Generic EventSource

Generic eventsource extends Argo-Events eventsources via a simple gRPC contract. This is specifically useful when you want to onboard a custom eventsource implementation.

Contract

In order to qualify as generic eventsource, the eventsource server needs to implement following gRPC contract.

    syntax = "proto3";

    package generic;

    service Eventing {
        rpc StartEventSource(EventSource) returns (stream Event);
    }

    message EventSource {
        // The event source name.
        string name = 1;
        // The event source configuration value.
        bytes config = 2;
    }

    /**
    * Represents an event
    */
    message Event {
        // The event source name.
        string name = 1;
        // The event payload.
        bytes payload = 2;
    }

The proto file is available here.

Architecture

Consider a generic eventsource.

    apiVersion: argoproj.io/v1alpha1
    kind: EventSource
    metadata:
      name: generic
    spec:
      generic:
        example:
          insecure: true
          url: "generic-event-source-server.argo-events.svc:8080"
          config: |-
            key1: value1
            key2: value2

The values placed under config field follows a free-form style and Argo-Events eventsource client is not opinionated about them. Although, it is expected that the eventsource server implemented by the user is able to parse the configuration.

Flow

1. The eventsource client connects to the server via the url defined under eventsource spec and sends over the configuration defined under config over an RPC call.

2. The eventsource server then parses the configuration and connects to any external source if required to consume the events. The eventsource server can produce events without connecting to any external source, e.g. a special implementation of calendar events.

3. The events from eventsource server are streamed back to the client.

4. Client then writes the events to the eventbus which are read by the sensor to trigger the workflows.

Connection Strategy

The eventsource client performs indefinite retries to connect to the eventsource server and receives events over a stream upon successful connection. This also applies when the eventsource server goes down.