⚖️ Load Balancing Use Cases Guide
Load balancing is critical for building scalable, resilient, and high-performing systems. Beyond basic traffic distribution, modern load balancers handle diverse use cases across infrastructure, performance, security, and user experience.
🧯 1. Failure Handling
Purpose:
Automatically redirects traffic away from failed or degraded instances to ensure continuous service.
How it works:
Load balancers detect unresponsive servers and stop routing traffic to them, avoiding downtime.
Benefits:
- High availability
- Reduced user-facing errors
- Automatic failover
// Example: NGINX marking upstream as down
upstream backend {
server backend1.example.com;
server backend2.example.com down; # temporarily disabled
}
🩺 2. Instance Health Checks
Purpose:
Ensures traffic is only sent to healthy and responsive instances.
How it works:
- Active health checks (ping, HTTP response)
- Passive checks (detect errors from previous requests)
Benefits:
- Real-time monitoring
- Prevents routing to broken services
Tools: AWS ALB/NLB, GCP Load Balancing, HAProxy, NGINX
🧠 3. Platform-Specific Routing
Purpose:
Customize responses for different platforms or devices (e.g., desktop vs mobile).
How it works:
Load balancer inspects request headers or user-agent to route accordingly.
Use Cases:
- Mobile-specific backend logic
- A/B testing across device classes
- Redirecting traffic based on capabilities
// Example: Detect platform via header
if ($http_user_agent ~* "Mobile") {
proxy_pass http://mobile_backend;
}
🔐 4. SSL Termination
Purpose:
Offloads the burden of SSL/TLS decryption from backend services.
How it works:
The load balancer handles SSL handshakes and sends decrypted HTTP to backend.
Benefits:
- Better backend performance
- Centralized certificate management
- Simplifies backend services
Common in:
NGINX, HAProxy, AWS ELB, Cloudflare, Envoy
// NGINX SSL termination
server {
listen 443 ssl;
ssl_certificate /etc/nginx/ssl.crt;
ssl_certificate_key /etc/nginx/ssl.key;
proxy_pass http://backend;
}
🌍 5. Cross-Zone Load Balancing
Purpose:
Spreads traffic evenly across multiple zones or regions.
Why it matters:
- Reduces zone-specific overload
- Resilient against zone outages
- Improves performance by geo-routing
Cloud Examples:
- AWS: Enable cross-zone load balancing in ALB
- GCP: Global load balancing by default
🧲 6. User Stickiness (Session Affinity)
Purpose:
Routes a user consistently to the same backend server.
When to use:
- Applications storing sessions in memory (no shared session store)
- Avoid disrupting user workflows mid-session
How it works:
- Cookie-based stickiness
- Source IP-based affinity
Caution:
Can cause unbalanced traffic if not managed properly.
// AWS ALB Example (Stickiness)
stickiness.enabled = true
stickiness.type = lb_cookie
📍 7. Geo-Based Routing
Purpose:
Routes users to the closest or most relevant regional instance.
Why it's useful:
- Reduces latency
- Improves compliance (e.g., data residency)
- Enhances user experience
Cloud Services:
AWS Route 53 Geolocation, Cloudflare Load Balancing, GCP Global LB
🚦 8. Rate Limiting & Traffic Shaping
Purpose:
Prevent abuse, apply quotas, or smooth traffic surges.
How it works:
- Enforce limits per IP, user, or API key
- Apply throttling to preserve backend stability
// Example: NGINX rate limiting
limit_req_zone $binary_remote_addr zone=mylimit:10m rate=10r/s;
limit_req zone=mylimit burst=20;
🧱 9. Layer 4 vs Layer 7 Load Balancing
| Feature | Layer 4 (TCP/UDP) | Layer 7 (HTTP/HTTPS) |
|---|---|---|
| Routing Criteria | IP, Port | URL path, headers, cookies |
| Flexibility | Fast, simple | Smart, flexible routing |
| Protocol Support | TCP, UDP | HTTP, gRPC, WebSockets |
| Common Tools | AWS NLB, HAProxy | NGINX, AWS ALB, Envoy |
🧪 10. Canary Deployments & A/B Testing
Purpose:
Route a small percentage of traffic to a new version of your service for testing.
How it helps:
- Minimize blast radius
- Collect feedback and metrics
- Roll back safely if needed
Implementation:
Weighted routing rules, traffic splitting (Istio, Linkerd, AWS App Mesh)
✅ Summary Table
| Use Case | Purpose |
|---|---|
| Failure Handling | Redirect traffic from failed services |
| Health Checks | Only send traffic to healthy instances |
| Platform Routing | Customize backend per device or platform |
| SSL Termination | Offload encryption/decryption workload |
| Cross-Zone Balancing | Distribute load across regions/zones |
| Session Stickiness | Maintain user session consistency |
| Geo Routing | Route users by location |
| Traffic Shaping | Control request rates and bursts |
| Layer 7 Routing | Smart HTTP-based routing |
| Canary / A/B Testing | Test new versions with limited exposure |
🧠 Further Reading
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