Edge App Academy · 2 / 5

Listen to plant state topics

Bind plant state messages to the receiving handler.

YOUR TASK

Make this happen

3 steps

Add the plant MQTT broker, QoS 1, and plant/+/state subscription routed to receive. Connect mqttBrokers to the document.
Keep the working capabilities from the previous lesson and connect the new pieces to the same solution.
Check the complete solution, then inspect any unmet requirements.

THE IDEA BEHIND IT

What this step adds

Add the plant MQTT broker, QoS 1, and plant/+/state subscription routed to receive. Connect mqttBrokers to the document.

Files to work in

main.cococo, broker.cococo, subscription.cococo. Other files are the working baseline. New files include named resource skeletons and TODO guidance. Complete their fields and connect them using the objectives, schema completion and reference guide.

Topic scope

The + wildcard matches one topic level. This captures each machine’s state topic without subscribing to every broker message.

A temporary address

The localhost broker URL is an illustrative authoring value, never contacted here. Next we replace it with installation configuration so the definition works at different sites.

Checks validate authored native models and lesson connections. No controller, MQTT broker, protocol request, handler or installation is executed.

Files to change: main.cococo, broker.cococo, subscription.cococo

What you’re building: Build a portable plant-state listener whose broker settings and secrets belong to each controller installation.

This step starts with the earlier solution and one new challenge. Each lesson keeps its own draft.

Read the starter files

main.cococo

edge_app_document "main" {
  format = "1"
  handle = "plant-monitor"
  name = "Plant monitor"
  handlers = [edge_app_handler.receive]
}

handlers.cococo

edge_app_handler "receive" {
  name = "receive"
  source = file("scripts/receive.lua")
}

scripts/receive.lua

bridge.log.info(params.topic)
return params.payload

broker.cococo

edge_app_mqtt_broker "plant" {
  name = "plant"
  # TODO: add url — see the task above.
  # TODO: add qos — see the task above.
  # TODO: add subscriptions — see the task above.
}

subscription.cococo

edge_app_mqtt_subscription "state" {
  # TODO: add topic — see the task above.
  # TODO: add handler — see the task above.
}

Supplied supporting files

Reference: edge-apps · getting-started edge-apps · definitions edge-apps · scripts-triggers edge-apps · mqtt-opcua edge-apps · industrial edge-apps · exec-http edge-apps · diagnostics edge-apps · reference