accounts

core banking service

features

• accounts
• add money to account
• transfer money between accounts

considerations

• Disable updates & deletes on transaction_lines table
• Every transaction results in a debit and credit
• We store lowest form of values (cents)
• We perform balance checks before transacting between accounts
• Deposits debit genesis account, whose balance represents total risk
• We assume currency USD with 2 decimal places of precision
• We use transaction references to prevent duplicate transactions (idempotency key)

improvements

• async processing of transactions
• support for multiple currencies
• robust user authn & authz

setup

using docker (easier)

1. In the root of the project, run docker compose up
2. This should boot up a local postgresql instance & an instance of the accounts service.
3. Accounts service should be running on port 8080.

barebones (doable)

1. Ensure you have a postgres db setup with the right dbname, user, password and sslmode.
2. Modify the Makefile in the project root, and set your DB_URL and PORT
3. To run, make run
4. To build make build
5. To test make test

interactions

curl --location 'localhost:8080/users' \
--header 'Content-Type: application/json' \
--data-raw '{
    "email": "[email protected]"
}'

curl --location 'localhost:8080/accounts' \
--header 'Content-Type: application/json' \
--data '{
    "user_id": 5
}'

curl --location 'localhost:8080/transactions' \
--header 'Content-Type: application/json' \
--data '{
    "to": "985270462",
    "type": "deposit",
    "amount": 100,
    "reference": "ok"
}'

curl --location 'localhost:8080/transactions' \
--header 'Content-Type: application/json' \
--data '{
    "from": "810093581",
    "to": "985270462",
    "type": "transfer",
    "amount": 100,
    "reference": "lekkero"
}'

curl --location 'localhost:8080/accounts/715733003'

notes

This is an improvement on cashapp, which I wrote 4 years ago. Code is much cleaner to follow & easier to extend. It also has quite good test coverage.