Task Statement 2.1: Design scalable and loosely coupled architectures.

📘AWS Certified Solutions Architect – (SAA-C03)

1. What Is Load Balancing?

Load balancing is the process of distributing incoming application traffic across multiple computing resources such as servers, containers, or virtual machines.

Instead of sending all user requests to a single server, a load balancer distributes them across several backend systems.

Why Load Balancing Is Important

Load balancing helps achieve:

High availability – If one server fails, others continue serving requests.
Scalability – More servers can be added when demand increases.
Fault tolerance – Failures in one component do not stop the entire system.
Better performance – Traffic is evenly distributed.
Improved reliability – Applications remain accessible during heavy traffic.

In cloud environments like Amazon Web Services, load balancing is a key architectural component.

2. Elastic Load Balancing (ELB)

In AWS, load balancing is provided by a service called Elastic Load Balancing.

Elastic Load Balancing automatically distributes incoming traffic across multiple targets.

Supported Targets

Targets can include:

EC2 instances
Containers
IP addresses
Serverless services

A target group may contain one or many backend resources.

3. Types of AWS Load Balancers

AWS provides multiple types of load balancers. For the SAA-C03 exam, you should understand the differences.

1. Application Load Balancer (ALB)

Application Load Balancer operates at Layer 7 (Application Layer) of the OSI model.

It routes requests based on HTTP/HTTPS information.

Key Capabilities

Content-based routing
Host-based routing
Path-based routing
Support for containers and microservices
Integration with container platforms

ALB is commonly used for modern web applications and microservices architectures.

2. Network Load Balancer (NLB)

Network Load Balancer operates at Layer 4 (Transport Layer).

It routes traffic based on IP protocol data (TCP/UDP).

Key characteristics:

Extremely high performance
Handles millions of requests per second
Ultra-low latency
Supports static IP addresses

Used for:

Real-time applications
High-performance systems
TCP/UDP workloads

3. Gateway Load Balancer (GWLB)

Gateway Load Balancer is designed for network security appliances.

It allows deployment of security systems such as:

Firewalls
Intrusion detection systems
Packet inspection tools

4. Classic Load Balancer (Legacy)

Classic Load Balancer is the older generation load balancer.

It supports basic Layer 4 and Layer 7 features but is mostly replaced by ALB and NLB.

4. Application Load Balancer (ALB) – Detailed Explanation

The Application Load Balancer is one of the most important services for the SAA-C03 exam.

It distributes HTTP/HTTPS requests to multiple backend targets.

5. Core Components of Application Load Balancer

1. Listener

A listener checks for incoming requests on a specific port and protocol.

Example configuration:

HTTP – Port 80
HTTPS – Port 443

When traffic arrives, the listener evaluates rules and forwards the request.

2. Listener Rules

Listener rules determine how traffic is routed.

Rules contain:

Conditions
Actions

Conditions can include:

URL path
Hostname
HTTP headers
Query parameters

Actions include:

Forward to target group
Redirect
Return fixed response

3. Target Group

A target group is a collection of backend resources that receive traffic.

Targets may include:

EC2 instances
Containers
IP addresses
Serverless functions

The load balancer sends requests only to healthy targets.

4. Targets

Targets are the actual compute resources running the application.

Examples:

Web servers
API services
Application containers

6. Health Checks

Health checks ensure that traffic is only sent to healthy resources.

The load balancer periodically checks targets using:

HTTP
HTTPS
TCP

If a target fails health checks:

It is marked unhealthy
Traffic stops being sent to it

Once the target recovers, it automatically returns to service.

7. Routing Capabilities of Application Load Balancer

ALB supports advanced routing methods.

Path-Based Routing

Requests are routed based on the URL path.

Example architecture:

/api        → API servers
/images     → image service
/login      → authentication service

This allows multiple services to run behind one load balancer.

Host-Based Routing

Requests are routed based on the domain name.

Example:

api.company.com      → API servers
app.company.com      → application servers
admin.company.com    → admin system

Header-Based Routing

Traffic can be routed based on HTTP headers.

This is useful for:

testing environments
version-based routing

8. Load Balancing Algorithms

Load balancers distribute traffic using algorithms.

Common methods include:

Round Robin

Requests are distributed sequentially:

Request 1 → Server A
Request 2 → Server B
Request 3 → Server C

Least Outstanding Requests

Traffic is sent to the server with the fewest active requests.

This helps maintain performance during uneven workloads.

9. Integration With Other AWS Services

Application Load Balancer integrates with several AWS services.

Compute Services

ALB works with:

Amazon EC2
Amazon ECS
Amazon EKS

This makes it ideal for container-based applications.

Auto Scaling

Integration with Amazon EC2 Auto Scaling allows automatic scaling.

When traffic increases:

New instances are launched
Load balancer starts sending traffic to them automatically

DNS Integration

ALB can be used with Amazon Route 53 to direct users to the load balancer.

10. High Availability With Load Balancers

AWS load balancers are automatically deployed across multiple Availability Zones.

An **Application Load Balancer:

distributes traffic across zones
continues working even if one zone fails

This ensures:

high availability
resilience
fault tolerance

11. Security Features

Application Load Balancers include multiple security features.

HTTPS Termination

The load balancer can handle SSL/TLS encryption.

Certificates can be managed using AWS Certificate Manager.

Benefits:

Encryption handled at load balancer
Backend servers handle only application logic

Integration With Security Groups

ALB supports security groups to control allowed traffic.

Example rules:

allow HTTPS traffic from internet
allow internal communication to backend servers

12. Monitoring and Logging

Load balancers can be monitored using Amazon CloudWatch.

Metrics include:

request count
latency
error rates
healthy host count

Logs can also be stored in Amazon S3 for analysis.

13. Designing Scalable Architectures With Load Balancers

Load balancers are used in scalable architectures to:

distribute user traffic
prevent server overload
improve fault tolerance
allow horizontal scaling
support microservices architectures

Typical architecture:

Users
   ↓
Route 53 (DNS)
   ↓
Application Load Balancer
   ↓
Multiple backend servers (EC2 or containers)

This design ensures that traffic is automatically distributed across multiple systems.

14. Important Exam Tips

For the SAA-C03 exam, remember the following key points:

Application Load Balancer

Works at Layer 7
Supports HTTP/HTTPS
Provides advanced routing
Ideal for microservices and container applications

Network Load Balancer

Works at Layer 4
Supports TCP/UDP
Very high performance

Gateway Load Balancer

Used for security appliances

Health Checks

Automatically remove unhealthy targets
Ensure traffic only reaches healthy systems

15. Key Takeaways

Load balancing is essential for building scalable, reliable, and highly available cloud architectures.

In AWS:

Elastic Load Balancing distributes traffic automatically
Application Load Balancer provides intelligent Layer 7 routing
Health checks improve reliability
Integration with Auto Scaling supports dynamic scaling

These concepts are critical for designing loosely coupled architectures, which is a major focus of the AWS Certified Solutions Architect – Associate (SAA-C03) exam.