The MQTT modules (MQTT Transmission, MQTT Distributor and MQTT Engine) all provide status tags within Ignition that can be used to monitor the overall health of the MQTT pipeline.

MQTT Engine

The tags automatically created for MQTT Engine are documented here

Engine Info - Edge Nodes

MQTT Modules for Ignition 8.x > Monitoring overall MQTT Pipeline Health > image-2024-6-3_16-32-59.png

Use the tags below to verify the expected number of Edge Nodes have come online and remain online:

NodesOffline	Integer	The number of Sparkplug Edge Nodes offline. This is determined by whether the last lifecycle message was an NBIRTH or NDEATH
NodesOnline	Integer	The number of Sparkplug Edge Nodes online. This is determined by whether the last lifecycle message was an NBIRTH or NDEATH
NodeUnitCount	Integer	The total number of Sparkplug Edge Nodes as determined by the received NBIRTH messages

Use the tags below to identify the Sparkplug ID and last timestamp for the Offline and Online nodes

Offline Nodes	Dataset	A dataset containing the Sparkplug ID and timestamp for all offline Sparkplug edge nodes
Online Nodes	Dataset	A dataset containing the Sparkplug ID and timestamp for all online Sparkplug edge nodes

Use the script below to easily parse the Offline and Online datasets

onlineEdgeNodes = system.dataset.toPyDataSet(system.tag.readBlocking("[MQTT Engine]Engine Info/Edge Nodes/Online Nodes")[0].value)     
print "Online Sparkplug EdgeNodes: " + str(system.tag.readBlocking("[MQTT Engine]Engine Info/Edge Nodes/NodesOnline")[0].value)
if system.tag.readBlocking("[MQTT Engine]Engine Info/Edge Nodes/NodesOnline")[0].value > 0:
    for row in onlineEdgeNodes:
        data = []
        data.append(["Sparkplug EdgeNode Descriptor", row[0]])
        data.append(["Last Connect Date", row["Date"]])
        print data
         
offlineEdgeNodes = system.dataset.toPyDataSet(system.tag.readBlocking("[MQTT Engine]Engine Info/Edge Nodes/Offline Nodes")[0].value)     
print "Offline Sparkplug EdgeNodes: " + str(system.tag.readBlocking("[MQTT Engine]Engine Info/Edge Nodes/NodesOffline")[0].value)
if system.tag.readBlocking("[MQTT Engine]Engine Info/Edge Nodes/NodesOffline")[0].value > 0:
    for row in offlineEdgeNodes:
        data = []
        data.append(["Sparkplug EdgeNode Descriptor", row[0]])
        data.append(["Last Connect Date", row["Date"]])
        print data

Engine Info - MQTT Clients

MQTT Modules for Ignition 8.x > Monitoring overall MQTT Pipeline Health > image-2024-6-3_16-57-52.png

Server Latency (ms)

Integer

The amount of time that it takes for a test MQTT message to be sent and received back by MQTT Engine

Edge Node - Node Info Tags

For each connected Edge Node, a Node Control and Node Info folder containing tags is created along with a Device Info folder for each connected device.

MQTT Modules for Ignition 8.x > Monitoring overall MQTT Pipeline Health > EngineEdgeNodeInfoTags.png

Using these tags we can look into the health of each Edge Node connection:

Data Latency (ms)

Long

The time in milliseconds between MQTT Engine receiving of the last message and the payload's reported time.

A long latency time can indicate network issues.

Note: For this to be very accurate the edge node's clock and the system clock running MQTT Engine should be synced

Birth Count

Long

The number of NBIRTH messages since the last time the info metrics were reset via the Node Info/Reset Info tag

Death Count

Long

The number of NDEATH messages since the last time the info metrics were reset via the Node Info/Reset Info tag

Offline DateTime

DateTime

The time at which the last NDEATH message was received by MQTT Engine

Online

Boolean

Whether or not the Edge Node is online. This is determined by whether the last lifecycle message was an NBIRTH or NDEATH

Online DateTime

DateTime

The time at which the first NBIRTH message for a connection was received by MQTT Engine

Rebirth Count

Integer

The count of rebirth requests issued by MQTT Engine (available 4.0.22 onward)

A high rebirth count in a small time window is a clear indicator of issues at the Edge(s)

Rebirth (Last DateTime)

DateTime

The time of the last rebirth request issued by MQTT Engine (available 4.0.22 onward)

Rebirth (Last) Cause

String

The reason for the last rebirth request (available 4.0.22 onward)

Reasons for rebirth requests are:

Triggered by user
- A rebirth request for the Edge Node was manually triggered at MQTT Engine

Message sequence number error

The message sequence number received was not in order

In a Sparkplug compliant system, the combination of Group ID and Edge Node ID (the Sparkplug Edge Node Descriptor) that identifies the Edge Node must be unique. If there are two or more Transmitters with the same Sparkplug Edge Node Descriptor, data from these two transmitters will sent with the same topic resulting in the next message sequence number expected by the MQTT client being incorrect. As a result, the MQTT Client will mark the data as stale and request a rebirth from the transmitter.

If you have multiple MQTT Clients subscribing to the namespace, this will also likely create a firestorm of rebirth requests across the system.

Received a message for an edge node that is offline
- An NDATA message was received from an Edge Node that is marked as Offline at MQTT Engine.
Reordering sequence numbers
- The message sequence number received was not in order after waiting the specified number of milliseconds after receiving an out of order message for the expected message to arrive.
Unable to set Edge Node online
Failed to find metric name from alias
- The alias in the DATA message did not match any alias previously published in the BIRTH message
UDT tag doesn't exist
Unknown metric
DDATA before BIRTH
- An DDATA message was received from an Edge Node Device that is marked as Offline at MQTT Engine.