# A 5-year-old fintech hand-rolled every layer: custom Python extracts, a custom S3 layout, Postgres-a

Canonical URL: <https://datadriven.io/problems/a-5-year-old-fintech-hand-rolled-every-layer-custom-python-e81d8e75>

Domain: Pipeline Design · Difficulty: medium

## Problem

A 5-year-old fintech hand-rolled every layer: custom Python extracts, a custom S3 layout, Postgres-as-warehouse, a cron-script 'orchestrator', an in-house catalog, and Slack-script 'observability'. One full-time engineer maintains each layer, and the proprietary attribution model is mixed into the same custom mess. Apply the section's build-vs-buy rule: keep custom only for the differentiated business logic, replace every commodity layer with a managed vendor.

## Related

- [All practice problems](https://datadriven.io/problems)
- [Mock interview mode](https://datadriven.io/interview/a-5-year-old-fintech-hand-rolled-every-layer-custom-python-e81d8e75)
- [System Design Interview Questions](https://datadriven.io/data-engineering-system-design)
- [Data Engineering Interview Prep Guide](https://datadriven.io/data-engineer-interview-prep)
- [Daily Challenge](https://datadriven.io/daily)

---

Source: DataDriven (https://datadriven.io). 100% free data engineering interview prep. Live code execution against Postgres 16, Python 3.11, and Spark sandboxes. No paywall, no premium tier, no signup gate.