Question

Why are AWS Lambda function stateless? Is there a particular reason for the necessity of Lambda function being stateless?

Answer 1

Keeping functions stateless enables AWS Lambda to rapidly launch as many copies of the function as needed to scale to the rate of incoming events. While AWS Lambda’s programming model is stateless, your code can access stateful data by calling other web services, such as Amazon S3 or Amazon DynamoDB. You can read more about why to form your lambda function in a stateless way here:-
https://docs.aws.amazon.com/lambda/latest/dg/programming-model-v2.html