Testing Lambda Durable Functions Locally with LocalStack

AWS Lambda Durable Functions, released in late 2025, allow long-running, stateful workflows to remain in a single Lambda handler by checkpointing completed steps and replaying execution after retries, waits, callbacks, crashes, or interruptions. The tutorial demonstrates building an order-processing workflow with Python, CDK, DynamoDB, SNS, and SQS, in which an order is validated and recorded, payment is retried with exponential backoff, an external payment-confirmation callback pauses the workflow, notifications are sent in parallel, and the order is marked fulfilled. LocalStack 2026.8.0 or later supports durable-function creation, execution management, retries, callbacks, parallel branches, history, idempotent execution names, and persistent state, enabling developers to test recovery scenarios locally. The example deploys a production-ready package containing the durable execution SDK, starts a named execution, verifies that failed payment attempts cause separate invocations while completed steps are skipped on replay, restarts LocalStack while the execution awaits a callback, and confirms that persisted checkpoints allow the workflow to resume successfully. After a callback is sent, the execution completes with a fulfilled status, records the charge and confirmation in DynamoDB, and produces email and SMS notifications, illustrating fault-tolerant workflow behavior without a separate Step Functions state machine.

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