The configuration is exactly the same as that specified in section 3. Processing the Customer except for the Queue Name. Queue Name is set to queue:CustomerResponses.

The Issue and Alternatives

The issue happens in step 3. The SAP Enterprise Messaging does not return the JMSCorrelationId header. As a result, step 4 does not receive the JMSCorrelationId and fails to restore the JMSReplyTo header.

Alternative 1: Use Standard JMS

The Standard JMS does not support dynamic Queue Name in JMS Receiver Adapter. As a result, step 2 could not be implemented. In turn, Smart Proxy cannot be implemented with Standard JMS.

Alternative 2: Test other providers supported by AMQP Adapter

Perhaps, Smart Proxy could be implemented with other providers supported by AMQP Adapter like Microsoft Azure Service Bus, Solace PubSub+, Apache Qpid Broker-J, Apache ActiveMQ 5 and ActiveMQ Artemis, IBM MQ, RabbitMQ.

Please comment below if you know how to resolve the issue or if you know if any of the alternatives work :).

EIPinCPI Rating

Unfortunately, I could not implement the Smart Proxy pattern. So, I would have to rate 0 out of 10 for this pattern.

Conclusion

Smart Proxy is used to monitor messages when Return Address pattern is used.

References/Further Readings

• Smart Proxy Pattern in Enterprise Integration Patterns
• EIPinCPI
  • Request-Reply
  • Return Address
• CPI Components
  • Timer Start Event
  • Content Modifier
  • ProcessDirect Receiver Adapter
  • ProcessDirect Sender Adapter
  • Data Store Write Operation
  • AMQP Receiver Adapter
  • AMQP Sender Adapter
  • Data Store Get Operation
  • Groovy Script

Hope this helps,
Bala

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