Challenge

Rinha de Backend 2024/Q1

The Rinha de Backend is a Brazilian backend programming challenge. The 2024/Q1 edition simulates a fictional bank called “Rinha Financeira” that manages up to 5 named clients, each seeded at startup with a credit limit and initial balance.

The interesting part is not the endpoint count; it is the combination of high write contention, strict response semantics, and a shared container budget small enough to punish waste.

Endpoint Contract

Endpoint	Method	Success	Validation / rejection
`/clientes/{id}/transacoes`	`POST`	`200` with `limite` and updated `saldo`	`400` for a missing JSON payload, `404` for unknown client, `422` for invalid transaction fields or exceeded limit
`/clientes/{id}/extrato`	`GET`	`200` with `saldo` and recent transactions	`404` for unknown client
`/healthz`	`GET`	`200` with `Healthy`	Used by container and CI smoke checks

Transaction payload

{
  "valor": 1000,
  "tipo": "c",
  "descricao": "deposito"
}

Runtime validation in src/WebApi/app.py keeps the contract narrow:

valor must be a positive integer value.
tipo must be c for credit or d for debit.
descricao must be a non-empty string with at most 10 characters.
Client IDs are fixed to 1 through 5.

The runtime client table is intentionally static and mirrors the seed data in docker-entrypoint-initdb.d/rinha.dump.sql:

Client ID	Credit limit	Initial balance
`1`	`100000`	`0`
`2`	`80000`	`0`
`3`	`1000000`	`0`
`4`	`10000000`	`0`
`5`	`500000`	`0`

Consistency Requirement

Debit requests must never push a client past their configured credit limit. This implementation keeps that invariant in the database by calling InsertTransacao() for the balance update and limit check in one atomic operation.

Constraints

The challenge imposes strict resource limits across all containers combined:

Resource	Total budget	Where it goes in this repo
CPU	`1.5`	API instances, PostgreSQL, and NGINX
Memory	`550MB`	API instances, PostgreSQL, and NGINX
Load	k6 stress script	Concurrent transactions and statement requests

The observability sidecars and k6 runner are useful during local experiments, but the challenge budget centers on the application stack under test.

Source

Full specification: github.com/zanfranceschi/rinha-de-backend-2024-q1