Question 1

What's the difference between Step Functions and AWS Lambda?

Accepted Answer

AWS Lambda runs your code in response to events (a single function execution). Step Functions coordinates multiple steps—often multiple Lambda functions plus other AWS services—into a workflow with ordering, branching, retries, timeouts, and a visual execution history. In practice, Lambda is a building block; Step Functions is the orchestrator.

Question 2

When should I use Step Functions?

Accepted Answer

Use Step Functions when your process has multiple steps that must be coordinated reliably—especially if you need branching logic, parallel work, human approvals, retries, timeouts, or long-running workflows. Common cases include order processing, ETL/data pipelines, media processing, ML pipelines, account onboarding, and incident/ops runbooks. If your task is a single short action, a single Lambda (or a queue + worker) may be enough.

Question 3

How much does Step Functions cost?

Accepted Answer

Pricing is based on how many state transitions your workflows perform and which workflow type you use. Standard Workflows typically charge per state transition and are designed for long-running, durable workflows with exactly-once execution. Express Workflows are designed for very high-throughput, short-duration workflows and are priced based on the number of requests and compute/time used. Your total cost also includes the services you orchestrate (e.g., Lambda invocations, DynamoDB reads/writes, SNS/SQS, etc.).

Step Functions

Definition

Real-World Example

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