You have an existing AWS setup with DirectConnect. You have migrated certain on premise backend applications to AWS EC2 instances which are having certain processes run based on triggers from other applications. These processes are developed on JAVA programming language. Your organization is looking to migrate these processes to Lambda and reduce the cost incurred on EC2 instances. What would be your recommendation?

Answer options:

A.AWS Lambda cannot be invoked from a custom application. They can only be triggered by AWS supported event sources.
B.Replicate the JAVA code easily onto AWS Lambda function with few modifications and use Lambda Invoke API with input passed as custom event.
C.Trigger Lambda from AWS CloudWatch scheduled event and invoke CloudWatch API from your applications.
D.AWS Lambda is not designed to run backend applications. Better to use EC2 for that purpose.

Answer: B
You can invoke a Lambda function using a custom event through AWS Lambda’s invoke API. Only the function’s owner or another AWS account that the owner has granted permission can invoke the function.
https://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html
https://docs.aws.amazon.com/lambda/latest/dg/with-userapp.html