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 | Varying workloads |

Health Check Types

Shallow (Liveness): Is the process alive?

• Endpoint: /health/live or /live
• Returns: 200 if process running
• Use for: Process monitoring, container health

Deep (Readiness): Can the service handle requests?

• Endpoint: /health/ready or /ready
• Validates: Database, cache, external API connectivity
• Use for: Load balancer routing decisions

Health Check Hysteresis: Different thresholds for marking up vs down to prevent flapping

• Example: 3 failures to mark down, 2 successes to mark up

For complete health check implementation patterns, see references/health-check-strategies.md.

Cloud Load Balancers

AWS Load Balancing

Application Load Balancer (ALB) - Layer 7:

• Use for: HTTP/HTTPS applications, microservices, WebSocket
• Features: Path/host/header routing, AWS WAF integration, Lambda targets
• Choose when: Content-based routing needed

Network Load Balancer (NLB) - Layer 4:

• Use for: Ultra-low latency (<1ms), TCP/UDP, static IPs, millions RPS
• Features: Preserves source IP, TLS termination
• Choose when: Non-HTTP protocols, performance critical

Global Accelerator - Layer 4 Global:

• Use for: Multi-region applications, global users, DDoS protection
• Features: Anycast IPs, automatic regional failover

GCP Load Balancing

Application LB (L7): Global HTTPS LB, Cloud CDN integration, Cloud Armor (WAF/DDoS) Network LB (L4): Regional TCP/UDP, pass-through balancing, session affinity Cloud Load Balancing: Single anycast IP, global distribution, backend buckets

Azure Load Balancing

Application Gateway (L7): WAF integration, URL-based routing, SSL termination, autoscaling Load Balancer (L4): Basic and Standard SKUs, health probes, HA ports Traffic Manager (Global): DNS-based routing (priority, weighted, performance, geographic)

For complete cloud provider configurations and Terraform examples, see references/cloud-load-balancers.md.

Self-Managed Load Balancers

NGINX

Best for: General-purpose HTTP/HTTPS load balancing, web application stacks

Capabilities:

• HTTP reverse proxy with multiple algorithms
• TCP/UDP stream load balancing
• SSL/TLS termination
• Passive health checks (open source), active health checks (NGINX Plus)
• Cookie-based sticky sessions (NGINX Plus)

Basic configuration:

nginx
upstream backend {
    least_conn;
    server backend1.example.com:8080 weight=3;
    server backend2.example.com:8080 weight=2;
    keepalive 32;
}

server {
    listen 80;
    location / {
        proxy_pass http://backend;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

For complete NGINX patterns and advanced configurations, see references/nginx-patterns.md.

HAProxy

Best for: Maximum performance, database load balancing, resource efficiency

Capabilities:

• Highest raw throughput, lowest memory footprint
• 10+ load balancing algorithms
• Sophisticated health checks (HTTP, TCP, Redis, MySQL, etc.)
• Cookie or IP-based persistence

Basic configuration:

haproxy
frontend http_front
    bind *:80
    default_backend web_servers

backend web_servers
    balance roundrobin
    option httpchk GET /health
    server web1 192.168.1.101:8080 check
    server web2 192.168.1.102:8080 check

For complete HAProxy patterns, see references/haproxy-patterns.md.

Envoy

Best for: Microservices, Kubernetes, service mesh integration

Capabilities:

• Cloud-native design with dynamic configuration (xDS APIs)
• Circuit breakers, retries, timeouts
• Advanced health checks (TCP, HTTP, gRPC)
• Excellent observability

For complete Envoy patterns, see references/envoy-patterns.md.

Traefik

Best for: Docker/Kubernetes environments, dynamic configuration, ease of use

Capabilities:

• Automatic service discovery
• Native Kubernetes integration
• Built-in Let's Encrypt support
• Middleware system (auth, rate limiting)

For complete Traefik patterns, see references/traefik-patterns.md.

Kubernetes Ingress Controllers

Selection Guide

| Controller | Best For | Strengths | |------------|----------|-----------| | NGINX Ingress (F5) | General purpose | Stability, wide adoption, mature features | | Traefik | Dynamic environments | Easy configuration, service discovery | | HAProxy Ingress | High performance | Advanced L7 routing, reliability | | Envoy (Contour/Gateway) | Service mesh | Rich L7 features, extensibility | | Kong | API-heavy apps | JWT auth, rate limiting, plugins | | Cloud Provider | Single-cloud | Native cloud integration |

Basic Ingress Example

yaml
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: app-ingress
  annotations:
    nginx.ingress.kubernetes.io/ssl-redirect: "true"
    nginx.ingress.kubernetes.io/affinity: "cookie"
spec:
  ingressClassName: nginx
  tls:
  - hosts:
    - app.example.com
    secretName: app-tls
  rules:
  - host: app.example.com
    http:
      paths:
      - path: /api
        pathType: Prefix
        backend:
          service:
            name: api-service
            port:
              number: 80
      - path: /
        pathType: Prefix
        backend:
          service:
            name: web-service
            port:
              number: 80

For complete Kubernetes ingress examples and Gateway API patterns, see references/kubernetes-ingress.md.

Session Persistence

Sticky Sessions (Use Sparingly)

Cookie-Based: Load balancer sets cookie to track server affinity

• Accurate routing, works with NAT/proxies
• HTTP only, adds cookie overhead

IP Hash: Hash client IP to select backend server

• No cookie required, works for non-HTTP
• Poor distribution with NAT/proxies

Drawbacks: Uneven load distribution, session lost on server failure, complicates scaling

Shared Session Store (Recommended)

Architecture: Stateless application servers + centralized session storage (Redis, Memcached)

Benefits:

• No sticky sessions needed
• True load balancing
• Server failures don't lose sessions
• Horizontal scaling trivial

Client-Side Tokens (Best for APIs)

JWT (JSON Web Tokens): Server generates signed token, client stores and sends with requests

Benefits:

• Fully stateless servers
• Perfect load balancing
• No session storage needed

For complete session management patterns and code examples, see references/session-persistence.md.

Global Load Balancing

GeoDNS Routing

Route users to nearest server based on geographic location:

• DNS returns different IPs based on client location
• Reduces latency, supports compliance and regional content
• Implementation: AWS Route 53, GCP Cloud DNS, Azure Traffic Manager

Multi-Region Failover

Primary/secondary region configuration:

• Health checks determine primary region health
• Automatic DNS failover to secondary
• Transparent to clients

CDN Integration

Combine load balancing with CDN:

• GeoDNS routes to closest CDN PoP
• CDN caches content globally
• Origin load balancing for cache misses

For complete global load balancing examples with Terraform, see references/global-load-balancing.md.

Decision Frameworks

L4 vs L7 Selection

Choose L4 when:

• Protocol is TCP/UDP (not HTTP)
• Ultra-low latency critical (<1ms)
• High throughput required (millions RPS)
• Client source IP preservation needed

Choose L7 when:

• Protocol is HTTP/HTTPS
• Content-based routing needed (URL, headers)
• SSL termination required
• WAF integration needed
• Microservices architecture

Cloud vs Self-Managed

Choose Cloud-Managed when:

• Single cloud deployment
• Auto-scaling required
• Team lacks load balancer expertise
• Managed service preferred

Choose Self-Managed when:

• Multi-cloud or hybrid deployment
• Advanced routing requirements
• Cost optimization important
• Full control needed
• Vendor lock-in avoidance

Self-Managed Selection

• NGINX: General-purpose, web stacks, HTTP/3 support
• HAProxy: Maximum performance, database LB, lowest resource usage
• Envoy: Microservices, service mesh, dynamic configuration
• Traefik: Docker/Kubernetes, automatic discovery, easy configuration

Configuration Examples

Complete working examples available in examples/ directory:

Cloud Providers:

• examples/aws/alb-terraform.tf - AWS ALB with path-based routing
• examples/aws/nlb-terraform.tf - AWS NLB for TCP load balancing

Self-Managed:

• examples/nginx/http-load-balancing.conf - NGINX HTTP reverse proxy
• examples/haproxy/http-lb.cfg - HAProxy configuration
• examples/envoy/basic-lb.yaml - Envoy cluster configuration
• examples/traefik/kubernetes-ingress.yaml - Traefik IngressRoute

Kubernetes:

• examples/kubernetes/nginx-ingress.yaml - NGINX Ingress with TLS
• examples/kubernetes/traefik-ingress.yaml - Traefik IngressRoute
• examples/kubernetes/gateway-api.yaml - Gateway API configuration

Monitoring and Observability

Key Metrics

Throughput: Requests per second, bytes transferred, connection rate Latency: Request duration (p50, p95, p99), backend response time, SSL handshake time Errors: HTTP error rates (4xx, 5xx), backend connection failures, health check failures Resource Utilization: CPU, memory, active connections, connection queue depth Health: Healthy/unhealthy backend count, health check success rate

Load Balancer Logs

Enable access logs for request/response details, client IPs, response times, error tracking

• AWS ALB: Store in S3, analyze with Athena
• NGINX: Custom log format, ship to centralized logging
• HAProxy: Syslog integration, structured logging

Troubleshooting

Uneven Load Distribution

Symptoms: One server receives disproportionate traffic Causes: Sticky sessions with few clients, IP hash with NAT concentration, long-lived connections Solutions: Switch to least connections, disable sticky sessions, implement connection draining

Health Check Flapping

Symptoms: Servers rapidly transition between healthy/unhealthy Causes: Health check timeout too short, threshold too low, network instability Solutions: Increase interval and timeout, implement hysteresis, use deep health checks

Session Loss After Failover

Symptoms: Users logged out when server fails Causes: Sticky sessions without replication, in-memory sessions Solutions: Implement shared session store (Redis), use client-side tokens (JWT)

Integration Points

Related Skills:

• infrastructure-as-code - Deploy load balancers via Terraform/Pulumi
• kubernetes-operations - Ingress controllers for K8s traffic management
• network-architecture - Network design and topology for load balancing
• deploying-applications - Blue-green and canary deployments via load balancers
• observability - Load balancer metrics, access logs, distributed tracing
• security-hardening - WAF integration, rate limiting, DDoS protection
• service-mesh - Envoy as both ingress and service mesh proxy
• implementing-tls - TLS termination and certificate management

Quick Reference

Selection Matrix

| Use Case | Recommended Solution | |----------|---------------------| | HTTP web app (AWS) | ALB | | Non-HTTP protocol (AWS) | NLB | | Kubernetes HTTP ingress | NGINX Ingress or Traefik | | Maximum performance | HAProxy | | Service mesh | Envoy | | Docker Swarm | Traefik | | Multi-cloud portable | NGINX or HAProxy | | Global distribution | CloudFlare, AWS Global Accelerator |

Algorithm Selection

| Traffic Pattern | Algorithm | |-----------------|-----------| | Stateless, similar servers | Round Robin | | Stateless, different capacity | Weighted Round Robin | | Long-lived connections | Least Connections | | Performance-sensitive | Least Response Time | | Session persistence needed | IP Hash or Cookie | | Varying server load | Resource-Based |

Health Check Configuration

| Service Type | Check Type | Interval | Timeout | |--------------|------------|----------|---------| | Web app | HTTP /health | 10s | 3s | | API | HTTP /health/ready | 10s | 5s | | Database | TCP connect | 5s | 2s | | Critical service | HTTP deep check | 5s | 3s | | Background worker | HTTP /live | 30s | 5s |

Summary

Load balancing is essential for distributing traffic, ensuring high availability, and enabling horizontal scaling. Choose L4 for raw performance and non-HTTP protocols, L7 for intelligent content-based routing. Prefer cloud-managed load balancers for simplicity and auto-scaling, self-managed for multi-cloud portability and advanced features. Implement proper health checks with hysteresis, avoid sticky sessions when possible, and monitor key metrics continuously.

For deployment patterns, see examples in examples/aws/, examples/nginx/, examples/kubernetes/, and other provider directories.