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))
}

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, 
    };