Building a Bank POC — Secure Foundations
I started this project a few days ago as a personal challenge: I wanted a focused, production-minded playground where I could sharpen systems design, reliability, and backend craftsmanship. The idea was simple — build a Bank Proof-of-Concept (Bank POC) that behaves like a real banking core: secure, observable, and transaction-safe.
This post is intentionally short — the repo is early-stage. Right now the README is written and JWT-based user authentication is implemented. No flashy UI yet; the point is to demonstrate how the backend should work and to level up my engineering skills.
⚙️ High-Level Architecture (The Fortress Blueprint)
+---------+ HTTPS +------------+ SQL +-----------+
| Client | <-----------> | Spring API | <---------> | PostgreSQL|
+---------+ +-----+------+ +-----------+
|
Redis <----+----> Kafka (optional)
| ^
(cache, OTP, locks, |
sessions, streams) |
|
Metrics/Logs/Traces
/ | \
Prometheus Grafana ELK/Logstash
💡 Why I picked this project
- Leveling up: working through concurrency, idempotency, observability, and resilience is the fastest practical way I know to get better at backend engineering.
- Real-world constraints: unlike toy apps, financial systems force you to think about atomicity, auditability, and failure modes.
- Portfolio & storytelling: this project is both a learning log and a portfolio piece I can point to during interviews.
⚙️ What’s implemented (so far)
- README: clear architecture overview, core user flows, and run instructions.
- JWT Authentication: secure, stateless authentication using Spring Security. This includes token issuance and the basic auth flow for users to sign in.
That’s it for code features so far — everything else is planning, architecture notes, and infra scaffolding. I started small on purpose: get auth right, then build the account/transfer flows the correct way.
🧱 Core principles I’m following
- Database as source of truth — balances live in Postgres, not Redis.
- Atomic transfers — debit and credit happen inside a single DB transaction.
- Idempotency — all transfer endpoints will accept an idempotency key to prevent double spending.
- Auditability — immutable audit logs for every money-moving action.
- Observability-first — metrics, traces, and structured logs from day one.
🧩 Example user flow (planned)
- Register → user gets
kyc_status = PENDING, account createdINACTIVE. - Admin KYC approve → user and account become
ACTIVE. - Set PIN → user sets card transaction PIN (hashed & stored).
- Login → JWT issued; device trust and OTP flows may be used for untrusted devices.
- Transfer → user submits transfer with
idempotencyKeyandpin→ server validates, locks accounts, executes atomic transfer.
🧭 Next immediate steps
I’ll be iterating in short cycles. Next work items (in approximate order):
- Account creation + balances (with safe locking patterns)
- Transfer endpoint with idempotency (SELECT FOR UPDATE; audit logs)
- Add Redis distributed locks for cross-instance safety
- Add Prometheus metrics & Jaeger spans for transfer flows
- Write integration tests (DB + transaction scenarios)
I’ll publish follow-up posts as features land.
🎯 Why this is a good showcase
Even in early stages, this project shows:
- Thoughtful architecture choices
- Real security baseline (JWT auth)
- Focus on reliability and observability
- A plan to incrementally add production-grade features
That’s exactly the sort of work I want to talk about with engineering teams and interviewers.
🧩 Repo
https://github.com/NeurologiaLogic/bankpoc-secure-transfer-system
# Clone
git clone https://github.com/NeurologiaLogic/bankpoc-secure-transfer-system.git
cd bankpoc-secure-transfer-system
# Start infra (Postgres, Redis, Prometheus, Grafana, Jaeger)
docker compose up -d
# Run the app (from project root)
./mvnw spring-boot:run