How to test AWS Lambda handler locally using NodeJS?

Question

I am following these instructions to create a basic web scraper that executes in Lambda. I have experience writing selenium code, but not with Node JS. I got the project running in Lambda, but when I tried editing the project locally in order to execute the selenium code I want, It doesn't work. Anything in the exports.handler doesn't get executed when I run node index.js. How would I execute this project locally? Thanks!

Answer 1

This is what I did:

index.js

exports.handler = async (event) => {
    console.log('hello world');

    const response = {
        statusCode: 200,
        body: JSON.stringify('Hello from Lambda!')
    };

    return response;
};

package.json

"scripts": {
  "locally": "node -e \"console.log(require('./index').handler(require('./event.json')));\""
}

event.json

{
  "Records": [
    {
      "eventVersion": "2.0",
      "eventSource": "aws:s3",
      "awsRegion": "eu-central-1",
      "eventTime": "1970-01-01T00:00:00.000Z",
      "eventName": "ObjectCreated:Put",
      "userIdentity": {
        "principalId": "AIDAJDPLRKLG7UEXAMPLE"
      },
      "requestParameters": {
        "sourceIPAddress": "127.0.0.1"
      },
      "responseElements": {
        "x-amz-request-id": "C3D13FE58DE4C810",
        "x-amz-id-2": "FMyUVURIY8/IgAtTv8xRjskZQpcIZ9KG4V5Wp6S7S/JRWeUWerMUE5JgHvANOjpD"
      },
      "s3": {
        "s3SchemaVersion": "1.0",
        "configurationId": "testConfigRule",
        "bucket": {
          "name": "my-bucket",
          "ownerIdentity": {
            "principalId": "A3NL1KOZZKExample"
          },
          "arn": "arn:aws:s3:::my-bucket"
        },
        "object": {
          "key": "HelloWorld.jpg",
          "size": 1024,
          "eTag": "d41d8cd98f00b204e9800998ecf8427e",
          "versionId": "096fKKXTRTtl3on89fVO.nfljtsv6qko"
        }
      }
    }
  ]
}

Shell

npm run locally

Output

> node -e "console.log(require('./index').handler({}));"

hello world
Promise { { statusCode: 200, body: '"Hello from Lambda!"' } }

Answer 2

You need to call your handler function from another file lets say testHandler.js in order to run via NodeJs.

This will be done like this

//import your handler file or main file of Lambda
let handler = require('./handler');

//Call your exports function with required params
//In AWS lambda these are event, content, and callback
//event and content are JSON object and callback is a function
//In my example i'm using empty JSON
handler.handlerEvent( {}, //event
    {}, //content
    function(data,ss) {  //callback function with two arguments 
        console.log(data);
    });

Now you can use node testHandler.js to test your handler function.

EDIT: Sample Event and content data as requested

Event:

{
    "resource": "/API/PATH",
    "path": "/API/PATH",
    "httpMethod": "POST",
    "headers": {
        "Accept": "*/*",
        "Accept-Encoding": "gzip, deflate, br",
        "Accept-Language": "en-GB,en-US;q=0.9,en;q=0.8",
        "cache-control": "no-cache",
        "CloudFront-Forwarded-Proto": "https",
        "CloudFront-Is-Desktop-Viewer": "true",
        "CloudFront-Is-Mobile-Viewer": "false",
        "CloudFront-Is-SmartTV-Viewer": "false",
        "CloudFront-Is-Tablet-Viewer": "false",
        "CloudFront-Viewer-Country": "IN",
        "content-type": "application/json",
        "Host": "url.us-east-1.amazonaws.com",
        "origin": "chrome-extension://fhbjgbiflinjbdggehcddcbncdddomop",
        "User-Agent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36",
        "Via": "2.0 XXXXXXXXXXXXXX.cloudfront.net (CloudFront)",
        "X-Amz-Cf-Id": "XXXXXXXXXX51YYoOl75RKjAWEhCyna-fuQqEBjSL96TMkFX4H0xaZQ==",
        "X-Amzn-Trace-Id": "Root=1-XXX03c23-25XXXXXX948c8fba065caab5",
        "x-api-key": "SECUREKEY",
        "X-Forwarded-For": "XX.XX.XXX.XXX, XX.XXX.XX.XXX",
        "X-Forwarded-Port": "443",
        "X-Forwarded-Proto": "https"
    },
    "multiValueHeaders": {
        "Accept": [ "*/*" ],
        "Accept-Encoding": [ "gzip, deflate, br" ],
        "Accept-Language": [ "en-GB,en-US;q=0.9,en;q=0.8" ],
        "cache-control": [ "no-cache" ],
        "CloudFront-Forwarded-Proto": [ "https" ],
        "CloudFront-Is-Desktop-Viewer": [ "true" ],
        "CloudFront-Is-Mobile-Viewer": [ "false" ],
        "CloudFront-Is-SmartTV-Viewer": [ "false" ],
        "CloudFront-Is-Tablet-Viewer": [ "false" ],
        "CloudFront-Viewer-Country": [ "IN" ],
        "content-type": [ "application/json" ],
        "Host": [ "apiurl.us-east-1.amazonaws.com" ],
        "origin": [ "chrome-extension://fhbjgbiflinjbdggehcddcbncdddomop" ],
        "User-Agent": [ "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36" ],
        "Via": [ "2.0 XXXXXXXXXXXXXX.cloudfront.net (CloudFront)" ],
        "X-Amz-Cf-Id": [ "XXXXXXXXXhCyna-fuQqEBjSL96TMkFX4H0xaZQ==" ],
        "X-Amzn-Trace-Id": [ "Root=1-XXXXXXX67339948c8fba065caab5" ],
        "x-api-key": [ "SECUREAPIKEYPROVIDEDBYAWS" ],
        "X-Forwarded-For": [ "xx.xx.xx.xxx, xx.xxx.xx.xxx" ],
        "X-Forwarded-Port": [ "443" ],
        "X-Forwarded-Proto": [ "https" ]
    },
    "queryStringParameters": null,
    "multiValueQueryStringParameters": null,
    "pathParameters": null,
    "stageVariables": null,
    "requestContext": {
        "resourceId": "xxxxx",
        "resourcePath": "/api/endpoint",
        "httpMethod": "POST",
        "extendedRequestId": "xxXXxxXXw=",
        "requestTime": "29/Nov/2018:19:21:07 +0000",
        "path": "/env/api/endpoint",
        "accountId": "XXXXXX",
        "protocol": "HTTP/1.1",
        "stage": "env",
        "domainPrefix": "xxxxx",
        "requestTimeEpoch": 1543519267874,
        "requestId": "xxxxxxx-XXXX-xxxx-86a8-xxxxxa",
        "identity": {
            "cognitoIdentityPoolId": null,
            "cognitoIdentityId": null,
            "apiKey": "SECUREAPIKEYPROVIDEDBYAWS",
            "cognitoAuthenticationType": null,
            "userArn": null,
            "apiKeyId": "xxXXXXxxxxxx",
            "userAgent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/68.0.3440.106 Safari/537.36",
            "accountId": null,
            "caller": null,
            "sourceIp": "xx.xxx.xxx.xxx",
            "accessKey": null,
            "cognitoAuthenticationProvider": null,
            "user": null
        },
        "domainName": "url.us-east-1.amazonaws.com",
        "apiId": "xxxxx"
    },
    "body": "{\n    \"city\": \"Test 1 City\",\n    \"state\": \"NY\",\n    \"zipCode\": \"11549\"\n}",
    "isBase64Encoded": false
}

Content:

{
    "callbackWaitsForEmptyEventLoop": true,
    "logGroupName": "/aws/lambda/lambda-name",
    "logStreamName": "2018/11/29/[$LATEST]xxxxxxxxxxxb",
    "functionName": "lambda-name",
    "memoryLimitInMB": "1024",
    "functionVersion": "$LATEST",
    "invokeid": "xxxxx-xxx-11e8-xxx-xxxxxxxf9",
    "awsRequestId": "xxxxxx-xxxxx-11e8-xxxx-xxxxxxxxx",
    "invokedFunctionArn": "arn:aws:lambda:us-east-1:xxxxxxxx:function:lambda-name"
}

Answer 3

In your index.js, just defined and exported a handler function, but no one calls it. In the Lambda environment, some AWS code will call this handler with message. In your local environment, you have to call your handler by yourself.

You could also have a look of this doc, it is a way to "simulate" Lambda in local environment.

Answer 4

Perhaps the simplest way to get started, after some testing (with Node 14.17.3)

let handler = require('./index.js');

handler.handler ( 
  {}, // event
  {}, // content 
  (error, result) => { 
     if (error) console.error(JSON.stringify(error, null, 2));
     else console.log(JSON.stringify(result, null, 2));
  }
);