There have been lots of questions lately about AppFabric (code named Dublin). These questions have centered around why Microsoft needs another middle tier solution and will AppFabric replace BizTalk.

Lets take a look at these questions as well as two additional questions; What is AppFabric and why does Microsoft need another middle tier solution? First, AppFabric is a distributed application server. To answer the other questions, we need to go in a little more depth.

Before .NET was released, developers working with the Microsoft technologies used COM+ to host their middle tier objects. Back then, when we needed to scale out our object oriented and object based applications we created middle tier code libraries and ’hosted’ them in COM+. The COM+ host provided instance management (just-in-time activation), role-based security, automated transaction management as well as better memory and processor management, distributed transactions and a number of other services. 

When .NET was introduced, we moved away from COM components and also moved away from using COM+ as a hosting model. This left a vacuum that so far had gone unfilled.

In attempts to fill this vacuum, individual developers had to create their own hosts. These hosts typically were Windows Services. However, these services usually didn’t include multi threading, scale out capabilities, tracking, monitoring, etc. – the types of functionality that has been in BizTalk for years. As Microsoft looked at BizTalk, as well as the .NET Framework, it was determined that there are many great features in BizTalk that if a scaled down version was available it would address gaps in the framework. Thus AppFabric was born.

For .NET developers writing applications using WCF and WF, AppFabric will fill the middle tier hosting vacuum. AppFabric will provide the host and will provide scalability and support for building out your middle tier application components. It also will simplify deployment, configuration, management and scalability of composite applications. The goal of AppFabric is to provide a server infrastructure, on which business logic developed in WF can be executed and exposed via WCF endpoints, without the need to design, develop, and support the infrastructural code.

The next question I hear is will AppFabric replace BizTalk? The answer is very clearly no.

AppFabric should be used when your architecture calls for an application level code-first object based approach. This is the same approach that is used by WF and WCF programming models and is the one that can be hosted in AppFabric and the additional functionality that AppFabric provides. AppFabric will provide a number of management and scalability features through IIS and WAS to provide the server infrastructure without the need to write the plumbing as you did before. This is a different approach than that of the XML Schema first approach that is used in BizTalk.

Use BizTalk when your architecture calls for an enterprise level message based approach. Use BizTalk when you need to isolate disparate systems that need to be connected. In point-to-point integrations, changes made to the provider system can have a profound impact on the consuming application. BizTalk natively provides a hub-based integration model which eases this burden and allows organizations to provide business services that are isolated from the impact of changes made to the systems and processes on which these services are based. This is achieved through the use of separate schemas, and the associated ability to easily develop message transformation logic using BizTalk’s Mapper tool. Use BizTalk if you have business-to-business requirements and need to integrate using technologies such as EDI, SWIFT, RosettaNet, AS2 or HL7.

The reality is that businesses will utilize both of these technologies in their different application architectures. This is not an either or decision but instead a decision of where and when to use each. 

Keep in mind, however, that many of the same terms are used to describe the functionality provided with both BizTalk and AppFabric. These terms are things like Content Based Routing, Correlation, long running transactions, etc. Although the terms are the same the implementation and functionality is different. With all decisions, make sure that you take a couple of minutes to look under the hood and ensure that you understand the differences.