This is a simple example of how we set up reminder grains in Orleans and f#.

Here's the code so you can follow along

Grain interface

type IYourReminderGrain =
    inherit IGrainWithStringKey
    inherit IRemindable

    abstract member WakeUp : unit -> Task

We have 2 important parts here that will be implemented in the grain.

• IRemindable: This forces us to implement the ReceiveReminder function. This is where the logic we want to execute each time the reminder gets triggered.
• WakeUp : This activates the grain so we can set up the reminder

Grain implementation

type YourReminderGrain() =
    inherit Grain()
    interface IYourReminderGrain with
        member this.WakeUp() = Task.CompletedTask
        member this.ReceiveReminder(reminderName, status) =
            Console.WriteLine(reminderName, status)
            Task.CompletedTask

    override _.OnActivateAsync(cancellationToken:CancellationToken) = 
        let _periodInSeconds = TimeSpan.FromSeconds 60
        let _dueInSeconds = TimeSpan.FromSeconds 60
        let _reminder = base.RegisterOrUpdateReminder(base.GetPrimaryKeyString(), _dueInSeconds, _periodInSeconds)
        base.OnActivateAsync(cancellationToken)

There are 2 important parts here

• Implement the IYourReminderGrain : The WakeUp is simple as we do not want to do anything here. ReceiveReminder contains our logic. What we want to execute on every trigger of the reminder. Here we are simply writing the reminder name to the console.
• Overriding OnActivateAsync : This is where we register the reminder and specify at what interval it should trigger at. _periodInSeconds specifies the time between triggers and _dueInSeconds specifies how long to wait until the first trigger

Kicking off the reminder grain

In this example I do this by adding a hosted service GrainActivatorHostedService.

This is responsible for retrieving the reminder grain from the IGrainFctory and calling the WakeUp grain function

let! _ =
    _client
        .GetGrain<IYourReminderGrain>(Guid.NewGuid().ToString())
                    .WakeUp() 

That's it. To run the app just run

> sh run-silo-local.sh
or
> sh run-silo-docker.sh

You can also run it in your IDE or VS Code devcontainers

To verify everything is working correctly:

• Dashboard: http://localhost:8081
• Dashboard if running with Docker http://localhost:3000

This is part of the road-to-orleans project. Check it out

flowchart TD
Solution1(Solution1: One basic silo, no grains.)
Solution2(Solution2: One basic silo, one grain, one console client.)
Solution3(Solution3: One basic silo, one grain, one console client, <br/>everything containerized.)
Solution3a(Solution3a: Solution3 + grain persistence.)
Solution3b(Solution3b: Solution3 + datadog APM.)
Solution4(Solution4: First in-memory clustering example. <br/>Many silos, many clients.)
Solution5(Solution5: Solution4 where