Lambda: Publish a MQTT Message to IOT Core inside a Lambda function with Node and SDK 3

I do not know why but this worked for me now. If anyone can explain, feel free to do so :)

const { IoTDataPlaneClient, PublishCommand } = require('@aws-sdk/client-iot-data-plane');

exports.handler = async (event) => {
  const client = new IoTDataPlaneClient({ region: 'eu-west-1' });
  const payload = { message: 'Hello from Lambda!' };
  const topic = 'mytopic/test';

  const publishCommand = new PublishCommand({
    topic,
    payload: JSON.stringify(payload),
    qos: 0,
  });

  try {
    await client.send(publishCommand);
  } catch (error) {
    console.error(error);
  }
};

Hello, I can give you a code snippet. The following program uses my local computer's config and credentials, which can send messages to the AWS IoT Core and has passed the test

my nodejs version is v18.17.0

const {IoTDataPlaneClient, PublishCommand} = require('@aws-sdk/client-iot-data-plane');

/**
 * send message to AWS IoT Core topic
 * @param topicName
 * @param message
 * @returns {Promise<PublishCommandOutput>}
 */
async function awsIoTCoreMqttPublisher(topicName, message) {
    // https://docs.aws.amazon.com/sdk-for-javascript/v3/developer-guide/getting-your-credentials.html
    // https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/iot-data-plane/
    const client = new IoTDataPlaneClient({
        region: 'us-east-1',
        // optional
        // endpoint: "my-endpoint.eu-west-1.amazonaws.com",
    });
    // https://docs.aws.amazon.com/AWSJavaScriptSDK/v3/latest/client/iot-data-plane/command/PublishCommand/
    const publishCommand = new PublishCommand({
        topic: topicName,
        payload: JSON.stringify(message),
        qos: 0,
    });

    return client.send(publishCommand);
}

// ---------------- test ----------------
// test topic
const topicName = "mytopic/test";
// test message
const message = {
    "@aws-sdk/client-iot": "^3.454.0",
    "@aws-sdk/client-iot-data-plane": "^3.454.0",
    "message": "Hi from lambda",
}
// publish message to topic
const p = awsIoTCoreMqttPublisher(topicName, message)
p.then(
    result => console.log("httpStatusCode:", result.$metadata.httpStatusCode),
    err => console.log("rejected: ", err)
)

run this javascript file you can use AWS IoT Core MQTT test client subscription topic and then you can see message

This JS program works and have "publish" permission in your lamda's policy

import { IoTDataPlaneClient, PublishCommand } from "@aws-sdk/client-iot-data-plane";
const client = new IoTDataPlaneClient({ region: 'us-east-1' });

export const handler = async (event) => {  
  const topic = '$aws/things/myDHT/shadow/name/shadow_1/update';  
  const message = {
                    "state": {
                      "desired": {
                        "welcome": "aws-iot"
                      },
                      "reported": {
                        "welcome": "aws-iot",
                        "thing_name": "myDHT",
                        "date": "20240220",
                        "time": "112101",
                        "humidity": 55.20000076,
                        "temperature": 31.39999962
                      }
                    }
};  

  const publishCommand = new PublishCommand({
    topic,
    payload: JSON.stringify(message),
    qos: 0,
  });  

  try {
    const data = await client.send(publishCommand);
    console.log(data);
  } catch (error) {
    console.error(error);
  }
};