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🌐 Traffic Routing Components

In modern system architecture, it's crucial to understand the differences and overlaps between reverse proxies, API gateways, and load balancers. These components handle traffic routing, improve performance, enforce policies, and increase system resilience — but serve different roles.

🧭 Overview: Key Concepts

Component	Primary Role	Operates At
Load Balancer	Distributes traffic across servers	Network / Transport
Reverse Proxy	Intercepts and forwards client requests	Application Layer
API Gateway	Manages, routes, and secures API requests	Application Layer
Forward Proxy	Client-side proxy for outbound traffic	Client-Side
Ingress Controller	Manages external access to Kubernetes services	Kubernetes Layer

⚖️ Load Balancer

🧠 What It Does

A Load Balancer spreads incoming traffic across multiple backend servers to maximize performance, ensure high availability, and avoid overloading any single server.

🔧 Types

Layer 4 (Transport): Balances based on IP/port (TCP/UDP)
Layer 7 (Application): Balances based on HTTP headers, cookies, paths

// Example NGINX L7 Load Balancer
http {
  upstream backend {
    server app1.example.com;
    server app2.example.com;
  }

  server {
    listen 80;

    location / {
      proxy_pass http://backend;
    }
  }
}

✅ Use Cases

Distribute web traffic
Scale horizontal server fleets
Ensure HA across zones or regions

🔄 Reverse Proxy

🧠 What It Does

A Reverse Proxy sits in front of one or more servers and forwards client requests to them. It hides backend implementation details, can cache responses, and terminate SSL.

// Example: NGINX reverse proxy
server {
  listen 80;

  location / {
    proxy_pass http://localhost:3000;
  }
}

✅ Use Cases

SSL termination
Load balancing
Caching
URL/path rewriting
Security enforcement

🔎 NGINX and HAProxy are often used as both reverse proxies and load balancers.

🚪 API Gateway

🧠 What It Does

An API Gateway is a specialized reverse proxy that manages and routes API traffic. It often includes features like authentication, rate limiting, logging, and API versioning.

// Example: API Gateway routes
/api/v1/users → users-service
/api/v1/orders → orders-service

✨ Features

Request/response transformation
API key and token validation (OAuth2, JWT)
Quotas and throttling
Monitoring and analytics
CORS handling
Header injection

🧰 Examples

Kong, AWS API Gateway, Apigee, Traefik, Istio, Zuul

🕵️ Forward Proxy (Bonus)

🧠 What It Does

Unlike a reverse proxy, a Forward Proxy is used by clients to access external resources. It acts on behalf of the client.

Client → Forward Proxy → Internet

✅ Use Cases

Content filtering (corporate firewalls)
Access control
Anonymity (Tor, VPNs)

☸️ Ingress Controller (Kubernetes-Specific)

🧠 What It Does

A Kubernetes Ingress Controller is a reverse proxy that handles incoming HTTP/HTTPS traffic and routes it to services in the cluster.

// Example ingress route
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: app-ingress
spec:
  rules:
    - host: app.example.com
      http:
        paths:
          - path: /
            backend:
              service:
                name: my-service
                port:
                  number: 80

🧠 Key Differences

Feature/Role	Load Balancer	Reverse Proxy	API Gateway
Primary Role	Distribute traffic	Forward HTTP requests	Manage API traffic
Layer	L4/L7	L7	L7
Can modify requests	❌ (L4), ✅ (L7)	✅	✅ (extensively)
Authentication	❌	⚠️ Limited	✅ Built-in
Caching	❌ (usually)	✅	✅
API versioning	❌	❌	✅
Protocol support	TCP/UDP/HTTP	HTTP(S)	HTTP(S), gRPC

🔥 Real-World Examples

Use Case	Solution
Distribute user requests to 5 web servers	AWS ELB, HAProxy, NGINX (Load Balancer)
Route `/api/*` to microservices	Kong, Traefik, AWS API Gateway
Proxy HTTPS to an internal app	NGINX, Envoy (Reverse Proxy)
Control outbound traffic from VMs	Squid (Forward Proxy)
Route external traffic into K8s services	Ingress Controller (NGINX, Traefik)

🛠️ When to Use What

Goal	Use This
Distribute load	Load Balancer
Secure and cache static assets	Reverse Proxy
Expose, secure, and manage APIs	API Gateway
Control client access to the internet	Forward Proxy
Manage traffic inside Kubernetes	Ingress Controller

📚 Resources

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