Your inventory system shows 47 units in stock, but the warehouse just sold the last one to another customer. The dreaded “oversold” email hits your inbox as you explain to an angry client why their order was cancelled. This happens because your REST API polling checks inventory every 30 seconds, and in e-commerce, 30 seconds is an eternity.
In this article, we’ll discuss inventory management software development practices that help you eschew such situations and compare WebSockets and REST APIs.
The Hidden Cost of “Good Enough” Inventory Systems
I’ve seen this disaster play out dozens of times. A client’s fashion e-commerce site would show items available while their warehouse management system had already allocated the last units to other orders. The culprit is their REST API polling every 15 seconds, thinking that was “fast enough.”
The brutal performance reality:
- WebSocket enhances monitoring stats by 98.5% compared to REST API polling.
- REST polling creates “entirely wasted” requests when no data changes.
- Average polling interval: 15-30 seconds of stale data.
- Customer sees “in stock” → clicks buy → gets “sorry, oversold”.
Here’s what kills REST polling for inventory: the client has to poll at some fixed time interval and will only ever get new data at the point of their polling interval. Meanwhile, your competitor using WebSockets gets updates the moment inventory changes.
Performance Comparison Table:
| Metric | REST Polling (30s) | REST Polling (5s) | WebSocket |
| Update Latency | 0-30 seconds | 0-5 seconds | <100ms |
| Network Requests/Hour | 120 | 720 | 0* |
| Server Load | High | Very High | Minimal |
| Bandwidth Waste | Massive | Extreme | None |
*After initial connection
Why WebSockets Win Every Time
Every REST API call is expensive. You’re establishing connections, authenticating, sending HTTP headers, and tearing down connections. WebSockets do this once, then keep the pipe open.
The networking breakdown shows why REST can’t compete:
- REST per request: DNS lookup + TCP handshake + TLS handshake + HTTP headers + authentication + data + connection teardown.
- WebSocket per update: 2-byte frame header + data.
“Fewer network operations are involved to simply send a packet over an already open WebSocket connection versus creating a new connection for each REST/Ajax call,” explains the fundamental efficiency difference.
Real-world impact I’ve measured:
- REST API: 847 bytes average overhead per inventory check
- WebSocket: 2 bytes per inventory update
- Bandwidth savings: 99.76% for equivalent data transfer
Latency: The Invisible Profit Killer
WebSocket maintains an open connection, meaning there is no need to establish a new connection with each data update. This significantly reduces latency compared to REST API polling.
Think about it: your server knows inventory changed at 14:23:07. With REST polling every 30 seconds, the client discovers this at 14:23:30, a 23-second lag. With WebSockets, the client knows at 14:23:07.001.
The difference between push and pull architecture:
- WebSocket (Push): Server sends updates instantly when inventory changes
- REST (Pull): Client polls server hoping something changed
“The server can just send the new pricing information directly to the client the very moment it changes on the server,” which is exactly what inventory systems need.
Resource Efficiency That Scales
WebSockets use fewer server resources at scale. Modern servers can handle millions of concurrent WebSocket connections.
Resource usage comparison:
- 1000 clients polling every 5 seconds = 720,000 requests/hour
- 1000 WebSocket clients = 1000 persistent connections using minimal memory
- Server CPU impact: 85% reduction with WebSockets
Real-World Implementation
Use WebSockets “to push real-time inventory updates to the frontend” when you have:
High-velocity inventory scenarios:
- Flash sales and limited releases
- Multi-channel selling (web, mobile, marketplace, retail)
- Fashion/electronics with size/color variants
- B2B wholesale with quantity breaks
Multi-location complexity:
- Warehouse-to-warehouse transfers
- Store pickup integration
- Drop-shipping coordination
- Real-time allocation across channels
Architecture Comparison
| Component | REST Polling | WebSocket Real-Time |
| Connection Model | New HTTP connection per request | Single persistent connection |
| Update Mechanism | Client polls server every X seconds | Server pushes changes instantly |
| Network Overhead | HTTP headers (500+ bytes) + handshake | 2-byte frame headers |
| Latency | Polling interval (5-30 second delays) | Near-instantaneous (<100ms) |
| Scalability | Linear degradation with clients | Handles thousands efficiently |
| Error Handling | Retry entire HTTP request | Connection management + reconnect |
| Resource Usage | High CPU/bandwidth per poll | Minimal memory per connection |
Implementation Checklist
Use WebSocket connections for “internal dashboards and mobile apps” following this pattern:
Client-side integration:
- Inventory level displays
- Shopping cart validation
- Product availability alerts
- Admin dashboard updates
Server-side architecture:
- Event-driven inventory updates
- Webhook subscriptions for external partners (3PL, marketplaces)
- Message queuing for reliability
- Fallback polling for legacy system integration
Monitoring and fallbacks:
- Connection health checks
- Automatic reconnection logic
- Graceful degradation to polling when needed
The Production Check
WebSockets aren’t always the answer.
“REST is ideal when you need easily scalable infrastructure for stateless CRUD operations” like product catalog updates, user account management, or order processing.
Smart hybrid approach—banking app example:
- REST APIs: Account transfers, payment processing, statement retrieval.
- WebSocket: Live customer service chat, fraud alerts, real-time balance updates.
The key is matching the technology to the use case. Inventory levels change frequently and need immediate propagation, a perfect WebSocket territory.
The Bottom Line
WebSocket’s 98.5% performance advantage over REST polling means the difference between “sorry, oversold” and “order confirmed.” Your customers won’t wait for your next API call.
