Creating a lambda function in AWS from zip file

I am trying to create a simple lambda function, and I'm running into an error.

My code is basically

console.log('Loading function');

exports.handler = function(event, context) {
    console.log('value1 =', event.key1);
    console.log('value2 =', event.key2);
    console.log('value3 =', event.key3);
    context.succeed(event.key1);  // Echo back the first key value
    // context.fail('Something went wrong');
}

in a helloworld.js file. I zip that up and upload it as a zip file in the creating a lambda function section, and I keep getting this error:

{
  "errorMessage": "Cannot find module 'index'",
  "errorType": "Error",
  "stackTrace": [
    "Function.Module._resolveFilename (module.js:338:15)",
    "Function.Module._load (module.js:280:25)",
    "Module.require (module.js:364:17)",
    "require (module.js:380:17)"
  ]
}

Anyone have any ideas?