Detecting Spoke Failure from Hub using System Tag

Hub Ignition Version: 8.0.15 (64-bit) (Running in Azure Ubuntu VM)
Spoke Ignition Version: 8.1.1 (64-bit) (Running in Docker)

Trying to implement an alarm notification on Hub when there is no communication from Spoke. Particularly interested in utilizing IsAvailable System Tag:

I have an alarm setup to send notification when IsAvailable tag transitions to false.

Here are the tests done to generate the alarm:

1. Shutting down Spoke Ignition Gateway (worked as expected)

Spoke Ignition Gateway was shutdown (stopped the docker container), the alarm was triggered and worked as expected.

2. Disrupt network connection between Hub and Spoke (Did not work as expected)

When connection was disrupted between Hub and Spoke either by disconnecting VPN connection or by blocking port 8060 to Hub - spoke gateway logs show web socket errors but the alarm never gets triggered.

Any thoughts on this and how to utilize IsAvailable Tag?

Does the LastComm tag update when it’s disrupted? Monitoring that may be more effective.

It seems like the IsAvailable System Tag is working, it takes about 12 mins for the Hub to mark the Spoke Ignition as unavailable after the fact. I ended up using Spoke’s system uptime tag as a derived tag on Hub to generate the alarm on stale tag value.