title: Which architecture is more scalable
body: <p>I'm developing a application for <em>Windows <strong>azure</strong> cloud service</em>.</p>
  
  <p>The general description for the application is quite simple: a front end on MVC 4, a middle tier for processing front-end processing requests and a SQL Azure/Blob backend...</p>
  
  <p>I did not started to write code so far, and before that i would like to get some feedback on the which of the following scenario would models is more scalable and possibly why. If you think that theres a N'th option that i did not considered please expose it!</p>
  
  <p>Just to be clear single tier app is out of question.</p>
  
  <blockquote>
    <p><strong>Scenario 1:</strong><br>
    Front-End consumes a WCF service on middle tier that does all the processing.</p>
    
    <p><strong>Scenario 2:</strong><br>
    Front-End consumes a WCF service on middle tier that queues up that request on a SB and waits. "Tier 3" consumes the message and processes it, also queueing the answer for WCF Service to respond...</p>
    
    <p><strong>Scenario 3:</strong><br>
    Front-End queues a message and loops waiting for response message. "Tier 3" consumes the message, processes it and re-queue it for Front-End to stop waiting...</p>
  </blockquote>
  
  <p>Basically all the questions resume to "How well WCF scales-out horizontaly?"...</p>