Skip to main content
Joel MayJoel May

Offline-First Point of Sale That Keeps Selling Without Internet

FintechReactNode.jsPostgreSQL
Offline-first synchronization for uninterrupted operation

The Challenge

  • Real-time inventory: Instant stock synchronization across multiple POS terminals
  • Offline-first strategy: Full operation without internet, later synchronization
  • Sync conflicts: Conflict resolution when multiple devices modify the same record
  • Transactional consistency: ACID guarantee in sales and inventory operations

Solution Architecture

PWARESTReal-timeWebSocketPOS Terminal (React)Service WorkerIndexedDBAPI Gateway (Node)Redis CachePostgreSQLSocket.IO
System architecture diagram showing nodes and connections

POS Terminal

React application with Service Worker for caching, IndexedDB for local storage of pending transactions

API Gateway

Node.js/Express with Circuit Breaker pattern, transaction validation, processing queue

Cache and Database

PostgreSQL with jsonb extension for metadata, Redis for inventory cache and optimistic locking

Real-Time

Socket.IO for push notifications on inventory changes, automatic reconnection

Results

0%

Transaction loss

<200ms

Average latency

95%

Discrepancy reduction

POS - Offline-First Point of Sale | Joel May