| [hono-dev] Topic structure for protocol adapters (MQTT and REST) |
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Hello to all, after having introduced credentials for the MQTT adapter and soon for the REST adapter as well, it became obvious that the current structure of topics is not intuitive and even contradictory to the basic concept of the Credentials API: not forcing devices to know their "logical device id" when communicating with the adapters. Thus I like to discuss a new concept for the topic structure based on discussions between @sophokles78 (Kai) and @sysexcontrol (me): publish data to "telemetry" instead of "telemetry/tenantId/logicalDeviceId". ** What is the problem?** Currently, we defined the topic structure "[telemetry|event]/tenantId/deviceId", both for MQTT and for REST. This is fine for the unauthenticated case, since Hono needs to know where to send data to when a device wants to publish data. But now we have the credentials API integrated into the MQTT adapter and it became obvious that this topic structure causes problems (being outlined in the following lines). For simplicity, let's focus on how this works for MQTT (REST will be discussed later). The steps for a device are: 1.) A device authenticates itself by providing some kind of secret, for example "authId@tenantId/password". The "authId" (or name it "technicalDeviceId") is usually not the same as the "logicalDeviceId" that is used inside of Hono and the solutions (see Credentials API). - the device opens a MQTT connection and provides the "authId@tenantId/password" which is checked. If not successful, the connection is closed. - in multi-tenancy configurations, the authId contains the tenantId as well (like "sensor1@myTenant") 2.) After successful authentication the device wants to publish data. But the question is : to what topic ?
- it needs to use the topic "telemetry/tenantId/logicalDeviceId". - before the publish is accepted, the logicalDeviceId is taken to check with the device registry if the device is enabled 3.) And these are the problems: - for publishing, the device needs to know the logicalDeviceId (fatal, since it contradicts to the concept to decouple the device from the logicalDeviceId) - it needs to fill in the same tenant again that was necessary during authentication already (not fatal, but annoying, it did tell Hono the tenantId already, why again?) ** What would be the better solution? ** In typical production installations, devices are authenticated first, and Hono knows all it needs for letting the device just publish it’s data. So a MQTT device would : - authenticate itself and gets an open connection - publishes it's data only to "telemetry" or "event" (no need for tenantId or even logicalDeviceId anymore) - the check with the device registry for the device being enabled still is necessary There is just no necessity anymore for it to fill in already known data: the authenticated device just publishes to "telemetry" or "event". That's it. ** What is the topic structure for installations without authentication? ** This use case was the reason for the current topic structure, so there would be no changes to that: - "[telemetry|event]/tenantId/logicalDeviceId" would still have to be used ** How do we handle the same topic for the REST adapter? ** For REST I would like to postpone the detailed proposal. It will mainly be a consequence of what we have discussed here (there would be several changes for simplification as
well). Just to not let this point to become even lengthier as it already is. **What is your feedback to that proposal?** Note that it is not only an improvement, partially it is a pure necessity, since the logicalDeviceId must not be known to the device and we need to change that. Looking forward to a discussion, feedback, ideas! Thanks, sysexcontrol (Karsten)
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