AWS Serverless Event Sourcing POC

A proof-of-concept for building a event sourcing stuff on top of AWS Serverless platform.

Application consists of a simple API Gateway with three endpoints. One for adding events into event store , one for listing the items from the aggregated read model and one for triggering the replay functionality.

Built with AWS-CDK and Node.js.

Disclaimer

This project is meant for proofing the concept. Use by your own risk. :)

Architecture

Usage

Deployment

Run npm install on app directory
Create an .env file (See section "Environment variables" below)
Define env vars listed below
Run npm run deploy

Environment variables

API_KEY - Required API Key which must be spesified on the request targeting the API Gateway endpoints
TRACING - Optional boolean (true/false) for enabling the AWS X-Ray tracing
STACK_NAME - Optional name override for the stack

Tracing and Debugging

Application is instrumented and will save the traces for debugging into AWS X-Ray if TRACING enviroment variable is defined.
By default, all every lambda function saves the logs into Amazon Cloudwatch

An example test case

"Testing read model" only shows items sent into stream eb724435-02cb-4c68-9d7a-4b6471c5a810, so you should use that as a streamId.
AddEvent does not validate the event context! You should use the event structure below.
Only processed event types are ITEM_CREATED, ITEM_AMOUNT_CHANGED and ITEM_DELETED.
Item id is just an unique string, you can have n+1 items, but event ITEM_CREATED should be called for all of them.

Note IT takes a few seconds change to propagate into read model as event sourcing + CQRS model is eventual consistent.

Below is a simple test case for the understanding the poc on high level:

Send a POST request into /addEvent endpoint with a following payload

{
    "streamId": "eb724435-02cb-4c68-9d7a-4b6471c5a810",
    "type": "ITEM_CREATED",
    "data": {
        "itemId": "1",
        "amount": 225
    }
}

See that item creation was correctly projected into read model by sending a GET request into /listTestItems endpoint
Send a POST request into /addEvent endpoint to update the amount

{
    "streamId": "eb724435-02cb-4c68-9d7a-4b6471c5a810",
    "type": "ITEM_AMOUNT_CHANGED",
    "data": {
        "itemId": "1",
        "amount": 500
    }
}

Read model should now be updated, call /listTestItems again!
Delete item by sending a ITEM_DELETED event into /addEvent endpoint

{
    "streamId": "eb724435-02cb-4c68-9d7a-4b6471c5a810",
    "type": "ITEM_DELETED",
    "data": {
        "itemId": "1"
    }
}

Read model should now be empty, call /listTestItems again!

Quutti/aws-serverless-event-sourcing-poc