Final answer:
AWS Step Functions is the service that should be used for serverless long running workflows. It allows you to coordinate multiple Lambda functions and other services, making it ideal for complex workflows.
Step-by-step explanation:
The service that should be used for serverless long running workflows is AWS Step Functions. AWS Step Functions is a serverless workflow service that allows you to coordinate multiple Lambda functions and other services to create long running workflows. It provides a visual workflow builder and allows you to express your business logic as a series of steps. With AWS Step Functions, you can build complex workflows and easily track the progress of each step, making it ideal for long running workflows.