Lambda Programming Languages

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Overview of Lambda Programming Languages

As we covered in the Lambda Programming Model1 page, Lambda functions run inside a microVM, which is launched with a particular runtime (in crude terms, a programming language environment).

Lambda allows developers to implement custom runtimes2, but also offer a list of execution environments available out-of-the-box. Implementing applications in these ‘default’ environments are the ones this guide is going to cover.

Runtimes and Programming Languages



Developers can run Javascript code in AWS Lambda by using NodeJS environment.

At the time of writing this piece, the NodeJS versions supported were:

  • 12.13.0
  • 10.16.3
  • 8.10

The underlying operating system depends on the version. Lambda uses Amazon Linux 2 for versions 10+ and Amazon Linux 1 for version 8.

Anatomy of a Lambda NodeJS function

By default, the main file in a NodeJS Lambda function is index.js. It should export a function with the name handler. The Lambda environment will passes two arguments to this function:

  • event: contains data about the request and custom information provided by the requester
  • context: provides information about the function and the request context3

The names of the index.js file and handler function can be customized in the AWS Console or through the Lambda CLI.

hello-world NodeJS function in Lambda would be:

Example index.js file:

exports.handler = async function(event, context) {
    console.log('Event: ', event)
    console.log('Remaining time: ', context.getRemainingTimeInMillis())
    console.log('Function name: ', context.functionName)
    return {
        'logStreamName': context.logStreamName

Logging & Debugging

Use the console to log errors, debugging or informational messages in the application:

exports.handler = async function(event, context) {"Event:\n" + JSON.stringify(event, null, 2))
    console.warn("A warning message goes here.")
    console.log("ENV variables:\n" + JSON.stringify(process.env, null, 2))
    return {
        'logStreamName': context.logStreamName

All logs and messages output by the Lambda function will be available in CloudWatch4.

We will soon add here content about Python, Ruby, Java, Go and C# / .NET.


  1. Lambda Programming Model ↩︎
  2. AWS Lambda execution environments and custom runtimes ↩︎
  3. NodeJS context object ↩︎
  4. ↩︎

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