Building a Production-Ready POS System from Scratch
Building a Production-Ready POS System from Scratch
When I joined BusyParade, the task was clear: build a complete point-of-sale system that could handle real retail operations. Not a prototype. Not an MVP. A production system that handles real money.
The Challenge
Retail POS systems are deceptively complex. On the surface, it's just "scan item, take payment, print receipt." But dig deeper and you find:
- Inventory management across multiple locations
- Complex payment workflows (discounts, partial payments, refunds, reversals)
- Role-based access for cashiers, managers, and admins
- Real-time reporting for business decisions
- Offline capability because internet isn't always reliable
Technical Decisions
Database: PostgreSQL
For a system handling financial transactions, ACID compliance isn't optional. I chose PostgreSQL for:
- Strong transactional guarantees
- Excellent support for complex queries
- JSON columns for flexible product attributes
- Robust backup and recovery options
-- Example: Transaction table with proper constraints
CREATE TABLE transactions (
id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
store_id UUID REFERENCES stores(id),
cashier_id UUID REFERENCES users(id),
total DECIMAL(10, 2) NOT NULL,
status VARCHAR(20) DEFAULT 'pending',
created_at TIMESTAMP DEFAULT NOW(),
completed_at TIMESTAMP,
CONSTRAINT valid_total CHECK (total >= 0)
);Backend: Node.js + Express
TypeScript everywhere. The type safety catches errors before they reach production, and the shared types between frontend and backend reduce integration bugs.
Real-Time Updates
Redis pub/sub for inventory updates across terminals. When one cashier sells the last item, all other terminals know immediately.
Lessons Learned
-
Design for failure - Network will fail, printers will jam, power will go out. Build resilience into every layer.
-
Audit everything - In financial systems, you need to know who did what, when. Every action gets logged.
-
Test with real data - Synthetic test data never captures the edge cases that real products have.
What's Next
The system is live and processing transactions daily. Next up: analytics dashboards and integration with accounting software.
Have questions about building POS systems? Get in touch.