Task Statement 4.2: Design cost-optimized compute solutions.

📘AWS Certified Solutions Architect – (SAA-C03)

1. What is Load Balancing?

A load balancer distributes incoming traffic (requests) across multiple servers (targets) to:

Improve availability
Increase scalability
Prevent overloading a single server
Ensure high performance

In AWS, load balancing is provided by Elastic Load Balancing (ELB).

2. Types of AWS Load Balancers

There are three main types:

1. Application Load Balancer (ALB) → Layer 7

2. Network Load Balancer (NLB) → Layer 4

3. Gateway Load Balancer (GWLB) → Layer 3 + 4 (specialized)

3. Understanding OSI Layers (Simple Explanation)

Layer 7 (Application Layer) → Understands HTTP/HTTPS content (URLs, headers)
Layer 4 (Transport Layer) → Works with TCP/UDP only (no content awareness)

👉 This difference is critical for the exam

4. Application Load Balancer (ALB) – Layer 7

Key Idea:

ALB works at the application level and can make decisions based on the content of the request.

Features:

Supports HTTP, HTTPS, WebSocket
Performs content-based routing
Supports path-based routing
Supports host-based routing
Integrates with:
- Containers (ECS, EKS)
- Microservices
Supports authentication (e.g., Cognito)
Supports redirects and fixed responses

Routing Capabilities

ALB can route traffic based on:

URL path:
- /api → backend service A
- /images → backend service B
Hostname:
- app.example.com → app servers
- admin.example.com → admin servers

When to Use ALB

Use ALB when:

You need advanced routing rules
Application uses HTTP/HTTPS
You are using:
- Microservices architecture
- Containers (ECS/EKS)
You need user authentication at load balancer level
You want cost optimization for HTTP workloads

Exam Tip

👉 If the question mentions:

URL-based routing
Microservices
HTTP/HTTPS

➡️ Answer = ALB

5. Network Load Balancer (NLB) – Layer 4

Key Idea:

NLB works at the transport layer and handles traffic based only on:

IP address
Port number

It does NOT inspect application content.

Features:

Supports:
- TCP
- UDP
- TLS
Extremely high performance
Handles millions of requests per second
Provides ultra-low latency
Supports static IP addresses
Supports Elastic IP assignment
Preserves source IP address

When to Use NLB

Use NLB when:

You need very high performance
You need low latency
You need static IP addresses
You are using:
- Non-HTTP protocols (TCP/UDP)
You need to preserve client IP

Exam Tip

👉 If the question mentions:

TCP or UDP traffic
Static IP
High throughput
Low latency

➡️ Answer = NLB

6. Gateway Load Balancer (GWLB)

Key Idea:

GWLB is used for network security and inspection.

It distributes traffic to security appliances.

Features:

Works with:
- Firewalls
- Intrusion Detection Systems (IDS)
- Intrusion Prevention Systems (IPS)
Uses GENEVE protocol
Transparent to applications
Provides centralized security management

When to Use GWLB

Use GWLB when:

You need deep packet inspection
You are deploying:
- Firewalls
- Security appliances
You want centralized security architecture

Exam Tip

👉 If the question mentions:

Firewall appliances
Traffic inspection
Security layer

➡️ Answer = GWLB

7. Key Differences (Very Important for Exam)

Feature	ALB	NLB	GWLB
OSI Layer	Layer 7	Layer 4	Layer 3/4
Protocols	HTTP, HTTPS	TCP, UDP, TLS	IP-based
Routing Type	Content-based	IP/Port-based	Security routing
Performance	High	Very High	High
Latency	Low	Ultra-low	Moderate
Static IP	No	Yes	Yes
Use Case	Web apps	High-performance apps	Security appliances

8. Cost Optimization Considerations

ALB:

Cost-effective for HTTP/HTTPS applications
Reduces need for complex application logic
Charged per request + time

NLB:

Better for high-throughput workloads
Efficient for long-lived connections
Charged per LCU (Load Balancer Capacity Unit)

GWLB:

Used only when security inspection is required
Adds cost due to additional appliances

9. How to Choose the Right Load Balancer (Decision Guide)

Choose ALB if:

You need intelligent routing
Application is web-based
You are using microservices or containers

Choose NLB if:

You need maximum performance
You require static IP
You use non-HTTP protocols

Choose GWLB if:

You need security inspection
You are deploying network appliances

10. Common Exam Scenarios

Scenario 1:

Application needs routing based on /api and /images
➡️ ALB

Scenario 2:

Application requires handling millions of TCP requests with low latency
➡️ NLB

Scenario 3:

Traffic must pass through a firewall appliance before reaching servers
➡️ GWLB

Scenario 4:

Need to preserve client IP and use static IP
➡️ NLB

Scenario 5:

Microservices running on containers
➡️ ALB

11. Final Exam Tips (Very Important)

Layer 7 = ALB = smart routing
Layer 4 = NLB = speed + performance
Security appliances = GWLB

👉 Always identify:

Protocol (HTTP vs TCP)
Routing complexity
Performance requirement
Security requirement

Conclusion

To pass this topic in the exam, remember:

ALB → Best for web applications and intelligent routing
NLB → Best for performance and low-level traffic handling
GWLB → Best for security and inspection