5

You question isn't very clear. AWS IoT uses MQTT. If you squint, it's a centralized service. But it's actually a federation of many servers that create a pub-sub architecture. The AWS service adds a database on top of MQTT, so you can have shadow profiles for knowing what changed during disconnected operation. But your question could be about "finding ...


4

Subscribing to $SYS/# topic will provide some information about the broker and maybe about the clients. Detailed description of these items can be found here. There are three main categories to highlight: Static Topics: Messages on a static $SYS topic are not required to be sent on every $SYS topic update interval. These messages are sent once the ...


4

onMessageArrived will be called separately for each message that arrives so if the payload only contains one value then you will only be able to get one value at a time. You need to include a if statement in the onMessageArrived callback to determine which topic the message arrived on and then set the respective value.


3

If your node devices already speak IP protocols, have a reasonable amount of volatile and non-volatile storage, and have an outgoing network connection they should be able to connect directly with an MQTT broker. But if they use some other radio standard like zigbee then you'd need a gateway. Note that a "gateway" often need be little more than a process ...


1

Without seeing your code so we know what topics you are subscribed to this is really hard to answer. But, yes this is a totally public broker with a single shared topic space for all users. So it is very likely that you are receiving a message published by a previous user. It should really only be used to test MQTT client implementations and not for ...


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