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 | 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:

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:

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

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 + centraliz