aws-lambda-durable-functions

AWS Lambda durable functions

Build resilient multi-step applications and AI workflows that can execute for up to 1 year while maintaining reliable progress despite interruptions.

Works best with the AWS MCP server but is not required. All AWS interactions in this skill use standard AWS CLI commands that work in any environment with configured AWS credentials.

Critical Rules

Read these before writing any code. Each one is a constraint that will silently break a function if violated.

1. Durable execution must be enabled at function creation time — it cannot be retrofitted. A new Lambda function must be created with durable execution turned on. Migrate the logic into the new function; do not attempt to install the SDK and wrap the handler of the existing function and expect it to work.
2. Durable functions must be invoked with a qualified ARN — a specific version, an alias, or the literal $LATEST suffix. An unqualified function name will fail. See the Invocation Requirements section below for examples.
3. Durable operations cannot be nested. You cannot call context.step(), context.wait(), or context.invoke() from inside another step's callback. Use context.runInChildContext() to group operations instead.
4. All non-deterministic code must run inside steps. Date.now(), Math.random(), UUID generation, API calls, and database queries outside a step will produce different values on replay and corrupt execution state.
5. Closure mutations are lost on replay - return values from steps
6. Side effects outside steps repeat - use context.logger (replay-aware)

When to Load Reference Files

Load the appropriate reference file based on what the user is working on:

• Getting started, basic setup, example, ESLint, or Jest setup -> see getting-started.md
• Understanding replay model, determinism, or non-deterministic errors -> see replay-model-rules.md
• Creating steps, atomic operations, or retry logic -> see step-operations.md
• Waiting, delays, callbacks, external systems, or polling -> see wait-operations.md
• Parallel execution, map operations, batch processing, or concurrency -> see concurrent-operations.md
• Error handling, retry strategies, saga pattern, or compensating transactions -> see error-handling.md
• Advanced error handling, timeout handling, circuit breakers, or conditional retries -> see advanced-error-handling.md
• Testing, local testing, cloud testing, test runner, or flaky tests -> see testing-patterns.md
• Deployment, CloudFormation, CDK, SAM, log groups, deploy, or infrastructure -> see deployment-iac.md
• Advanced patterns, GenAI agents, completion policies, step semantics, or custom serialization -> see advanced-patterns.md
• troubleshooting, stuck execution, failed execution, debug execution ID, execution history, execution error, why did my execution fail, execution timed out, callback not received, diagnose execution, or root cause execution -> see troubleshooting-executions.md