load-balancing-patterns

# Load Balancing Patterns

Distribute traffic across infrastructure using the appropriate load balancing approach, from simple round-robin to global multi-region failover.

## When to Use This Skill

Use load-balancing-patterns when:
- Distributing traffic across multiple application servers
- Implementing high availability and failover
- Routing traffic based on URLs, headers, or geographic location
- Managing session persistence across stateless backends
- Deploying applications to Kubernetes clusters
- Configuring global traffic management across regions
- Implementing zero-downtime deployments (blue-green, canary)
- Selecting between cloud-managed and self-managed load balancers

## Core Load Balancing Concepts

### Layer 4 vs Layer 7

**Layer 4 (L4) - Transport Layer:**
- Routes based on IP address and port (TCP/UDP packets)
- No application data inspection, lower latency, higher throughput
- Protocol agnostic, preserves client IP addresses
- Use for: Database connections, video streaming, gaming, financial transactions, non-HTTP protocols

**Layer 7 (L7) - Application Layer:**
- Routes based on HTTP URLs, headers, cookies, request body
- Full application data visibility, SSL/TLS termination, caching, WAF integration
- Content-based routing capabilities
- Use for: Web applications, REST APIs, microservices, GraphQL endpoints, complex routing logic

For detailed comparison including performance benchmarks and hybrid approaches, see `references/l4-vs-l7-comparison.md`.

### Load Balancing Algorithms

| Algorithm | Distribution Method | Use Case |
|-----------|-------------------|----------|
| **Round Robin** | Sequential | Stateless, similar servers |
| **Weighted Round Robin** | Capacity-based | Different server specs |
| **Least Connections** | Fewest active connections | Long-lived connections |
| **Least Response Time** | Fastest server | Performance-sensitive |
| **IP Hash** | Client IP-based | Session persistence |
| **Resource-Based** | CPU/memory metrics