Edge App Academy · 3 / 5

Keep credentials with the installation

Make the listener reusable across sites without embedding a password or certificate.

YOUR TASK

Make this happen

3 steps

Add required MQTT_URL, MQTT_USERNAME, MQTT_PASSWORD and MQTT_CA installation settings. Bind broker credentials and TLS CA to them; mark password and CA writeOnly.
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 required MQTT_URL, MQTT_USERNAME, MQTT_PASSWORD and MQTT_CA installation settings. Bind broker credentials and TLS CA to them; mark password and CA writeOnly.

Files to work in

main.cococo, broker.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.

Advertise accepted settings

The installation supplies values validated against configSchema. The definition stores names and contracts, not real credentials.

Secret references

Password and certificate elements take configuration references. Never paste a real password into this browser exercise. ${config:NAME} is a controller binding string, not an IaC resource reference. In a quoted IaC string, write $${config:NAME} to escape IaC interpolation and emit the literal controller binding ${config:NAME}.

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

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]
  mqttBrokers = [edge_app_mqtt_broker.plant]
}

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"
  url = "mqtt://localhost:1883"
  qos = 1
  subscriptions = [edge_app_mqtt_subscription.state]
}

subscription.cococo

edge_app_mqtt_subscription "state" {
  topic = "plant/+/state"
  handler = "receive"
}

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