Cleaning up dormant actors in Azure Service Fabric

Question

I'm evaluating Service Fabric for an IoT-style application using the model that each device has its own actor, along with other actors in the system. I understand that inactive actors will be garbage-collected automatically but their state will persist for when they are reactivated. I also see there is a way to explicitly delete an actor and its state.

In my scenario I'm wondering if there are any patterns or recommendations on how to handle devices that go dormant, fail or "disappear" and never send another message. Without an explicit delete their state will persist forever and I would like to clean it up automatically, e.g.: after six months.

Answer 1

Here's a method that works.

private async Task Kill()
{
     // Do other required cleanup
     var actorToDelete = ActorServiceProxy.Create(ServiceUri, Id);
     await actorToDelete.DeleteActorAsync(Id, CancellationToken.None).ConfigureAwait(false);
}

Then just call this method using the following line:

var killTask = Task.Run(Kill);

This will spin up a new thread that references the actor, which will be blocked until the current turn has ended. When the task finally receives access to the actor, it will delete it. The beauty is that this can be called within the actor itself, meaning they can "self-delete".

Answer 2

You'll have to do this kind of clean-up yourself by writing a "clean-up" service that periodically checks for dormant actors and deletes them. The actor framework doesn't keep track of last deactivated time, so your individual actors will have to do that (which is easy enough, you have an OnDeactivate event that you can override in your actor class and save a timestamp there).

This clean-up service can be your actor service itself even, where you can implement RunAsync and do periodic clean-up work there.

Answer 3

Actors have a method OnPostActorMethodAsync which is called after every actor method is invoked (unless the method throws an exception, but I believe that's a bug). You could schedule a "kill me" reminder in that method to fire after X period of time. Every time an actor method is called that time will get pushed back. When the "kill me" reminder finally does fire, simply delete all the actor's state, and unregister any reminders. Eventually SF will kick it out of memory, and at that point, I believe the actor has essentially been deleted(not in memory, no persisted state.)