AWS Lambda function example of how to update IoT Thing Shadows

aws-iot-update-thing-shadow-lambda-function.js

const AWS = require('aws-sdk')

AWS.config.region = process.env.AWS_REGION

const AWS_IOT_CORE_ENDPOINT = process.env.MQTT_BROKER_ENDPOINT
const IOT_THING_NAME = process.env.THING_NAME

const iotdata = new AWS.IotData({
    endpoint: AWS_IOT_CORE_ENDPOINT,
})

const openState = "open"
const closedState = "closed"

let currentState = closedState

function toggleGarageDoor(thingName) {
  return new Promise((resolve, reject) => {
    let desiredState = (currentState === closedState) ? openState : closedState
  
    var params = {
      payload: `{"state":{"desired":{"door":"${desiredState}"}}}`,
      thingName: thingName
    }
  
    iotdata.updateThingShadow(params, (err, data) => {
      if (err){
        console.log(err, err.stack)
        reject(`Failed to update thing shadow: ${err.errorMessage}`)
      }else{
        console.log(`update thing shadow response: ${JSON.stringify(data)}`)
        currentState = desiredState
        resolve({"update thing shadow response": data})
      }
    })
  })
}

exports.handler = async (event, context, callback) => {
  await toggleGarageDoor(IOT_THING_NAME)
    .then((result) => callback(null, result))
    .catch((err) => callback(err))
}

@UnHumbleBen I've updated the code to hopefully make it more obvious which environment variables need to be set on your Lambda function. If you aren't setting MQTT_BROKER_ENDPOINT or THING_NAME environment vars on your Lambda, the code won't work.

There was no need to explicitly set the access key pair since AWS Lambda permissions are granted on the Execution Role. The Execution Role must have a policy attached that allows for iot:UpdateThingShadow for the ARN of your AWS IoT Thing, otherwise you will get permissions errors.

Feel free to come back and share any errors you are encountering and I'll see what I can do to help you out.

Thanks @dave-malone !

The fix turned out to be setting a shadowName variable. In my case, I had a thing with multiple shadows, thus a shadowName was necessary to specify which shadow to target. Essentially:

    var params = {
      payload: post_body,
      thingName: process.env.THING_NAME,
      shadowName: process.env.SHADOW_NAME, 
    };