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Nodejs Cluster with MQTT client [message #1843925]

Tue, 24 August 2021 15:19

Ambar Adhikari

Messages: 1
Registered: August 2021

Junior Member

I have a nodejs engine that uses MQTT to subscribe to messages from many IoT devices. As the number of IoT devices has increased, I want to run the nodejs engine in a cluster mode. This results in every cluster receiving all the MQTT messages. Is there a way to avoid this? A way in which one MQTT message will be received only once and the load of servicing the messages can be equally distributed.
Setup:
Nodejs Engine with MQTT client running via pm2 in an EC2 instance.
MQTT broker running in another EC2 instance.

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Re: Nodejs Cluster with MQTT client [message #1843941 is a reply to message #1843925]

Wed, 25 August 2021 08:31

Roger Light

Messages: 90
Registered: September 2013

Member

Yes, you can use MQTT v5 shared subscriptions. The client doesn't even need to support MQTT v5.

If you want to subscribe to my/topic, then instead subscribe to $share/<sharename>/my/topic

The <sharename> effectively defines a group. Within that group, only a single client will receive a given publish message.

So for example, if you had the following subscriptions:

Client A: $share/group1/my/topic
Client B: $share/group1/my/topic
Client C: $share/group1/my/topic

Client D: $share/group2/my/topic
Client E: $share/group2/my/topic

And then published four messages to my/topic, then the clients would receive the following messages:

Client A: message1, message4
Client B: message2
Client C: message3

Client D: message1, message3
Client E: message2, message4

I hope that helps.

Regards,

Roger

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