Masst DocsLoad Balancer
Understanding load balancing strategies and implementations.
What is a Load Balancer?
A Load Balancer distributes incoming network traffic across multiple servers to ensure no single server bears too much load, improving reliability and performance.
Load Balancer Architecture
┌─────────────┐
│ Clients │
└──────┬──────┘
│
┌──────▼──────┐
│ Load │
│ Balancer │
└──────┬──────┘
│
┌───────────────┼───────────────┐
│ │ │
┌────▼────┐ ┌────▼────┐ ┌────▼────┐
│Server 1 │ │Server 2 │ │Server 3 │
└─────────┘ └─────────┘ └─────────┘Load Balancing Algorithms
| Algorithm | How It Works | Best For |
|---|---|---|
| Round Robin | Rotate through servers sequentially | Equal server capacity |
| Weighted Round Robin | More traffic to higher-weight servers | Varying server capacity |
| Least Connections | Route to server with fewest connections | Long-lived connections |
| IP Hash | Same client IP → same server | Session persistence |
| Least Response Time | Route to fastest responding server | Performance optimization |
Types of Load Balancers
Layer 4 (Transport)
- Operates on TCP/UDP
- Fast, simple routing
- No content inspection
Layer 7 (Application)
- Operates on HTTP/HTTPS
- Content-based routing
- Can inspect headers, cookies, URLs
Layer 7 routing example:
/api/* → API servers
/images/* → Static servers
/admin/* → Admin serversHealth Checks
Load Balancer
│
├──► Server 1: GET /health → 200 OK ✓
├──► Server 2: GET /health → 200 OK ✓
└──► Server 3: GET /health → 503 ✗ (removed from pool)High Availability
┌─────────────┐ ┌─────────────┐
│ LB │◄──►│ LB │
│ (Active) │ │ (Standby) │
└──────┬──────┘ └─────────────┘
│
Virtual IPPopular Load Balancers
| Type | Examples |
|---|---|
| Hardware | F5, Citrix ADC |
| Software | HAProxy, NGINX |
| Cloud | AWS ALB/NLB, GCP Load Balancer |
Interview Tips
- Know L4 vs L7 differences
- Explain common algorithms and when to use each
- Discuss health checks and failover
- Mention sticky sessions for stateful applications