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AWS Lambda Durable Functions

AWSOfficialPublished by AWS

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  • Tool integration
  • Cloud and DevOps
  • Apache-2.0
  • Low risk
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From the author

Builds resilient, long-running, multi-step applications with AWS Lambda durable functions with automatic state persistence, retry logic, and orchestration for long-running executions. Covers the critical replay model, step operations, wait/callback patterns, error handling with saga pattern, testing with LocalDurableTestRunner. Triggers on phrases like lambda durable functions, durable execution, workflow orchestration, state machines, retry/checkpoint patterns, long-running stateful Lambda functions, saga pattern, human-in-the-loop callbacks, reliable serverless applications, context.step, context.wait, context.invoke, context.runInChildContext, withDurableExecution, DurableContext, UnrecoverableInvocationError, durable-execution-sdk, qualified ARN invocation, and durable handler replay.
— the description by AWS

AutoGineer summary

Written by AutoGineer from the skill’s own files, not by the author

This skill provides guidance and patterns for implementing durable, multi-step applications on AWS Lambda. It focuses on the replay model, which allows functions to maintain state across long-running executions—up to one year—by automatically checkpointing progress. The skill covers essential architectural patterns such as the saga pattern for error handling, wait/callback mechanisms for external system integration, and testing strategies using the local test runner. It emphasizes strict adherence to deterministic coding practices required by the replay model to ensure reliable execution.

What it does

  • Enables state persistence for long-running Lambda functions.
  • Provides patterns for implementing the saga pattern and compensating transactions.
  • Supports wait/callback patterns for integrating with external systems.
  • Offers guidance on testing durable functions locally and in the cloud.
  • Defines rules for deterministic code to prevent state corruption during replays.
  • Outlines requirements for qualified ARN invocation and IAM permissions.

When to use it

  • When building workflows that require execution times longer than standard Lambda timeouts.
  • When orchestrating multi-step processes that need to maintain state across interruptions.
  • When implementing reliable, fault-tolerant serverless integrations.
  • When managing complex state machines or human-in-the-loop approval processes.
  • When you need automatic retry logic and checkpointing for critical business processes.

Advantages

  • Resilient execution that survives infrastructure interruptions.
  • Simplified state management without external databases for simple workflows.
  • Native support for complex orchestration patterns like sagas and parallel execution.
  • Built-in replay-aware logging and error handling.
  • Local testing capabilities to validate complex workflow logic.

Usage examples

“How do I implement a multi-step workflow with a wait period in AWS Lambda?”
The agent provides a code example using context.step for logic and context.wait for the delay, ensuring the execution state is persisted correctly.
“Why is my durable function failing during replay?”
The agent helps diagnose non-deterministic code (like Date.now() or Math.random()) placed outside of steps, which causes state corruption.
“How do I handle errors in a long-running durable function?”
The agent explains the saga pattern and how to implement compensating transactions within steps to roll back state if a step fails.
“What are the requirements for invoking a durable Lambda function?”
The agent clarifies that durable functions must be invoked using a qualified ARN (version, alias, or $LATEST) and provides the corresponding AWS CLI command.

Install

  1. Download the skill as a ZIP:

    https://mp-staging.autogineer.com/agent-skills/aws/aws-lambda-durable-functions/download

  2. Unzip it into the cross-client skills folder of your project:

    mkdir -p .agents/skills && unzip aws-lambda-durable-functions.zip -d .agents/skills

Documentation by AWS

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

Quick Reference

Basic Handler Pattern

TypeScript:

import { withDurableExecution, DurableContext } from '@aws/durable-execution-sdk-js';

export const handler = withDurableExecution(async (event, context: DurableContext) => {
  const result = await context.step('process', async () => processData(event));
  return result;
});

Python:

from aws_durable_execution_sdk_python import durable_execution, DurableContext

@durable_execution
def handler(event: dict, context: DurableContext) -> dict:
    result = context.step(lambda _: process_data(event), name='process')
    return result
Python API Differences

The Python SDK differs from TypeScript in several key areas:

  • Steps: Use @durable_step decorator + context.step(my_step(args)), or inline context.step(lambda _: ..., name='...'). Prefer the decorator for automatic step naming.

  • Wait: context.wait(duration=Duration.from_seconds(n), name='...')

  • Exceptions: ExecutionError (permanent), InvocationError (transient), CallbackError (callback failures)

  • Testing: Use DurableFunctionTestRunner class directly - instantiate with handler, use context manager, call run(input=...)

Invocation Requirements

Durable functions require qualified ARNs (version, alias, or $LATEST):

# Valid
aws lambda invoke --function-name my-function:1 output.json
aws lambda invoke --function-name my-function:live output.json

# Invalid - will fail
aws lambda invoke --function-name my-function output.json

IAM Permissions

Your Lambda execution role MUST have the AWSLambdaBasicDurableExecutionRolePolicy managed policy attached. This includes:

  • lambda:CheckpointDurableExecution - Persist execution state

  • lambda:GetDurableExecutionState - Retrieve execution state

  • CloudWatch Logs permissions

Additional permissions needed for:

  • Durable invokes: lambda:InvokeFunction on target function ARNs

  • External callbacks: Systems need lambda:SendDurableExecutionCallbackSuccess and lambda:SendDurableExecutionCallbackFailure

Validation Guidelines

When writing or reviewing durable function code, ALWAYS check for these replay model violations:

  1. Non-deterministic code outside steps: Date.now(), Math.random(), UUID generation, API calls, database queries must all be inside steps

  2. Nested durable operations in step functions: Cannot call context.step(), context.wait(), or context.invoke() inside a step function — use context.runInChildContext() instead

  3. Closure mutations that won't persist: Variables mutated inside steps are NOT preserved across replays — return values from steps instead

  4. Side effects outside steps that repeat on replay: Use context.logger for logging (it is replay-aware and deduplicates automatically)

When implementing or modifying tests for durable functions, ALWAYS verify:

  1. All operations have descriptive names

  2. Tests get operations by NAME, never by index

  3. Replay behavior is tested with multiple invocations

  4. Use LocalDurableTestRunner for local testing

Security Considerations

  • Checkpoint data encryption: Execution state is persisted automatically. Enable KMS encryption on associated CloudWatch Log Groups to protect checkpointed data at rest.

  • Sensitive data in step results: Step return values are checkpointed and persisted. Do not return secrets, raw credentials, or PII from steps — store sensitive data in Secrets Manager or SSM Parameter Store and return references instead.

  • Input validation: Validate and sanitize event payloads at the handler entry point before passing data to steps.

  • Credential management: Retrieve secrets from AWS Secrets Manager or SSM Parameter Store within steps.

  • Callback payload validation: Data received via waitForCallback originates from external systems — validate and sanitize before processing.

  • Logging: Avoid DEBUG log level in non-development environments as it may expose step results and execution state. Enable CloudWatch Logs encryption with KMS.

Resources

Files

references/step-operations.md

Step Operations

Steps are atomic operations with automatic retry and state persistence.

Basic Step Patterns

Python: Two Ways to Define Steps

Recommended: @durable_step Decorator

from aws_durable_execution_sdk_python import durable_step, StepContext

@durable_step
def fetch_user(step_ctx: StepContext, user_id: str):
    """Fetch user from database - reusable step function."""
    return fetch_user_from_api(user_id)

# Call it - name is automatically inferred from function name
result = context.step(fetch_user(user_id))

Alternative: Inline Lambda

# For simple one-off operations
result = context.step(
    func=lambda step_ctx: fetch_user_from_api(user_id),
    name='fetch-user'
)

Use @durable_step for:

  • Reusable step functions

  • Complex logic

  • Better readability and testing

Use lambda for:

  • Simple inline operations

  • One-off transformations

TypeScript: Named Steps

TypeScript:

const result = await context.step('fetch-user', async () => {
  return await fetchUserFromAPI(userId);
});

Best Practice: Always name steps for easier debugging and testing.

Retry Configuration

Exponential Backoff

TypeScript:

import { createRetryStrategy, JitterStrategy } from '@aws/durable-execution-sdk-js';

const result = await context.step(
  'api-call',
  async () => callExternalAPI(),
  {
    retryStrategy: createRetryStrategy({
      maxAttempts: 5,
      initialDelay: { seconds: 1 },
      maxDelay: { seconds: 60 },
      backoffRate: 2.0,
      jitter: JitterStrategy.FULL
    })
  }
);

Python:

# Note: api_call is decorated with @durable_step
from aws_durable_execution_sdk_python.config import StepConfig, Duration
from aws_durable_execution_sdk_python.retries import RetryStrategyConfig, create_retry_strategy, JitterStrategy

retry_config = RetryStrategyConfig(
    max_attempts=5,
    initial_delay=Duration.from_seconds(5),
    max_delay=Duration.from_seconds(60),
    backoff_rate=2.0,
    jitter_strategy=JitterStrategy.FULL
)

result = context.step(
    func=api_call(),
    config=StepConfig(retry_strategy=create_retry_strategy(retry_config))
)
Custom Retry Strategy

TypeScript:

const result = await context.step(
  'custom-retry',
  async () => riskyOperation(),
  {
    retryStrategy: (error, attemptCount) => {
      // Don't retry validation errors
      if (error.name === 'ValidationError') {
        return { shouldRetry: false };
      }
      
      // Retry up to 3 times with exponential backoff
      if (attemptCount < 3) {
        return {
          shouldRetry: true,
          delay: { seconds: Math.pow(2, attemptCount) }
        };
      }
      
      return { shouldRetry: false };
    }
  }
);

Python:

from aws_durable_execution_sdk_python.retries import RetryDecision

def custom_retry(error: Exception, attempt: int) -> RetryDecision:
    if isinstance(error, ValidationError):
        return RetryDecision.no_retry()
    
    if attempt < 3:
        return RetryDecision(
            should_retry=True,
            delay=Duration.from_seconds(2 ** attempt)
        )
    
    return RetryDecision.no_retry()

result = context.step(
    risky_operation(),
    config=StepConfig(retry_strategy=custom_retry)
)
Retryable Error Types

TypeScript:

class NetworkError extends Error {
  name = 'NetworkError';
}

class TimeoutError extends Error {
  name = 'TimeoutError';
}

const result = await context.step(
  'selective-retry',
  async () => operation(),
  {
    retryStrategy: createRetryStrategy({
      maxAttempts: 3,
      retryableErrorTypes: [NetworkError, TimeoutError]
    })
  }
);

Python:

retry_config = RetryStrategyConfig(
    max_attempts=3,
    retryable_error_types=[NetworkError, TimeoutError]
)

Step Semantics

AtLeastOncePerRetry (default)

Step executes at least once on each retry attempt. If the step succeeds but the checkpoint fails (e.g. due to a sandbox crash), the step will re-execute on replay. Use for idempotent operations that can tolerate duplicate execution.

TypeScript:

import { StepSemantics } from '@aws/durable-execution-sdk-js';

const result = await context.step(
  'idempotent-operation',
  async () => idempotentAPI(),
  { semantics: StepSemantics.AtLeastOncePerRetry }
);
AtMostOncePerRetry

Step executes at most once per retry attempt. If a crash happens between the pre-step checkpoint and step completion, the step is skipped on replay rather than re-executed. The step can still run across multiple retry attempts. To guarantee at-most-once overall, pair with retryStrategy: () => ({ shouldRetry: false }).

TypeScript:

import { StepSemantics } from '@aws/durable-execution-sdk-js';

const result = await context.step(
  'charge-payment',
  async () => chargeCard(amount),
  {
    semantics: StepSemantics.AtMostOncePerRetry,
    retryStrategy: () => ({ shouldRetry: false })
  }
);

Python:

from aws_durable_execution_sdk_python.config import StepSemantics, StepConfig

result = context.step(
    charge_card(amount),
    config=StepConfig(
        step_semantics=StepSemantics.AT_MOST_ONCE_PER_RETRY,
        retry_strategy=lambda error, attempt: RetryDecision.no_retry()
    )
)

Custom Serialization

For complex types, provide custom serialization:

TypeScript:

import { createClassSerdesWithDates } from '@aws/durable-execution-sdk-js';

class User {
  id: string = '';
  name: string = '';
  createdAt: Date = new Date();
}

const userSerdes = createClassSerdesWithDates(User, ['createdAt']);

const user = await context.step(
  'fetch-user',
  async () => {
    const user = new User();
    user.id = '123';
    user.name = 'Alice';
    user.createdAt = new Date();
    return user;
  },
  { serdes: userSerdes }
);

Python:

from dataclasses import dataclass
from datetime import datetime

@dataclass
class User:
    id: str
    name: str
    created_at: datetime

# Python SDK handles dataclass serialization automatically
user = context.step(
    lambda _: User('123', 'Alice', datetime.now()),
    name='fetch-user'
)

When to Use Steps vs Child Contexts

Use Steps For:

  • Single atomic operations

  • API calls

  • Database queries

  • Data transformations

  • Operations that should retry as a unit

Use Child Contexts For:

  • Grouping multiple durable operations

  • Complex workflows with steps, waits, and invokes

  • Isolating state tracking

  • Organizing related operations

Example:

// ❌ WRONG: Cannot nest durable operations in step
await context.step('process', async () => {
  await context.wait({ seconds: 1 });  // ERROR!
});

// ✅ CORRECT: Use child context
await context.runInChildContext('process', async (childCtx) => {
  const data = await childCtx.step('fetch', async () => fetch());
  await childCtx.wait({ seconds: 1 });
  return await childCtx.step('save', async () => save(data));
});

Error Handling

Steps throw errors after all retry attempts are exhausted:

TypeScript:

try {
  const result = await context.step('risky', async () => riskyOperation());
} catch (error) {
  if (error instanceof StepError) {
    context.logger.error('Step failed', error.cause);
    // Handle or rethrow
  }
}

Python:

try:
    # Note: risky_operation is decorated with @durable_step
    result = context.step(risky_operation())
except Exception as error:
    context.logger.error('Step failed: %s', str(error))
    # Handle or rethrow

For SDK-specific exceptions, use the base class or specific types:

from aws_durable_execution_sdk_python import DurableExecutionsError

try:
    result = context.step(risky_operation())
except DurableExecutionsError as error:
    context.logger.error('SDK error: %s', str(error))
except Exception as error:
    context.logger.error('Application error: %s', str(error))

Best Practices

  1. Always name steps for debugging and testing

  2. Keep steps atomic - one logical operation per step

  3. Make steps idempotent when possible

  4. Use appropriate retry strategies based on operation type

  5. Handle errors explicitly - don't let them propagate unexpectedly

  6. Use custom serialization for complex types

  7. Choose correct semantics (AtLeastOncePerRetry vs AtMostOncePerRetry)

Requirements and compatibility

Works with: Claude Code, Claude apps, OpenAI Codex, GitHub Copilot, Cursor, Gemini CLI, Kiro, OpenCode, Goose, Amp, Roo Code, JetBrains Junie, Factory Droid, Devin (ex-Windsurf), Mistral Vibe, OpenHands, Letta

“Works with” means the tool reads the open Agent Skills format; a skill written for one tool may use features others lack.

Needs: Needs an MCP server, Needs a command-line tool, Needs Python

Security

What our scanner noticed· Low risk

  • Instructions that use the network

A static scan is not a guarantee. Skills are third-party content: review a skill before you let an agent use it.

Attribution and licence

Published by
AWS
Publisher
AWS (Official)
Source
aws/agent-toolkit-for-aws · skills/specialized-skills/serverless-skills/aws-lambda-durable-functions · commit 0a218f8
Licence
Apache License 2.0 (redistribution allowed)
  • LICENSE (added by AutoGineer from LICENSE)
  • NOTICE (added by AutoGineer from NOTICE)
  • ATTRIBUTION.md (written by AutoGineer)
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