Thursday, May 09, 2013

Virtual Machines Are The New Processes

Once upon a time, threads were a new thing. Hardcore Unix architectures were processes-only, cheap forking, and would have none of this lightweight threads business. Some system architects -- stuck in the 1970s -- still produce architectures for modern operating systems that consist of dozens of processes. I have personally seen a complex UI application on Windows that relies on >35 processes, of which eight different processes display parts of the application's UI (at the same time!). There is much good to be said about the isolation benefits of multiple processes, but having a Unix-inspired fear of threads is often completely unjustified today, especially in face of the cost of inter-process communication and the complexity of starting up, coordinating, and shutting down multiple processes.

I am now seeing the same thing happening with virtual machines. It is very cheap to put up a virtual machine on Azure, Amazon, or Rackspace. Very easy, too, and scriptable -- in ten minutes' time you can set up a farm of twenty virtual machines doing your bidding. This leads to architectures where every system component -- which used to live in a separate process or thread -- now lives in a separate virtual machine. Starting up, coordinating, and shutting down multiple virtual machines is harder and slower than doing the same with processes, and it seems to me that we're falling into the same trap again.

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