Node-RED : MQTT subscribe on generic topic

[Claude Favreau]

Hi,

I post a message because I didn’t really find a solution about my problem. I am developing a generic flow on Node-RED that I could deploy on severals gateways. What I am trying to do is to receive some messages on a MQTT topic that I subscribed. But I didn’t find a good way to have a generic “topic” like this :

gateway/{serialNumber}/input

Where the serial number is automatically filled. Someone has had to do this stuff ? Today my solution is to create a custom MQTT node but I would like to know if there are not better solution.

Regards

[Peter Ferland]

For MQTT topics the wildcard is ‘+’ so if you wanted to subscribe to every gateway’s input topic you would use “gateway/+/input”.

If you wish to put your own string there for a specific gateway’s serial number, you’d need to build the string in a javascript node and then set the string as the topic property in the msg.

[Claude Favreau]

Hi,

Yes I am agree with you but I wouldn’t to have many charge on gateways. Therefore, to avoid this problem I need to subscribe a specific topic with the serial number for each gateway. For an input mqtt node we canot give a topic like you told me.

I think the way is to have a custom node if I want to insert the serial number from each gateway dynamically. But I would like to be sure.

Regards

[Peter Ferland]

For a MQTT input node you are correct, there is no way to programmatically set the topic on an input using the built in nodes so you would have to create a custom node to handle that.

[Claude Favreau]

Hi,

Thanks very much. I have another question linked to this post. Do you know how to create a custom Node-RED app ? Because if I overwrite or I add a custom node for MQTT, I would like to have the possibility to deploy it on severals gateway easily.

Regards

[Peter Ferland]

There is extensive discussion on adding nodes to node-red on the Conduit in this thread: http://www.multitech.net/developer/forums/topic/adding-nodes-to-node-red/page/2/

Once you figure out what commands need to be run, you can execute them in the install script in a custom application package and use DeviceHQ to deploy the custom application to each of your gateways. http://www.multitech.net/developer/software/aep/creating-a-custom-application/

[Claude Favreau]

Hi,

Thanks, it helps me in what I want to do.

Regards

[Author]

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