AWS Step Functions: Standard vs Express workflows, retry/catch, task tokens for callbacks

AWS Step Functions is a serverless orchestration service. You describe a workflow as a state machine in Amazon States Language (ASL), a JSON-based format, and Step Functions runs it: calling Lambda functions and other AWS services, passing data between steps, waiting, branching and handling errors. Because the workflow's logic lives in the state machine rather than in your code, each Lambda function stays small and the console shows every execution visually, step by step.