Transaction Watcher

This is a repository to harden your SQL skill, learn Kafka (or Redpanda) and learn Docker.

Your Tasks

This project contains a few tasks for you to work with.

#1 The Watcher

Create a subdirectory called watcher that will do a SQL query periodically to the transactions table, and for every new row on that table, the watcher will produce a message to transactions topic on Redpanda.

The schema of the message is defined on the kafka-schemas directory. Search for transaction.json file.

You must create a Dockerfile for your application. You can choose any language.

You don't need to create a HTTP API for this one. Just create a single function that will run when the program is executed. The application must work without any interference from you. It must work without having anyone (including you) to trigger the run or consume function.

You can see that your watcher is emitting correct message to Redpanda through Redpanda Console that is running on your local machine on port 8080.

There will be environment variable available for you when you run it though Docker Compose:

DATABASE_URL: "postgresql://watcher:password@postgres:5432/watcher?sslmode=disable"
KAFKA_ADDRESSES: "kafka:9092"

#2 The Swimmer

Create a subdirectory called swimmer that will consume the balance topic from Redpanda, and do an event sourcing of a customer's current balance. You must expose a HTTP API that handles a single endpoint of:

GET /current-balance?customer_id=123
Accept: application/json

With a response schema of:

{
  "customer_id": 123,
  "current_balance": 123456
}

It's called swimmer because you will swim through the Redpanda balance topic records, and get an answer from that. I will not give a clue on how you should consume your topic and produce a result based on the customer ID.

For the balance topic schema, you can look for balance.json on kafka-schemas directory.

You must create a Dockerfile for your application. You can choose any language.

Please expose the HTTP API at port 3000.

There will be environment variable available for you when you run it though Docker Compose:

KAFKA_ADDRESSES: "kafka:9092"

#3 The Frontend

This is an optional task.

Create a frontend (on frontend directory) that shows list of customer ID from customer-list service. Then, show the amount or balance that each customer have. You can create a full SPA page, or an SSR website.

You can hit these two endpoints:

GET http://customer-list:7201/customers
Accept: application/json

# Returns list of customer ID
[1,2,3,4,5]

GET http://swimmer:3000/current-balance?customer_id=123
Accept: application/json

# Returns:
{
  "customer_id": 123,
  "current_balance": 123456
}

Hey, the swimmer one is the one you made!

If you are developing it from your local machine, you can replace both customer-list and swimmer hostname into localhost.

You can create a Dockerfile and add a new service schema on docker-compose.yml file to state your frontend container configuration.

How do I know if I did it?

Easy, run the Docker Compose. Build everything. See the frontend if it works. See the Redpanda Console if you published and consume your topics and messages flawlessly.

docker compose up -d

To stop it, use

docker compose down

If you'd like to run just a few services for your local development purposes, for example only postgres and kafka services, you can specify it on the up command, like so:

docker compose up -d postgres kafka

Words of affirmation

Good luck, you can do it!