I have a question: how do these systems handle webhooks ? Do they generate event handlers too ? I'm asking this because notions like "quality of service" are essential when you're dealing with the semantically asynchronous parts of an API. With MQTT you can chose between QOS 0 (at most one, this is fire and forget HTTP events, very bad), QOS1 (at least once) and QOS2 (exactly once). This imply coding some kind of broker that will track the state of the communication and carry it to its completion.