AWS Lambda durable functions extend the Lambda programming model with built-in capabilities for fault-tolerant, long-running workflows. Checkpoint progress, recover from failures, and suspend execution for up to one year — all without compute charges. You write sequential code in your preferred language, and the open source durable execution SDK handles checkpointing, retries, and state management automatically.

Durable functions introduce two core primitives: Steps (context.step()) for automatic retries and checkpointing, and Waits (context.wait()) for suspending execution without compute charges. Additional operations include waitForCallback() for human-in-the-loop approvals, waitForCondition() for polling, and parallel() or map() for concurrency patterns.

Durable functions currently support Python, Node.js (JavaScript/TypeScript), and Java runtimes, and integrate with existing Lambda event sources, AWS SAM, AWS CDK, CloudFormation, and Terraform.