@aws-lambda-powertools/idempotency NPM

Powertools for AWS Lambda (TypeScript) - Idempotency Utility

Powertools for AWS Lambda (TypeScript) is a developer toolkit to implement Serverless best practices and increase developer velocity.

You can use the package in both TypeScript and JavaScript code bases.

Intro

This package provides a utility to implement idempotency in your Lambda functions. You can either use it to wrap a function, decorate a method, or as Middy middleware to make your AWS Lambda handler idempotent.

The current implementation provides a persistence layer for Amazon DynamoDB, which offers a variety of configuration options. You can also bring your own persistence layer by extending the BasePersistenceLayer class.

Key features

Prevent Lambda handler from executing more than once on the same event payload during a time window
Ensure Lambda handler returns the same result when called with the same payload
Select a subset of the event as the idempotency key using JMESPath expressions
Set a time window in which records with the same payload should be considered duplicates
Expires in-progress executions if the Lambda function times out halfway through

Usage

To get started, install the library by running:

npm i @aws-lambda-powertools/idempotency @aws-sdk/client-dynamodb @aws-sdk/lib-dynamodb

Next, review the IAM permissions attached to your AWS Lambda function and make sure you allow the actions detailed in the documentation of the utility.

Function wrapper

You can make any function idempotent, and safe to retry, by wrapping it using the makeIdempotent higher-order function.

The function wrapper takes a reference to the function to be made idempotent as first argument, and an object with options as second argument.

When you wrap your Lambda handler function, the utility uses the content of the event parameter to handle the idempotency logic.

import { makeIdempotent } from '@aws-lambda-powertools/idempotency';
import { DynamoDBPersistenceLayer } from '@aws-lambda-powertools/idempotency/dynamodb';
import type { Context, APIGatewayProxyEvent } from 'aws-lambda';

const persistenceStore = new DynamoDBPersistenceLayer({
  tableName: 'idempotencyTableName',
});

const myHandler = async (
  event: APIGatewayProxyEvent,
  _context: Context
): Promise<void> => {
  // your code goes here here
};

export const handler = makeIdempotent(myHandler, {
  persistenceStore,
});

You can also use the makeIdempotent function to wrap any other arbitrary function, not just Lambda handlers.

import { makeIdempotent } from '@aws-lambda-powertools/idempotency';
import { DynamoDBPersistenceLayer } from '@aws-lambda-powertools/idempotency/dynamodb';
import type { Context, SQSEvent, SQSRecord } from 'aws-lambda';

const persistenceStore = new DynamoDBPersistenceLayer({
  tableName: 'idempotencyTableName',
});

const processingFunction = async (payload: SQSRecord): Promise<void> => {
  // your code goes here here
};

const processIdempotently = makeIdempotent(processingFunction, {
  persistenceStore,
});

export const handler = async (
  event: SQSEvent,
  _context: Context
): Promise<void> => {
  for (const record of event.Records) {
    await processIdempotently(record);
  }
};

If your function has multiple arguments, you can use the dataIndexArgument option to specify which argument should be used as the idempotency key.

import { makeIdempotent } from '@aws-lambda-powertools/idempotency';
import { DynamoDBPersistenceLayer } from '@aws-lambda-powertools/idempotency/dynamodb';
import type { Context, SQSEvent, SQSRecord } from 'aws-lambda';

const persistenceStore = new DynamoDBPersistenceLayer({
  tableName: 'idempotencyTableName',
});

const processingFunction = async (payload: SQSRecord, customerId: string): Promise<void> => {
  // your code goes here here
};

const processIdempotently = makeIdempotent(processingFunction, {
  persistenceStore,
  // this tells the utility to use the second argument (`customerId`) as the idempotency key
  dataIndexArgument: 1, 
});

export const handler = async (
  event: SQSEvent,
  _context: Context
): Promise<void> => {
  for (const record of event.Records) {
    await processIdempotently(record, 'customer-123');
  }
};

Note that you can also specify a JMESPath expression in the Idempotency config object to select a subset of the event payload as the idempotency key. This is useful when dealing with payloads that contain timestamps or request ids.

import { makeIdempotent, IdempotencyConfig } from '@aws-lambda-powertools/idempotency';
import { DynamoDBPersistenceLayer } from '@aws-lambda-powertools/idempotency/dynamodb';
import type { Context, APIGatewayProxyEvent } from 'aws-lambda';

const persistenceStore = new DynamoDBPersistenceLayer({
  tableName: 'idempotencyTableName',
});

const myHandler = async (
  event: APIGatewayProxyEvent,
  _context: Context
): Promise<void> => {
  // your code goes here here
};

export const handler = makeIdempotent(myHandler, {
  persistenceStore,
  config: new IdempotencyConfig({
    eventKeyJmespath: 'requestContext.identity.user',
  }),
});

Additionally, you can also use one of the JMESPath built-in functions like powertools_json() to decode keys and use parts of the payload as the idempotency key.

import { makeIdempotent, IdempotencyConfig } from '@aws-lambda-powertools/idempotency';
import { DynamoDBPersistenceLayer } from '@aws-lambda-powertools/idempotency/dynamodb';
import type { Context, APIGatewayProxyEvent } from 'aws-lambda';

const persistenceStore = new DynamoDBPersistenceLayer({
  tableName: 'idempotencyTableName',
});

const myHandler = async (
  event: APIGatewayProxyEvent,
  _context: Context
): Promise<void> => {
  // your code goes here here
};

export const handler = makeIdempotent(myHandler, {
  persistenceStore,
  config: new IdempotencyConfig({
    eventKeyJmespath: 'powertools_json(body).["user", "productId"]',
  }),
});

Check the docs for more examples.

Decorator

You can make any function idempotent, and safe to retry, by decorating it using the @idempotent decorator.

import { idempotent } from '@aws-lambda-powertools/idempotency';
import { LambdaInterface } from '@aws-lambda-powertools/commons';
import { DynamoDBPersistenceLayer } from '@aws-lambda-powertools/idempotency/dynamodb';
import type { Context, APIGatewayProxyEvent } from 'aws-lambda';

const persistenceStore = new DynamoDBPersistenceLayer({
  tableName: 'idempotencyTableName',
});

class MyHandler extends LambdaInterface {
  @idempotent({ persistenceStore: dynamoDBPersistenceLayer })
  public async handler(
    event: APIGatewayProxyEvent,
    context: Context
  ): Promise<void> {
    // your code goes here here
  }
}

const handlerClass = new MyHandler();
export const handler = handlerClass.handler.bind(handlerClass);

Using the same decorator, you can also make any other arbitrary method idempotent.

import { idempotent } from '@aws-lambda-powertools/idempotency';
import { LambdaInterface } from '@aws-lambda-powertools/commons';
import { DynamoDBPersistenceLayer } from '@aws-lambda-powertools/idempotency/dynamodb';
import type { Context } from 'aws-lambda';

const persistenceStore = new DynamoDBPersistenceLayer({
  tableName: 'idempotencyTableName',
});

class MyHandler extends LambdaInterface {
  
  public async handler(
    event: unknown,
    context: Context
  ): Promise<void> {
    for(const record of event.Records) {
      await this.processIdempotently(record);
    }
  }
  
  @idempotent({ persistenceStore: dynamoDBPersistenceLayer })
  private async process(record: unknown): Promise<void> {
    // process each code idempotently
  }
}

const handlerClass = new MyHandler();
export const handler = handlerClass.handler.bind(handlerClass);

The decorator configuration options are identical with the ones of the makeIdempotent function. Check the docs for more examples.

Middy middleware

If instead you use Middy, you can use the makeHandlerIdempotent middleware. When using the middleware your Lambda handler becomes idempotent.

By default, the Idempotency utility will use the full event payload to create an hash and determine if a request is idempotent, and therefore it should not be retried. When dealing with a more elaborate payload, where parts of the payload always change you should use the IdempotencyConfig object to instruct the utility to only use a portion of your payload. This is useful when dealing with payloads that contain timestamps or request ids.

import { IdempotencyConfig } from '@aws-lambda-powertools/idempotency';
import { makeHandlerIdempotent } from '@aws-lambda-powertools/idempotency/middleware';
import { DynamoDBPersistenceLayer } from '@aws-lambda-powertools/idempotency/dynamodb';
import middy from '@middy/core';
import type { Context, APIGatewayProxyEvent } from 'aws-lambda';

const persistenceStore = new DynamoDBPersistenceLayer({
  tableName: 'idempotencyTableName',
});
const config = new IdempotencyConfig({
  hashFunction: 'md5',
  useLocalCache: false,
  expiresAfterSeconds: 3600,
  throwOnNoIdempotencyKey: false,
  eventKeyJmesPath: 'headers.idempotency-key',
});

export const handler = middy(
  async (_event: APIGatewayProxyEvent, _context: Context): Promise<void> => {
    // your code goes here here
  }
).use(
  makeHandlerIdempotent({
    config,
    persistenceStore,
  })
);

Check the docs for more examples.

DynamoDB persistence layer

You can use a DynamoDB Table to store the idempotency information. This enables you to keep track of the hash key, payload, status for progress, expiration, and much more.

You can customize most of the configuration options of the table, i.e the names of the attributes. See the API documentation for more details.

Contribute

If you are interested in contributing to this project, please refer to our Contributing Guidelines.

Roadmap

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Help us prioritize upcoming functionalities or utilities by upvoting existing RFCs and feature requests, or creating new ones, in this GitHub repository.

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