AWS Lambda - How It Works http://docs.aws.amazon.com/lambda/latest/dg/lambda-introduction.html
AWS Lambda environment variables http://docs.aws.amazon.com/lambda/latest/dg/current-supported-versions.html
What's callback and how to deal with it http://docs.aws.amazon.com/lambda/latest/dg/nodejs-prog-model-handler.html#nodejs-prog-model-handler-callback