02. AWS ELB
Elastic Load Balancing (ELB) automatically distributes incoming traffic across multiple EC2 instances (targets). It improves elasticity, availability, and fault tolerance.
Load Balancer
- Acts as a single entry point (DNS hostname).
- Distributes requests across backend EC2 instances.
- Performs health checks and removes unhealthy targets.
- Supports SSL termination (HTTPS).
- Enables multi-AZ high availability.
🏗️ Architecture
Request Flow
User → Load Balancer → EC2 Instances (Targets)
- Traffic is routed only to healthy instances.
- Instances are spread across multiple AZs.
- Scaling is automatic when used with Auto Scaling Groups.
☯️ AWS-Managed vs Self-Managed Load Balancer
| Type | Description | Managed By | Maintenance Effort | Cost |
|---|---|---|---|---|
| AWS Managed ELB | Fully managed service | AWS | Low | Moderate |
| Self-Managed LB (on EC2) | Custom setup on EC2 | You | High (OS, patching, scaling) | Lower initially |
🧱 OSI Model (7 Layers)
- Layer 7 – Application: HTTP, HTTPS, DNS
- Layer 6 – Presentation: SSL/TLS, Encryption
- Layer 5 – Session: Session control
- Layer 4 – Transport: TCP, UDP
- Layer 3 – Network: IP, Routing
- Layer 2 – Data Link: MAC, Ethernet
- Layer 1 – Physical: Cables, Signals
Mnemonic: All People Seem To Need Data Processing
🌐 Types of Load Balancers in AWS
AWS provides four load balancer types:
| Load Balancer | Layer | Protocols | Key Features | Use Case |
|---|---|---|---|---|
| Application Load Balancer (ALB) | Layer 7 | HTTP, HTTPS, gRPC | Path/host-based routing | Web apps, APIs |
| Network Load Balancer (NLB) | Layer 4 | TCP, UDP | Ultra-high performance, static IP | Gaming, IoT, real-time apps |
| Gateway Load Balancer (GWLB) | Layer 3 | IP (GENEVE) | Traffic inspection & firewalling | Security appliances |
| Classic Load Balancer (CLB) (deprecated) | Layer 4 & 7 | TCP, HTTP | Legacy | — |
01. Application Load Balancer (ALB)
- Operates at Layer 7 (HTTP/HTTPS).
- Supports advanced routing (host, path, headers, query).
- Static DNS
- Uses target groups.
- Supports WebSockets and gRPC.
- Provides a static DNS name (not static IP).
🧩 Architecture (ALB)
🛠️ Use Cases
- Web applications
- REST APIs
- Microservices (ECS, EKS)
02. Network Load Balancer (NLB)
- Operates at Layer 4 (TCP/UDP).
- Handles millions of requests per second.
- Supports static IPs using Elastic IPs.
- Optimized for low latency.
🧩 Architecture (NLB)
🛠️ Use Cases
- Real-time systems
- Gaming backends
- Financial or IoT workloads
03. Gateway Load Balancer (GWLB)
- Operates at Layer 3 (IP).
- Uses GENEVE (UDP port 6081).
- Routes traffic through security appliances/firewall on EC2.
- Enables centralized traffic inspection, intrusion detection or deep packet inspeciton.
🧩 Architecture (GWLB)
🛠️ Use Cases
- Firewalls
- IDS / IPS systems
- Deep packet inspection
04. Classic Load Balancer (CLB)
⚠️ Deprecated (do not use for new workloads)
- Supports Layer 4 & 7.
- Superseded by ALB and NLB.
- Appears only in legacy architectures.
🧩 Comparison Summary
| Feature | ALB | NLB | GWLB |
|---|---|---|---|
| Layer | 7 | 4 | 3 |
| Protocol | HTTP/HTTPS/gRPC | TCP/UDP | IP (GENEVE) |
| Routing Logic | Advanced | Connection-based | Packet forwarding |
| Static IP | ❌ | ✅ | ✅ |
| SSL Termination | ✅ | ✅ | ❌ |
| Health Checks | HTTP | TCP | IP-based |
🧾 Exam Tips (CLF-C02)
| Scenario | Choose |
|---|---|
| HTTP / HTTPS routing | ALB |
| Millions of requests, ultra-low latency | NLB |
| Firewall or packet inspection | GWLB |
| Static IP required | NLB |
| Legacy architecture | CLB |