ESP32 Forum

Hello.

I would like to ask more experienced people who can answer the questions:
1) How does an MQTT client (IoT device) know about the existence of a MQTT broker?
2) How does an IoT device (that using MQTT) know which topic to publish / subscribe to?
3) If you sculpt MQTT + SSL, then how is the issue of expiring keys \ sertificates resolved? Except to upload them together with the firmware every time.

Thank you.

1) you made me curious; I found this: http://dagrende.blogspot.com/2017/02/fi ... p.html?m=1
2) I don't understand: when you make a phone call how do you know what to say?
3) one way: subscribe to topic for new certificates.

Tom Meyers

tommeyers wrote: ↑

Sun Oct 03, 2021 12:21 pm

2) I don't understand: when you make a phone call how do you know what to say?
Tom Meyers

I.e. should topics be set, for example, through the configuration page? Don not understand how new IoT device choose topics...

The sender sets the topic of a message. Others subscribe to a pattern of a topic.

For example my iot device sends write topics with data to be written to a db. My Java program subscribes to writes and puts the data in a db.

My mgmt program can send a who topic. My iot devices all subscribe to who topic and reply with IAM topics and a description of who the are.

My mgmt program send what + iot device name. One device will subscribe and respond with a list of sett able and read only values. ...

Using pub-sub I receive data to be written, set iot node parameters and check health from a Java console pgm. My implementation of iot sensors is pretty complete. Many iot devices, one mgmt console, One or more db writers. The mgmt console can subscribe to any topic and can listen to the stream of data being written to the db or other streams

My design is more intricate than I described in one area. messages directed at a topic can include a return topic. The lack of that being directly supported in mqtt does not mean it can't be implemented in the clients.

Tom

Thank you, Tom. This is useful to me.