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Question

I am working to port an application which was designed to work in a non-Azure environment. One of the elements of the architecture is a singleton which does not scale, and which I'm hoping to replace w/ multiple worker processes serving the resource that the singleton currently provides.

I have the necessary changes in place to replace the singleton, and am at the point of constructing the communications framework to provide interconnection from the UI servers to the resource workers and I'm wondering if I should just use a TCP binding on a WCF service or whether using the Azure Service Bus would make more sense. The TCP/WCF is easy, but doesn't solve the complete problem: how do I ensure that only one worker processes a UI request?

From reading the available documentation, it sounds like the service bus will solve this, but I've yet to see a concrete example of implementation. I'm hoping someone here can assist and/or point me in the right direction.

Answer 1

Seems that Azure Service Bus queues are the right solution for you.

Azure Service Bus can be used in 3 different ways:

• Queues
• Topics
• Relays

From windows azure site:

Service Bus queues provide one-way asynchronous queuing. A sender sends a message to a Service Bus queue, and a receiver picks up that message at some later time. A queue can have just a single receiver

You can find more info at: http://www.windowsazure.com/en-us/develop/net/fundamentals/hybrid-solutions/

Answer 2

Adding to Davide's answer.

Another alternative would be to use Windows Azure Queues . They are designed to facilitate asynchronous communication between web and worker roles. From your web role you push messages into a queue which is polled by your worker roles.

Your worker role can "Get" one or more messages from a queue and work on those messages. When you get a message from a queue, you can instruct the queue service to make those messages invisible to other callers for a certain amount of time (known as message visibility timeout ). That would ensure that only worker role instance get to work on a message.

Once the worker role has completed the work, it can simply delete the message. If there's an error in processing the message, the message automatically reappears in the queue once the visibility timeout period has expired. You may find this link helpful: http://www.windowsazure.com/en-us/develop/net/how-to-guides/queue-service/ .

Answer 3

Azure queues are not designed for inter process communication, but inter-application communication. The message delivery latency is substantial, and delivery timing cannot be guaranteed. Websockets or NetTcpBinding is more suitable for applications that talk to eachother in realtime. Although must admit, you get some free stuff with queuez, especially the locking mechanisms. Just my 2 cents