Architecting Server/Client Convergence

In this post I argue that the current convergence of Desktop and / Web Apps (RIAs) suggests a convergence of Server and Clients and that this opens up some interesting possibilities.

I have been following an interesting series of posts by Arnon Rotem-Gal-Oz on the web/desktop convergence trend (all four posts are worth reading!). As well, in January and April, Arnon observes software converging towards:

  • the ease of deployment of web applications,
  • the richness and responsiveness of desktop apps,
  • using a unified programming model for the whole app.

Technologies competing for the privilege of delivering some or all of this trifecta include (but are not limited to) AJAX, Adobe Flex, Flash, Adobe Air, Microsoft Silverlight, JavaFX, Google Gears, Mozilla Prism, Aptana’s Jaxer and JNext.

These technologies are being developed in the context of increasing awareness of two trends 1) the possibilities of ‘on-tap’ cloud computing and simultaneously 2) the promise of 100’s of cores in our client computers.

Here are some observations about the current web-app situation:

  • Increasingly, the Virtual Machine environments on the server are being introduced down the tiers and ported to clients. (Silverlight’s CLR, and Java VM come to mind.)
  • The use of Javascript in browsers has taught us about the secure use of mobile code and a similar mechanism could be inductively applied back up the tiers so that servers also are extensible like browsers. (Unlike the movement of server VMs into clients, I am not aware of production or prototype implementations of this.) Aptana’s Jaxer is a great example of this. (Thanks to Peter Svensson for pointing this out.) See Request Based Distributed Computing for a candidate architecture.

What we are seeing is not just a Web/ Desktop Convergence but also the possibility of Server/Client Convergence.

This convergence has the potential to address another problem in the current state of affairs with web apps:

  • Forcing the developer to choose in advance about the location of code execution is like forcing the developer to place a long running bet on the relative performance of the cloud, network and heterogeneous clients.

Actually, this is one of the drivers underlying Microsoft Volta – a technology that is designed to reduce the cost of reassigning portions of an application between server and client. However as Arnon has pointed out it does not provide an abstraction that reinforces the “coarse-grained interface” that works well in the context of the fallacies of distributed computing. Unlike Volta, tier-agnostic requests relies on the same coarse grained interface as AJAX.

Convergence of server and client technologies
However, the convergence of server and client technologies opens up the possibility for Request Based Distributed Computing and tier-agnostic requests to provide a simple mechanism for delaying architectural decisions to run-time as well as supporting:

  • the ease of deployment of web applications,
  • the richness and responsiveness of desktop apps,
  • using a unified programming model for the whole app.

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