Changelog

February 24, 2026 · View on GitHub

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog.

[1.0.0] - 2026-02-23

Rewritten in TypeScript with a feature flag configuration model.

Added

  • TypeScript rewrite with full type definitions
  • Feature flag configuration model — each failure mode is an independent flag with its own percentage; multiple can be active simultaneously
  • timeout and corruption failure modes
  • Event-based targeting via match conditions (eq, exists, startsWith, regex)
  • Native AppConfig Feature Flags support with auto-disabled library cache
  • Middy middleware via failure-lambda/middy subpath export
  • Configuration validation with structured JSON logging (ReDoS detection, range clamping, fail-closed on invalid flags)
  • CLI tool (npx failure-lambda) for managing configuration with saved profiles, SSM and AppConfig backends
  • Lambda Layer (x86_64, arm64) with Rust proxy for zero-code fault injection across any managed runtime — includes LD_PRELOAD DNS denylist interception

Changed

  • AWS SDK v3, native fetch(), dns.lookup monkey-patching (replaces aws-sdk v2, node-fetch, mitm)
  • Dual CJS/ESM package output; minimum Node.js 20
  • Examples updated to Node.js 22, SDK v3; SAM example includes wrapper and Middy variants

Removed

  • node-fetch and mitm dependencies
  • Support for Node.js < 20
  • Flat {isEnabled, failureMode, ...} configuration format (0.x)

[0.4.4] - 2022-02-14

Changed

  • Switch to node-fetch@2

[0.4.3] - 2022-02-14

Added

  • MIT license file
  • New sample applications for SAM, CDK, and Serverless Framework

Changed

  • Updated dependencies

[0.4.2] - 2021-03-16

Fixed

  • Fixed mitm listener state management to prevent traffic leaking through during enable/disable
  • Fixed mitm not disabling when no longer needed
  • Moved mitm object to library global namespace so that it persists across function invocations

Changed

  • Syntax formatting

[0.4.1] - 2020-10-26

Added

  • Made AppConfig Lambda extension port configurable using environment variable

[0.4.0] - 2020-10-25

Added

  • Optional support for AWS AppConfig, allowing to validate failure configuration, deploy configuration using gradual or non-gradual deploy strategy, monitor deployed configuration with automatic rollback if CloudWatch Alarms is configured, and caching of configuration
  • Hardcoded default configuration with isEnabled: false, to use if issues loading configuration from Parameter Store or AppConfig

[0.3.1] - 2020-10-21

Fixed

  • Change mitm mode back to connect to fix issue with all connections being blocked

[0.3.0] - 2020-08-24

Changed

  • Changed mitm mode from connect to connection for quicker enable/disable of failure injection
  • Renamed block list failure injection to denylist (breaking change for that failure mode)
  • Updated dependencies

[0.2.0] - 2020-02-17

Added

  • Block list failure
  • Updated example application to store file in S3 and item in DynamoDB

[0.1.1] - 2020-02-13

Fixed

  • Fixed issue with exception injection not throwing the exception

[0.1.0] - 2019-12-30

Added

  • Disk space failure
  • Updated example application to store example file in tmp

[0.0.1] - 2019-12-23

Added

  • Initial release