What is AWS Lambda?

AWS Lambda is a Function-as-a-service (FaaS) computing platform provided by Amazon Web Services (AWS). As a FaaS, it provides a computing platform to execute code in the cloud. As in any serverless system, it abstracts away the complexities of provisioning and managing a cloud infrastructure.

It is commonly used when building microservices applications, but also serves monolithic and other types of architectures as well. There are several use cases and multiple benefits from using AWS Lambda.

Lambda execution environment and available runtimes

  • Container with a 64-bit Amazon Linux AMI1
  • RAM: 128MB to 3008MB, in 64 MB increments
  • CPU increases incrementally with RAM2
  • Execution duration: up to 900 seconds (or 15 minutes)
  • Ephemeral disk space 512MB
  • Compressed package size 50MB
  • Uncompressed package size 250MB

Lambda supports the following runtimes by default:

  • Node.js: v10.15 and v8.10
  • Java 8
  • Python: 3.7, 3.6, and 2.7
  • .NET Core: 1.0.1 and 2.1
  • Go 1.x
  • Ruby 2.5
  • Rust

Developers can implement any other custom runtime of their choosing. The custom runtime will run in the Lambda execution environment. It can be a shell scrit or an executable binary3.

Anatomy of a Lambda function

All Lambda functions consist of three key elements:

  • Handler function
    • The main function that will be executed each time an event occurs.
    • Takes two required arguments: an event and context objects (also takes an optional callback object)
  • Event Object
    • The first argument to the handler function
    • Contains information about the invocation event
    • An invocation event could be an API request event holding the HTTP request object, for example
  • Context object
    • Contains information about the Lambda runtime, such as the function name, version, memory limit, etc.4
    • Provides a method that returns the remaining miliseconds left before the function times out

AWS Lambda pricing and free tier

Lambda functions are billed by the time it takes to execute your function, being rounded up to the nearest 100ms and the GB-seconds based on the memory consumption. It also comes with a free tier of 1 million requests and 400,00 GB-seconds of compute time each month.

After the free tier, it costs $0.20 per 1 million requests and $0.00001667 for every GB-seconds. The GB-seconds is based on the memory consumption of the Lambda function. For further details check out the Lambda Pricing Page or the Lambda Cost Calculator.


  1. AWS Lambda Runtimes ↩︎
  2. At 1,792 MB, a function has the equivalent of 1 full vCPU (one vCPU-second of credits per second) ↩︎
  3. Custom AWS Lambda Runtimes documentation ↩︎
  4. More info about the AWS Lambda Context Object in PythonNodeJSJAVAGolang, and C# ↩︎