Are application layers always a good idea?

Distributed Component Object Model reliant apps can cause problems

Applications that depend on the Distributed Component Object Model (DCOM) -- a Microsoft component that provides communications between software components across a network -- might not work properly with application layers. It is fairly common for application layering products to display warning messages if IT attempts to layer such applications.

It's not a hard-and-fast rule that DCOM apps won't work. In fact, many IT pros have been able to layer such applications without any issues, but the layering process can fail before completion with DCOM apps. In addition, the app may simply stop working after IT layers it.  

The best move for IT pros with applications that rely on DCOM components is to evaluate them on a case by case basis.

Other times to avoid application layers

It's also a good idea to avoid using application layering in conjunction with other application virtualization technologies.

Other poor candidates for application layering are applications that include boot-time services. Remember, application layers are not native to the operating system so application layering software is necessary to provide the redirection it takes for them to run. This is a problem for applications that include boot-time services, because those services must run at boot time -- before the application layering software has a chance to load. This same basic concept also applies to any software that interacts with the operating system at a low level. Examples include device drivers and third-party hypervisors.

IT pros also can't layer the layering software itself, because it must run in sequence for a layered application to execute.

It's also a good idea to avoid application layers in conjunction with other application virtualization technologies. For example, IT pros probably wouldn't want to layer a streamed application because there is a good chance that doing so would break the application.

IT pros may not be able to layer every application, but it won't hurt to try as long as they thoroughly test the layered apps before putting them into production.