Why do Windows Azure not load balance while Thread.Sleep()?

Question

I am playing with the the Windows Azure emulator running an MVC website with a single controller method that calls Thread.Sleep(5000) before it returns.

On the client I run a loop that sends a POST request to the controller every 1000 ms, receives a reply from the server with the RoleEnvironment.CurrentRoleInstance.Id, and prints it on the screen.

I have 4 instances of my MVC worker role running.

I understand that the connection: keep-alive HTTP header can keep the browser from making a request to a different instance, because an existing connection is open.

But still, even when loading up my site in multiple browser windows, it keeps hanging while waiting for the Thread.Sleep(), and then (most times) continues to get replies from the same instance.

Why doesn't Azure's load balancer send subsequent requests to a non-busy worker role instance? Do I need to manually mark it as busy?

Answer 1

You mentioned using the emulator, which doesn't handle load balancing the same way as Azure's real load balancers. See this post for details about the differences. I don't know what exactly is going on in your case, but... I'd suggest you trying this out in Azure to see if you get the behavior you're expecting.