Load-balancing an Enterprise Service Bus

There's a great article by Lori MacVittie over at F5's DevCentral describing the case for load-balancing your Enterprise Service Bus: Load Balancing as an ESB Service. As load balancers get more and more sophisticated and SOA gets more and more widely deployed, architects are beginning to realise how all the great things a traffic manager can do for a website can be used deep within an SOA application as well.

SOA applications, particularly public-facing ones, face the same problems of reliability, performance, scalability and management that websites and other services do. An Enterprise Service Bus (ESB) will give you some headway in scaling and monitoring SOA services, but its performance is generally limited compared to a specialized load balancer. ESBs only perform shallow monitoring and they can be catastrophic single points of failure in their own right.

Service Delivery Controller

Gartner first used the term 'Application Delivery Controller' (ADC) to describe load-balancing devices that actively manage traffic to networked applications, generally web-based.

In homage to this, we use the term 'Service Delivery Controller' to describe the same technology used within an SOA application. You can regard an SDC as simply an ADC with the additional intelligence to inspect, understand and manipulate the XML payloads used in SOA traffic (SOAP).

• Factsheet: What is a Service Delivery Controller?

The Enterprise Service Bus

The SDC is fundamentally a load-balancer for an Enterprise Service Bus (ESB).

Not only does it allow you to scale your ESB and remove single points of failure; the SDC can offload a large number of tasks that the ESB performs:

• SSL acceleration
• HTTP protocol optimization
• XML-based content routing
• XML transformation and protocol translation
• SOA governance, ensuring fair access to resources
• XML-based security, checking SOA traffic meets particular criteria (DTDs, Schemas) and protecting against known weaknesses
• Response Verification

This offloading reduces the load on the ESB device and will deliver significant performance improvements to SOA applications.

Service Oriented Networking

When you begin to add such SOA-aware services, you begin to build what is sometimes referred to as a 'Service Oriented Network'.

A 'Service Oriented Network' acknowledges that the transmission of SOA traffic is the role of the network, but that new services are needed to support the needs of SOA applications. In essence, SON recognizes that the network needs to become as agile, flexible and nimble as the SOA applications it is supporting.

The KnowledgeHub article "Managing XML SOAP data with TrafficScript" describes some of the ways you can build these services using ZXTM and TrafficScript™.

For a more detailed assessment, take a look at the Building a Service Oriented Network using a Service Delivery Controller white paper on www.zeus.com.

Where's it all going?

Zeus is not the only ADC vendor who is looking at this 'service delivery controller' concept, although I'd contend that ZXTM's TrafficScript™ and XML processing are the most powerful and mature examples of SDC capabilities in the industry. Radware, Vordel, Cisco, even Nortel have products in this space; Citrix are acquiring XML technology and F5 won't be far behind either.

Lori MacVittie's Application Delivery Network blog is a great place for some more background reading.

It's going to be interesting to observe how the incumbent ESB vendors react to these developments, but with some research indicating a success rate as low as 37% it's clear that there are a number of cases where an SDC is the best and most immediately available solution.

Owen Garrett [Zeus Dev Team] 15 November 2007