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AWS Greengrass Core SDK for JavaScript

The AWS Greengrass Core SDK for JavaScript allows developers to write JavaScript Lambda functions which will run within Greengrass.

Overview

This document provides instructions for preparing your Greengrass Core environment to run Lambda functions written in JavaScript. It also includes examples on how to develop a Lambda function in JavaScript as well as packaging and running an example Hello World file in JavaScript for your Greengrass core.

Preparing your Greengrass to run NodeJS Lambda functions

The environment where Greengrass is running on needs to be able to run NodeJS 12.x applications.

• Install NodeJS 12 for your platform. You can download the newest NodeJS from https://nodejs.org/en/download/.
• When you untar the package downloaded from NodeJS website, you will find node file under bin directory.
• Copy the file to /usr/bin or /usr/local/bin folder.
• Rename the file to nodejs12.x

Getting Started - Hello World

• Copy samples/HelloWorld folder to your workspace.
• Create a folder node_modules under HelloWorld folder.
• Unzip aws-greengrass-core-sdk-js.zip into the folder. It should create a folder HelloWorld/node_modules/aws-greengrass-core-sdk
• Use NPM to install the required dependency, cbor. npm i cbor@5.0.1.
• Zip up the content of HelloWorld folder so that the index.js is on the top of the zip file structure.
• Go to AWS Lambda Console.
• Create a new function.
• Choose the Runtime as Node.js 12.x
• Upload the zip file in Lambda function code section.
• Handler is index.handler
• Choose any role as the role is not used within Greengrass.
• After creating the function, publish the Lambda.
• Create an Alias and point to the Published version (not $LATEST).
• Go to your Greengrass Group and add the Lambda under Lambdas section.
• Click on the Lambda and change the Lambda lifecycle to Make this function long-lived and keep it running indefinitely.
• Add a Subscription with the following configuration:
  • Source: Lambda which you just created and added to the group
  • Target: IoT Cloud
  • Topic: hello/world
• Deploy. A message from your Lambda should be published to the topic hello/world in the cloud every 5 seconds. You can check this by going to AWS IoT's Test page and subscribing to topic hello/world.

Including aws-greengrass-core-sdk with your function

Unzip the SDK into your node_modules folder of your function. This should create a aws-greengrass-core-sdk folder which includes the SDK.

Logging in NodeJS Lambdas

Your console.log operation will be logged as INFO. A console.error operation will be logged as ERROR. Currently, our NodeJS SDK only allows you to log at INFO or ERROR level only.

Supported Datatypes

From GGC version 1.5, you can send both JSON and binary data as a payload when you invoking other Lambdas or publishing a message using IotData service. In order to make your lambda be able to handle binary payload, you need to configure the lambda in Greengrass console to mark it using binary input payload so that GGC can know how to deal with the data.

Supported Context

In Greengrass, you can send a context object in a JSON format to be passed to another Lambda that is being invoked. The context format looks like this: { custom: { customData: 'customData', }, }

const {
    StreamManagerClient
} = require('aws-greengrass-core-sdk').StreamManager;

const c = new StreamManagerClient({
    onConnectCb: async () => {
        try {
            // Let's start with something simple.
            // Just print out all the available stream names on the server 
            console.log(await c.listStreams());
        } finally {
            c.close(); // Always close the client when you're done
        }
    }
});

Getting Help

• Ask on a Greengrass forum

License

Apache 2.0