SAP-C02 Practice Question 76: Express Workflow High Volume Idempotent

AWS Certified Solutions Architect – Professional (SAP-C02) · Test 8 · question 6 of 10

Design for New Solutionseasy

An IoT platform processes about 50,000 sensor messages per second. For each message, a workflow validates the payload, calls two Lambda functions and writes an item to DynamoDB with a PutItem call keyed by the message ID. Each execution finishes in under 10 seconds. The team currently uses AWS Step Functions Standard workflows, and the state transition charges have become the largest part of the bill. An occasional duplicate execution is harmless.

Which change reduces cost while meeting the requirements?

Show answer and explanation

Answer:

B. Rebuild the workflow as an Express workflow

Express workflows *"are ideal for high-volume, event-processing workloads such as IoT data ingestion, streaming data processing and transformation,"* and they can run up to five minutes. They are billed *"by number of executions, total duration of execution, and memory consumed"*, whereas Standard workflows are billed by the number of state transitions. Express workflows use an at-least-once model, *"better suited for orchestrating idempotent actions, such as transforming input data to store in Amazon DynamoDB using a PUT action"*, which matches this workload (option B).

- A is wrong because Distributed Map is a Standard-only feature for large-scale parallel processing. It adds transitions and is not a fit for millions of tiny independent messages. - C is wrong because merging two functions saves one transition per execution but still leaves the per-transition pricing model at 50,000 executions per second. - D is wrong because chaining Standard workflows adds more transitions and more events, which increases cost.

Reference: Choosing workflow type in Step Functions

Practice Test 8 ›

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