CODEWITHSUNDEEP
raspberry-pimqttpublish-subscribeesp8266mosquitto
Petr Marek
Petr Marek

Reputation: 735

Is possible to publish to MQTT clients during their sleep?

I am going to implement some sort of home automation system (as my bachelor thesis). I have looked on MQTT protocol and I have two question about it.

I have saw this tutorial:
https://www.youtube.com/watch?v=X04yaaydjFo&list=PLeJ_Vi9u6KisKTSNeRRfqsASNZdHSbo8E&index=13
Which has materials (codes etc) here:
https://randomnerdtutorials.com/raspberry-pi-publishing-mqtt-messages-to-esp8266/

My first question is:
Is the logic how to manage acquired data/message (due to some topic subscription) in broker or clients? From tutorial above it seems, that that logic how to deal with message is in clients. Should it always be there? Or is it possible to has it in broker? Sorry if this question is too "abstract", i am at beginning of programming, so I have no concrete example. Basically what I want is to have as "light" program in client, as is possible (because broker will have lot of memory and computing capacity, while clients will be very limited in both).

My second question is:
Is it posible to put ESP8266 (or just any client) in sleep and awake it, let's say every 5 minutes? Of course it should not be problem if that client only publish (and never subscribe) to topics. But what when I have client, which can read some sensor, which will send in that 5 minutes cycles to broker, and also can control some of its output? Is there way to do that? Or if client is not available (if there is some data to publish to it and it is currently sleeping), the message is just thrown out? My thought was if there is way to ask broker after client awake if there was any published message to them during client sleep?

Thanks for every info! :)

Upvotes: 0

Views: 557

Answers (1)

Marcel Stör
Marcel Stör

Reputation: 23555

1. Answer

The message processing logic is to be fully implemented by the client. With MQTT there is no "stream" processing as is possible with e.g. Apache Kafka. However, you can of course have intermediary (non-IoT) clients that subscribe to the original topic, prepare a modified message and publish it to a new topic - the one which the IoT device would then subscribe to.

2. Answer

You can tell the broker to retain a message. However, it will at most retain 1 message per topic.

P.S. for the future please stick to 1-question-1-post here on SO.

Upvotes: 2

Related Questions