foorocks

Foo really rocks. Example of using zio-http, zio-kafka, zio-schema, zio-rocksdb, zio-streams and a bunch of Scala libraries (especially zio ecosystem) to create an event sourcing application.

Entities

There are two entities: Stock and Movement. There are a few fixed stocks like amzn (Amazon), nflx (Netflix) and glts (Glints).

case class Stock(
    id: UUID = UUID.randomUUID(),
    symbol: String,
    price: BigDecimal = 0
);

Movements are changes in price to the stock.

case class Movement(
    stockId: UUID,
    change: BigDecimal = 0
);

So a movement with stockId for nflx with change=10 ie Movement("nflx-uuid", 10), is an event which when consumed, changes the nflx stock by +10 ie nflxStock.price = nflxStock.price + 10.

The goal is to create an application that can receive these movements at high frequencies and update the stock correctly with low latency and good throughput.

External Components

Kafka

Kafka is the event bus (or a distributed commit log) that receives, stores and shares Movement data for stocks. It is also/will be used for changelog data to the Stock so when our application goes down and comes back up, we start where we left off.

RocksDB

Technically not externally but more so embedded; This is the store we use to read and write stateful Stock data. Changes to Stock after consuming Movement will be persisted via this db. RocksDB is used for persistence and because it is embedded, it is fast. Not to mention the configurable block cache and the memtables.

Internal Components

Simulator/Movement Producer

This is a Kafka producer that generates random Movement data and produces it to Kafka.

Consumer

Consumes Movement produced by the Simulator and changes the stock price, storing it in RocksDB (and change logging into Kafka in the future)

Web API/App

zio-http application that is used to retrieve the stock data by id from the state store.

Setup

Requirements

1. docker
2. docker-compose
3. Java (preferably Java 17). If you are using M1 Mac, use SDKMAN and java 17.0.5-zulu
4. sbt

Setup External Components

docker-compose up -d broker

Run application

sbt run