Why can my code run in a standard Node.js file, but not in a AWS Lambda Function?

iii :

What I'm trying to do is create a lambda function where the function calls two commands on an ec2 instance. When I had trouble running this code in a lambda function, I removed the code from the exports.handler() method and ran the code in a standalone node.js file in the same ec2 instance and I was able to get the code to work. The command I ran was 'node app.js'.

exports.handler = async (event) => {

  const AWS = require('aws-sdk')
  AWS.config.update({region:'us-east-1'});

  var ssm = new AWS.SSM();

  var params = {
  DocumentName: 'AWS-RunShellScript', /* required */
  InstanceIds: ['i-xxxxxxxxxxxxxxxx'],
  Parameters: {
    'commands': [
      'mkdir /home/ec2-user/testDirectory',
      'php /home/ec2-user/helloWorld.php'
      /* more items */
    ],
    /* '<ParameterName>': ... */
  }
};
ssm.sendCommand(params, function(err, data) {
  if (err) {
    console.log("ERROR!");
    console.log(err, err.stack); // an error occurred
  }
  else {
  console.log("SUCCESS!");
  console.log(data);
  }            // successful response
});


  const response = {
    statusCode: 200,
    ssm: ssm
  };

  return response;
}; 

I figured that it could have been a permissions related issue, but the lambda is apart of the same vpc that the ec2 instance is in.

Output from the lambda function:

{
  "statusCode": 200,
  "ssm": {
    "config": {
      "credentials": {
        "expired": false,
        "expireTime": null,
        "refreshCallbacks": [],
        "accessKeyId": "xxxxxxxxxxxxxxxxxxxxx",
        "sessionToken": "...",
        "envPrefix": "AWS"
      },
      "credentialProvider": {
        "providers": [
          null,
          null,
          null,
          null,
          null,
          null,
          null
        ],
        "resolveCallbacks": []
      },
      "region": "us-east-1",
      "logger": null,
      "apiVersions": {},
      "apiVersion": null,
      "endpoint": "ssm.us-east-1.amazonaws.com",
      "httpOptions": {
        "timeout": 120000
      },
      "maxRedirects": 10,
      "paramValidation": true,
      "sslEnabled": true,
      "s3ForcePathStyle": false,
      "s3BucketEndpoint": false,
      "s3DisableBodySigning": true,
      "s3UsEast1RegionalEndpoint": "legacy",
      "computeChecksums": true,
      "convertResponseTypes": true,
      "correctClockSkew": false,
      "customUserAgent": null,
      "dynamoDbCrc32": true,
      "systemClockOffset": 0,
      "signatureVersion": "v4",
      "signatureCache": true,
      "retryDelayOptions": {},
      "useAccelerateEndpoint": false,
      "clientSideMonitoring": false,
      "endpointDiscoveryEnabled": false,
      "endpointCacheSize": 1000,
      "hostPrefixEnabled": true,
      "stsRegionalEndpoints": "legacy"
    },
    "isGlobalEndpoint": false,
    "endpoint": {
      "protocol": "https:",
      "host": "ssm.us-east-1.amazonaws.com",
      "port": 443,
      "hostname": "ssm.us-east-1.amazonaws.com",
      "pathname": "/",
      "path": "/",
      "href": "https://ssm.us-east-1.amazonaws.com/"
    },
    "_events": {
      "apiCallAttempt": [
        null
      ],
      "apiCall": [
        null
      ]
    },
    "_clientId": 2
  }
}

Jason Wadsworth :

You're trying to combine async/await with callbacks. That won't work in a lambda AWS Lambda Function Handler in Node.js. The reason it's working locally, or in a node server, is because the server is still running when the function exits, so the callback still happens. In a Lambda the node process is gone as soon as the lambda exits if you are using async (or Promises), so the callback is not able to be fired.