Amazon Lambda also supports to run custom code referred as Lambda function by directly inputting your code or uploading a compressed ZIP file of the code in order to run your application code. Amazon Lambda processes your Lambda functions in response to events, for example, the object-created events in S3 bucket, the DynamoDB table updates, or JSON inputs or HTTP commands from your application.

We will be creating a sample Node.js. S3 notifies an event to AWS Lambda and AWS Lambda invokes a Lambda function, which then creates a thumbnail and saves it to a target bucket when the objects (image files) are uploaded into a source bucket. The following screenshot shows the sample application architecture composed of a Lambda function, IAM role, and S3 bucket.