Send event from server to client

[rbagan]

Hi NVFlare community,

I would like to send an event from server to all FL clients when a new RUN starts. I'm using the NVFlare docs (https://nvflare.readthedocs.io/en/main/programming_guide/event_system.html) to do this, however, the event is fired on the server side but never reaches the client side. Any idea what I am doing wrong?

Is there another alternative to events? or are they the best option for sending data between client and server?

My intention is to send data (basic python types, e.g. string or ints) to initialize an object on client side based on the type of task the server wants to execute.

Server

class Server(FLComponent):
    def __init__(self) -> None:
        super().__init__()

    def handle_event(self, event_type: str, fl_ctx: FLContext) -> None:
        if event_type == EventType.START_RUN:
            engine = fl_ctx.get_engine()
            fl_ctx.set_prop(key="yourEventDataKey", value="yourEventData", private=True, sticky=True)
            engine.fire_event(event_type="custom_event", fl_ctx=fl_ctx)

Client

class Client(Learner):
    # init, and other functions goes here
     
    def handle_event(self, event_type: str, fl_ctx: FLContext):
        if event_type == "custom_event":
            # Do something :)

Thank you.

[chesterxgchen]

There are probably multiple-ways to achieve the goal, not necessary via the sever to client event.

1. define a workflow, you can write controller to define a workflow to do the task you like to do. You can send or broadcast the task to client(s), client receive and handle the tasks. This new workflow can be added to before or after the existing workflows

2. If above doesn't fit your needs, you can leverage use send Aux message ( 2.3.x or before), which directly send the target audiences (client or server). split learning example used this approach. Aux channel API will be hidden to use after 2.4.x as 2.4.0 will provide more higher level abstraction to achieve the same goal

3. what about using event directly.
   As far as I know, you can send Fed Event from Client to Server ( This is how Tensorboard Streaming/Experiment tracking feature based on), not sure you can direct send event from Server to client besides aux channel message.
   All tasks are pull-based, i.e. server send the task to task queue, the client pull task from the queue.

hope this helps

[rbagan]

Thank you @chesterxgchen!

[yhwen]

On the server, instead of using engine.fire_event(), change to use engine.fire_fed_event(), then this will fire the event to the client side.

[chesterxgchen]

@rbagan looks like my answer is not totally correct. the NVFLARE is able to sent the event from server to client. as @yhwen is described.