Our front-end MVC3 web application is using AsyncController, because each of our instances is servicing many hundreds of long-running, IO bound processes.
Since Azure will terminate “inactive” http sessions after some pre-determined interval (which seems to vary depending up on what website you read), how can we keep the connections alive?
Our clients MUST stay connected, and our processes will run from 30 seconds to 5 minutes or more. How can we keep the client connected/alive? I initially thought of having a timeout on the Async method, and just hitting the Response object with a few bytes of output, sort of like chunking the response, and then going back and waiting some more. However, I don’t think this will work, since MVC3 is handling the hookup of an IIS thread back to the asynchronous response, which will have already rendered a view at that time.
How can we run a really long process on an AsyncController, but have the client not be disconnected by the Azure Load Balancer? Sending an immediate response to the caller, and asking that caller to poll or check another resource URL is not acceptable.
Azure load balancer idle time-out is 4 minutes. Can you try to configure TCP keep-alive on the client side for less than 4 minutes, that should keep the connection alive?
On the other hand, it’s pretty expensive to keep a connection open per client for a long time. This will limit the number of clients you can handle per server. Also, I think IIS may still decide to close a connection regardless of keep-alives if it thinks it need the connection to serve other requests.