The webification of applications over the years has led to the belief that client-server as an architecture is dying. But very few beliefs about architecture have been further from the truth.

The belief that client-server was dying - or at least falling out of favor -  was primarily due to fact that early browser technology was used only as a presentation mechanism. The browser did not execute application logic, did not participate in application logic, and acted more or less like a television: smart enough to know how to display data but not smart enough to do anything about it.

But the sudden explosion of Web 2.0 style applications and REST APIs have changed all that and client-server is very much in style again, albeit with a twist. Developers no longer need to write the core of a so-called "fat client" from the ground up. The browser or a framework such as Adobe AIR or Microsoft's Silverlight provide the client-side platform on which applications are developed and deployed. These client-side platforms have become very similar in nature to their server-side cousins, application servers, taking care of the tedious tasks associated with building and making connections to servers, parsing data, and even storage of user-specific configuration data.

bloated-man Even traditional thin-client applications are now packing on the pounds, using AJAX and various JavaScript libraries to provide both connectivity and presentation components to developers in the same fashion that AIR and Silverlight provide a framework for developers to build richer, highly interactive applications. These so-called RIAs (Rich Internet Applications) are, in reality, thin-clients that are rapidly gaining weight.

One of the core reasons client-server architecture is being reinvigorated is the acceptance of standards. As developers have moved toward not only HTTP as the de facto transport protocol but HTML, DHTML, CSS, and JavaScript as primary client-side technologies so have device makers accepted these technologies as the "one true way" to deliver applications to multiple clients from a single server-side architecture.

It's no longer required that a client be developed for every possible operating system and device combination. A single server-side application can serve any and all clients capable of communicating via HTTP and rendering HTML, DHTML, CSS, and executing client-side scripts. Standards, they are good things after all.

Client-server architectures are not going away. They have simply morphed from an environment-specific model to an environment-agnostic model that is much more efficient in terms of development costs and ability to support a wider range of users, but they are still based on the same architectural principles. Client-server as a model works and will continue to work as long as the infrastructure over which such applications are delivered continue to mature and recognize that while one application may be capable of being deployed and utilized from any device that the environments over which they are delivered may impact the performance and security of those applications.

The combination of fatter applications and increasing client-side application logic execution means more opportunities for exploitation as well as the potential for degradation of performance. Because client-server applications are now agnostic and capable of being delivered and used on a variety of devices and clients that they are not specifically optimized for any given environment and developers do not necessarily have access to the network and transport layer components they would need in order to optimize them. These applications are written specifically to not care, and yet the device and the location of the user and the network over which the application is delivered is relevant to application performance and security.

The need for context-aware application delivery is more important now than ever, as the same application may be served to the same user but rendered in a variety of different client environments and in a variety of locations. All these variables must be accounted for in order to deliver these

fat clientsRIAs in the most secure, performant fashion regardless of where the user may be, over what network the application is being delivered, and what device the user may be using at the time.

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