AWS IoT Greengrass Nodes

The Greengrass Publish node sends a message to a topic on a Greengrass core device's local broker. Greengrass components on the core receive it directly, other client devices subscribed to the topic receive it, and the core's MQTT bridge can relay it to AWS IoT Core. Because the broker runs on the plant network, the node keeps working while the site's internet connection is down.

Configuration Quick Reference

Field	What you choose	Details
Parameters	Connection, Function, Function Parameters, Timeout Override	Select the Greengrass connection, a Publish Message function, fill its ((parameters)) with expressions, and optionally override the timeout.
Settings	Description, Timeout (seconds), Retry on Timeout, Retry on Fail, On Error	Node description, maximum execution time, retry behavior and error handling. All execution settings default to pipeline-level values.

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AWS IoT Greengrass Publish Node

AWS IoT Greengrass Publish Node

Supported Function Types:

Function Name	Purpose	Common Use Cases
Publish Message	Send a payload to a topic on the core device's local broker	Edge KPIs for local components, alarms relayed to AWS IoT Core, commands to other client devices

How It Works

1. The node resolves the function's ((parameters)) from its Function Parameters.
2. It publishes the payload on the connection's live session with the core, at the function's QoS.
3. At QoS 1 it waits for the broker's PUBACK before completing.

If the core cannot be reached, for example while it restarts after a Greengrass deployment, the publish fails as a retryable error and Store & Forward holds the message until the connection is back. A wildcard in the topic, or an empty payload, fails the node at once and is not retried.

Configuration

Field	What you choose	Details
Connection	Greengrass connection profile	A connection set up as a client device of the core, see the connection guide
Function	Publish Message function	Defines the topic, payload, QoS and retain flag
Function Parameters	Values for ((name)) placeholders	Literal values or {{ }} expressions over upstream data

For the function fields, see Publish Message Function.

Starting a pipeline from local messages

To run a pipeline whenever a message arrives on the core's broker, use the AWS IoT Greengrass Trigger.

Output

The broker's acknowledgement is delivered under result; execution facts (success, functionId, durationMs, timestamp) under _metadata.

Expression	Description
$node["Name"].result.topic	The local topic the message was published to
$node["Name"].result.bytesWritten	Payload size in bytes
$node["Name"].result.qos	The QoS the message was sent with (0 or 1)
$node["Name"].result.retained	Whether the core's broker stored it as the topic's retained message
$node["Name"]._metadata.method, $node["Name"]._metadata.connectionId, $node["Name"]._metadata.protocol	The call's own facts: the operation, the connection it ran over, greengrass

{
  "result": {
    "topic": "factory/line3/oee",
    "bytesWritten": 13,
    "qos": 1,
    "retained": false
  }
}