Events in SlimFaas

SlimFaas supports a basic “publish/subscribe” model for broadcasting events to ready replicas of subscribed functions. This can be used to trigger internal actions or notify your functions of certain events.

1. Subscribe to Events

To allow a function to receive events, add the annotation SlimFaas/SubscribeEvents to the function's deployment:

metadata:
  annotations:
    SlimFaas/SubscribeEvents: "Public:my-event1,Private:my-event2,my-event3"

• Public events can be sent from any source.
• Private events can only be sent by trusted pods or within the same namespace.
• If you omit Public: or Private:, it defaults to SlimFaas/DefaultVisibility.

2. Publishing an Event

Use the following HTTP route to publish an event:

• Endpoint: POST http://<slimfaas>/publish-event/<eventName>/<path>

• Body (any JSON payload):

{
  "data": "my-event-data"
}

• Response: 204 (No Content)

3. Delivery behavior

HTTP publication does not wake sleeping replicas or queue events durably. Wake subscribers and wait for readiness before publishing. A configured subscriber with no ready replicas can still lead to a 204 response, while no allowed subscription returns 404. Per-target failures are logged, so 204 is not an acknowledgment from every replica.

Connected WebSocket subscribers receive events through their registered clients. Use async function calls when work needs a durable queue, and the Guided Tour to observe fan-out in the UI.

4. Example

curl -X POST -H "Content-Type: application/json" \
     -d '{"input":10}' \
     http://localhost:30021/publish-event/fibo-public/fibonacci

In the supplied demo, ready replicas subscribed to fibo-public receive a POST at /fibonacci. Use port 30020 instead in native local mode.

One publication can reach multiple ready replicas of the same function. 204 describes the publication response; it does not prove that every subscriber processed the payload.