EventBridge Message Bus Adapter

DRY Castore MessageBus definition using AWS EventBridge and AWS S3.

This adapter works like the EventBridge Message Bus Adapter (it actually uses it under the hood), excepts that entry sizes are checked before publishing messages to EventBridge. If they are over the 256KB limit, they are written on a s3 bucket instead, and a message is sent containing a pre-signed URL, as recommended by AWS.

Do not forget to set a lifecycle configuration on your s3 bucket to delete the written objects after the presigned URL has expired to avoid high s3 bills! 🤑

📥 Installation

# npm
npm install @castore/event-bridge-s3-message-bus-adapter

# yarn
yarn add @castore/event-bridge-s3-message-bus-adapter

This package has @castore/core, @aws-sdk/client-eventbridge (above v3), @aws-sdk/client-eventbridge (above v3) and @aws-sdk/s3-request-presigner (above v3) as peer dependencies, so you will have to install them as well:

# npm
npm install @castore/core @aws-sdk/client-eventbridge @aws-sdk/client-s3 @aws-sdk/s3-request-presigner

# yarn
yarn add @castore/core @aws-sdk/client-eventbridge @aws-sdk/client-s3 @aws-sdk/s3-request-presigner

👩‍💻 Usage

import { EventBridgeClient } from '@aws-sdk/client-eventbridge';
import { S3Client } from '@aws-sdk/client-s3';

import { EventBridgeS3MessageBusAdapter } from '@castore/event-bridge-s3-message-bus-adapter';

const eventBridgeClient = new EventBridgeClient({});
const s3Client = new S3Client({});

const messageBusAdapter = new EventBridgeS3MessageBusAdapter({
  eventBusName: 'my-event-bus-name',
  eventBridgeClient,
  s3BucketName: 'my-bucket-name',
  s3Client,
  // 👇 Optional s3 prefix for temporary data
  s3Prefix: 'temporary-storage/',
  // 👇 Optional s3 presignature expiration in seconds (defaults to 900)
  s3PreSignatureExpirationInSec: 3600
});

// 👇 Alternatively, provide a getter
const messageBusAdapter = new EventBridgeS3MessageBusAdapter({
  eventBusName: () => process.env.MY_EVENT_BUS_NAME,
  s3BucketName: () => process.env.MY_BUCKET_NAME
  ...
});

const appMessageBus = new NotificationMessageBus({
  ...
  messageBusAdapter
})

This will directly plug your MessageBus to EventBridge and S3 🙌

🤔 How it works

You can read the EventBridge Message Bus Adapter documentation for regular cases.

When an entry is oversized, its Detail is saved as a JSON object in the provided s3 bucket. It's key is a concatenation of the constructor s3Prefix option, the eventStoreId and aggregateId of the event and the current timestamp:

const key = 'temporary-storage/POKEMONS/pikachu1/2020-01-01T00:00:00.000Z';

If the event is a notification or state-carrying event, the version is also added to the mix:

// 👇 Date is suffixed by the version
const key = 'temporary-storage/POKEMONS/pikachu1/2020-01-01T00:00:00.000Z#3';

On the listeners side, you can use the EventBridgeS3MessageBusMessage TS type to type your argument, and the parseMessage util to fetch the message if it has been uploaded to S3 (it passes it through otherwise):

import {
  EventBridgeS3MessageBusMessage,
  parseMessage,
} from '@castore/event-bridge-s3-message-bus-adapter';

const listener = async (
  message: EventBridgeS3MessageBusMessage<typeof appMessageBus>,
) => {
  // 🙌 Correctly typed!
  const { eventStoreId, event } = await parseMessage(message);
};

Note that parseMessage uses fetch under the hood, so you will have to provide it if your version of node doesn't:

import fetch from 'node-fetch';

import {
  EventBridgeS3MessageBusMessage,
  parseMessage,
} from '@castore/event-bridge-s3-message-bus-adapter';

const listener = async (
  message: EventBridgeS3MessageBusMessage<typeof appMessageBus>,
) => {
  const { eventStoreId, event } = await parseMessage(message, { fetch });
};

You can provide event store ids and event types if you listener only listens to specific event types:

import type { EventBridgeS3MessageBusMessage } from '@castore/event-bridge-s3-message-bus-adapter';

const listener = async (
  message: EventBridgeS3MessageBusMessage<
    typeof appMessageBus,
    'POKEMONS', // <= Only listen to the 'POKEMONS' event store events (optional)
    'POKEMON_APPEARED' // <= Only listen to 'POKEMON_APPEARED' events (optional)
  >,
) => {
  // 🙌 Correctly typed!
  const { eventStoreId, event } = await parseMessage(message);
};

🔑 IAM

The publishMessage method requires the events:PutEvents IAM permission on the provided event bus, as well as the s3:putObject and s3:getObject IAM permissions on the provided s3 bucket at the desired keys (e.g. my-bucket-name/temporary-storage/*).

The parseMessage doesn't require any permission as the messageURL is pre-signed.