How Does Azure Interrupt a Worker Role For Deployment?

Question

I'm moving some background processing from an Azure web role to a worker role. My worker needs to do a task every minute or so, possibly spawning off tasks:

while(true){
    //start some tasks

    Thread.Sleep(60000);
}

Once I deploy, it will start running forever. So later, when I redeploy, how does Azure stop my process for redeployment?

Does it just kill it instantly? Is there a way to get a warning that it's shutting down? Do I just have to make sure everything is transactional?

Answer 1

When a role (either worker or web) is asked to gracefully shut down (because it is being scaled down or because you've asked for a redeployment) the OnStop method of the RoleEntryPoint class is called. This is the same class which has the Run method which likely either contains your loop or calls the code that contains that loop.

A couple of things to note here: The OnStop has 5 minutes to actually stop, after that the process is simply killed. If you have to call something else to shut down asynchronously, you'll need the thread in OnStop to be kept busy waiting until that other process is shut down. Once execution has left OnStop the platform assumes the machine can be shut down.

If you need to gracefully stop processing but it not require a shutdown of the machine then you can put a setting in the service config file that you can update to indicate work should be done or note. So for example a bool that says "ProcessQueues". Then in your onStart in RoleEntryPoint you hook the RoleEnvironmentChanging event. Your event handler then looks for a RoleEnvironmentConfigurationSettingChange to occur and then checks the ProcessQueues bool. If it is true it either starts up or continues processing, if it is false it stop the processing gracefully. You can then do a config change to control when things are running or not. This is one option of handling this and there are many more depending on how quickly you need to stop processing, etc.