README

aws-event-stream

**This library is based on https://github.com/thiagobustamante/node-eventstore

It is an open source library to create Event Stores that works with AWS using DynamoDB as Provider and SNS to publish messages.

Motivation

This is an open source library to create Event Stores that works with DynamoDB as persistence providers and SNS notification systems.

The Event Store is a database accompanied by a publication and subscription system. The database stores all the events related to an event stream. The pub / sub system allows other systems or microservices to react to changes in event streams. It is a core component in any event sourcing + CQRS architectures.

Installing

npm install --save aws-event-stream

Usage

Create EventStore

To Create an EventStore you must provide two implementations:

A DynamoDBProvider: Responsible for events persistence in the store.
A SNSPublisher (Optional): Responsible for notify any process interested in modifications on the store streams.

If there is no publisher provided, the event store will not send any notification.

const awsConfig = { region: 'us-east-1' };

const dynamodbConfig = {
    awsConfig: awsConfig,
    dynamodb: {
        tableName: 'events'
    }
} as Config;

const eventStore = new EventStore(
    new DynamodbProvider(dynamodbConfig),
    new SNSPublisher('arn:sns', awsConfig),
);

DynamodbConfig

The object DynamodbConfig is related to Dynamodb configuration, the possible parameters are:

| Parameter | Description |

Parameter	Description
tableName	The name of the table.
createTable	True: create the table, False assume that table alreaday exists.
readCapacityUnit	The total number of read capacity units consumed by the operation.
writeCapacityUnit	The total number of write capacity units consumed by the operation.
endpointUrl	An Endpoint object representing the endpoint URL for service requests.
maxRetries	The maximum amount of retries to attempt with a request.
httpOptions	A set of options to pass to the low-level HTTP request.
ttl	Time to Live (TTL) in seconds on the specified table.

Adding Events

To add Events you need to ask to EventStore a reference to an EventStream. You can add Events passing anything you want as a payload.

const orderStream = eventStore.getEventStream('orders', '123');
await orderStream.addEvent({ data: 'any data', eventType: 'PLACED' });

Reading Events

To read Events you need to ask to EventStore a reference to an EventStream. You can read a stream to receive an ordered list containing all the events in the store.

getEvents()

Returns an array with all events published in the Stream specified.

const orderStream = eventStore.getEventStream('orders', '123');
const events = await orderStream.getEvents();

Example of event from getEvents method:

[
    { 
        'commitTimestamp': 1611206813, 
        'eventType': 'SENT', 
        'payload': {'text': 'EVENT PAYLOAD', 'sequence': 1 }
    },
    { 
        'commitTimestamp': 1611206823, 
        'eventType': 'PLACED', 
        'payload': {'text': 'EVENT PAYLOAD', 'sequence': 2 }
    }
]

Returns an Object with all data from events happened in a Stream. What happens is a merge in all fields from all events, keeping the eventTypes as an array.

The fields which have conflicts will always be considered the last event.

const orderStream = eventStore.getEventStream('orders', '123');
await orderStream.loadFromHistory();

Example of event from loadFromHistory method:

    { 
        'commitTimestamp': 1611206823, 
        'eventTypes': ['SENT', 'PLACED'], 
        'payload': {'text': "EVENT PAYLOAD", 'eventType': 'PLACED'}, 'sequence': 2 
    }

Integration Test

Steps:

TMPDIR=/private$TMPDIR docker-compose up
npm run test:integration:jest
aws dynamodb --endpoint-url=http://localhost:4566 scan --table-name events-now
aws sns --endpoint-url=http://localhost:4566 list-topics

Usage no npm install needed!