After deploy flow containing mqtt node, new connection is created, old connection remains open

General
#1

Having a simple flow with a mqtt node (broker clientId set to autogenerated, port 8883).

After first deploy there is exactly one connection to the mqtt broker.
(sudo netstat -nputw | grep 8883)

With each subsequent deployment the number of connections increases, as always a new connection is created and the old one is not disconnected...

If using a fixed clientId the issue does not occur - the number of connections is always 1.

using node-red v2.2.2

#2

What broker are you using and how have you configured the connection?

#3

I suspect it is the very same issue am working on right now.

Thanks for letting us know.

I'll keep you posted when a solution is found.

PS: In the mean time - use "Modified Nodes" method to minimise the impact (especially if you are NOT modifying an MQTT node) because "Full" causes all nodes (even ones you havent touched) to be re-created.

image

#4

tried with different broker's (hivemq, mosquitto)

#5

thanks for suggestion with 'Modified Nodes'.

#6

QOS value and retain will change the behaviour. Upon losing the connection with a client the broker will maintain the connection for a while so that the same client reconnects it will find the messages waiting for him.
When using the same client_id you force reusing the same "queue" hence the same TCP connection on the broker.

#7

I would say that "Clean session" is key
I'm using either one of those 2 combinations:

  • empty (automatic) client_id and "Clean session" checked : the broker clear the client context in case of disconnection
  • fixed client_id and "Clean session" unchecked : the broker keeps the client context in case of temporary disconnection. If a new connection comes with the same client_id, the older one is closed by the broker.

I don't say that other combinations are useless, just that I have no use-case for them.

So from your description it looks like the combination of "automatic client_id" and "Clean session unchecked" leaves MQTT connection in the background that are neither closed by Node-RED nor the broker.