Hello,
Is there a way to get the information when needed on whether the MQTT IN or OUT node is effectively connected ?
I know about the status node, however, the value is changed only when an "event" (connection, disconnection) occurs.
I would like to be able to query a value when I need it and not when it changes ?
Is that doable ? Or should I plug the status to change and a flow variable to store the value ?
Thanks !
That is the most effective way. It will get populated when Node-RED starts and the connection is created. It is only when you first add the status node and deploy using NON full deploy that it misses the first event.
Alternatively, you could set the broker to NOT auto connect & issue a connect action yourself
Additionally, you can make use of LWT (Last Will and Testament) topics
Finally, the better solution is to do this end-2-end: Subscribe to a known changing topic (check the $ system variables your broker outputs.) Or, sub & pub a timestamp to a random topic (e.g. _/mqtt/heartbeat and use the trigger node to watch for the expected changes. If non arrives, connection can be considered "bad"
NOTE: the MQTT IN and OUT nodes do NOT connect. The connection is made via the config node. Watching either is the same (they are both updated by the broker config node)
Yes, you are correct.
I am effectively monitoring the config node or at least the node where my dynamic configuration is done.
Unfortunately, I can't use the heartbeat or the $SYS as I don't have write access or access to $SYS topic.
I am dealing with external (not managed by me) brokers.
It looks like my best option is to store the status in a variable...
Thanks.
Note though that there can be a delay before Disconnected is shown.
What do you mean ?
The "status" is updated immediately.
If the network connection fails then there will be a delay before it shows disconnected.
If you are manually connecting and disconnecting the broker then why do you need to use the status, as you already know whether it is disconnected or not?
Perhaps I'm missing something but can't you do this on demand by sending a message and watching for [lack of a] response?
In this example a delay of 5 seconds is taken as MQTT is not effectively connected, but you can clearly tweek this to balance slow connections and speed of detecting an outage.
I am manually attempting to connect. However, it may fail when trying to connect or fail later if the remote MQTT has an issue.
And I have some edge case, where the MQTT is effectively connected, but the status is not updated, or my flow misses it somehow. I am trying to figure out why. While doing so having the option to "query" the situation, could have been handy.
I have no write (publish) access to the remote broker. Only read (subscribe) ...
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See also this issue, I found that it could sometimes take up to 16 minutes to show disconnected. MQTT node may not show disconnected for a long time when network is disconnected · Issue #4509 · node-red/node-red · GitHub
I there anything that you expect to come in at a known rate? If so you could use the fact that it is not coming in to tell you there is a problem.
Not really. It is irregular.
I can use arrival of messages to confirm it is connected. But, non arrival is not a guarantee of being disconnected.
What type of errors are you envisaging? If it is network failure then you may be able to ping the server and would then know within a few seconds when a failure occurs.
Not possible to ping either. Only port 8883 and only subscribe.
This is why being able to query the connection status was looking like a good option. Unfortunately, not doable.
It is doable, but it may be slow to tell you it is offline.
