API Gateway & Reverse Proxy Expert

Configure and optimize API gateways and reverse proxies for routing, authentication, rate limiting, and traffic management.

Decision Points

Authentication Strategy Selection

Traffic Pattern & Requirements
├── Internal services only
│   └── API Key authentication
│       ├── Low complexity, fast validation
│       └── Kong: key-auth plugin, Traefik: forwardAuth
├── Customer-facing API with session needs
│   └── JWT authentication
│       ├── Stateless, includes user claims
│       └── Kong: jwt plugin, Nginx: lua-resty-jwt
├── Enterprise B2B integration
│   └── mTLS authentication
│       ├── Certificate-based, highest security
│       └── Kong: mtls-auth, Nginx: ssl_verify_client
└── Third-party SaaS integration
    └── OAuth2 flow
        ├── Token exchange, delegated auth
        └── Kong: oauth2 plugin, AWS API Gateway: authorizer

Gateway Technology Selection

Requirements → Choice
├── Plugin ecosystem & GUI needed
│   └── Kong Enterprise/OSS
├── Kubernetes-native with auto-discovery
│   └── Traefik v3 or Ingress-NGINX
├── Maximum performance, minimal features
│   └── Nginx or Envoy
└── Cloud-managed, serverless scaling
    └── AWS API Gateway or Azure Application Gateway

Upstream Routing Strategy

Service Architecture → Routing Method
├── Microservices with service discovery
│   └── Dynamic upstream targets
│       ├── Consul/Eureka integration
│       └── Health check based load balancing
├── Static backend services
│   └── Fixed upstream pools
│       ├── Round-robin or least-connections
│       └── Weighted routing for canary deployments
└── Multi-region deployment
    └── Geographic routing
        ├── Latency-based or geo-IP
        └── Fallback to secondary regions

Failure Modes

Gateway Timeout Cascade

Symptom: Slow API responses (>10s) under load
Detection: Response times spike while upstream services report normal latency
Root Cause: Gateway timeout higher than upstream timeout, causing request queuing
Fix: Set gateway read timeout < upstream timeout (gateway: 30s, upstream: 25s)

Authentication Bypass

Symptom: Unauthorized requests reaching backend services
Detection: Backend logs show requests without expected auth headers
Root Cause: Route order allows permissive rules to match before auth rules
Fix: Move auth middleware to global level or ensure specific routes come first in config

Circuit Breaker Thrashing

Symptom: Intermittent 503 errors during traffic spikes
Detection: Circuit breaker opens/closes rapidly (multiple times per minute)
Root Cause: Threshold too sensitive or health check misconfigured
Fix: Tune failure threshold (5+ failures) and recovery time (30s minimum)

SSL Certificate Expiry

Symptom: HTTPS handshake failures, browser certificate warnings
Detection: SSL cert check shows expiry within 30 days
Root Cause: Manual certificate management without renewal automation
Fix: Implement cert-manager (K8s) or ACME client with auto-renewal

Resource Exhaustion

Symptom: Gateway stops accepting connections, memory/CPU at 100%
Detection: Connection refused errors, gateway health checks failing
Root Cause: No connection limits or memory leaks in plugins
Fix: Set worker_connections (Nginx) or connection pool limits (Kong), restart gateway

Worked Examples

Scenario: E-commerce API Gateway Setup

Context: Deploy Kong for microservices handling orders, inventory, payments with JWT auth

Step 1: Route Definition

# Identify service endpoints first
services:
  - orders: /api/v1/orders/* → http://orders:8080
  - inventory: /api/v1/inventory/* → http://inventory:8080  
  - payments: /api/v1/payments/* → http://payments:8080

Step 2: Apply Decision Tree

• Traffic pattern: Customer-facing API → JWT authentication
• Architecture: Microservices → Dynamic upstream targets
• Requirements: Plugin ecosystem needed → Kong selected

Step 3: Plugin Ordering

# Apply plugins in correct order
plugins:
  1. cors (pre-auth)
  2. jwt (authentication) 
  3. rate-limiting (post-auth)
  4. request-transformer (last)

Expert vs Novice:

• Novice mistake: Applies rate limiting before authentication (anonymous users consume quota)
• Expert approach: Auth first, then rate limit per authenticated user
• Novice mistake: Uses global CORS policy
• Expert approach: Different CORS per route (orders allows admin origins, payments restricts to frontend only)

Failure Scenario: Canary Deployment Gone Wrong

Situation: Deployed 20% traffic to new orders service version, seeing 500 errors

Detection Process:

1. Check gateway metrics: 500 rate spike correlates with deployment time
2. Upstream health checks: New version failing health checks
3. Gateway logs: Upstream connection timeouts

Rollback Procedure:

# Step 1: Immediate traffic shift
kong:
  routes:
    - service: orders-v1
      weight: 100  # Was 80
    - service: orders-v2  
      weight: 0    # Was 20

# Step 2: Validate rollback
curl -H "Authorization: Bearer $JWT" \
  https://api.company.com/orders/health

# Step 3: Remove failed upstream
kubectl scale deployment orders-v2 --replicas=0

Root Cause Analysis: New version had database connection pool misconfiguration, causing timeouts under load

Quality Gates

• All routes have explicit path matching (no catch-all /* routes)
• Authentication middleware configured before business logic plugins
• Health checks return 2xx for healthy upstreams within 5 seconds
• Circuit breaker thresholds set: 5 failures in 60s window, 30s recovery
• TLS certificates auto-renew with 30+ days before expiry
• Rate limiting applied per authenticated user, not globally
• CORS policy restricts origins to required domains only
• Gateway timeout (30s) < upstream timeout (25s) to prevent cascades
• Access logs include correlation ID for request tracing
• Gateway deployed with minimum 2 replicas for high availability

NOT-FOR Boundaries

This skill handles: Gateway configuration, routing rules, authentication middleware, reverse proxy setup

NOT for:

• Rate limiting algorithm design → Use api-rate-limiting-throttling-expert
• Service mesh data plane configuration → Use service-mesh-microservices-expert
• API specification and design → Use api-architect
• Database connection pooling → Use database-performance-expert
• Container orchestration → Use kubernetes-expert or docker-expert
• SSL certificate generation → Use security-infrastructure-expert

Delegation Rules:

• For custom rate limiting algorithms: "I'll configure the rate limiting plugin, but for custom algorithms, use api-rate-limiting-throttling-expert"
• For service discovery setup: "I'll configure upstream targets, but for service mesh setup, use service-mesh-microservices-expert"