Load balancing concepts (for example, Application Load Balancer)

Task Statement 3.4: Determine high-performing and/or scalable network architectures.

📘AWS Certified Solutions Architect – (SAA-C03)

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1. What is Load Balancing?

In cloud networking, load balancing is a way to distribute incoming traffic (requests) across multiple servers or resources to ensure:

• High availability – If one server fails, others handle the traffic.
• Scalability – Can handle more traffic by adding more servers.
• Better performance – Requests are spread evenly, avoiding overload.

In AWS, load balancing is provided by Elastic Load Balancing (ELB). ELB automatically distributes incoming application or network traffic across multiple targets, like:

• EC2 instances
• Containers
• IP addresses
• Lambda functions

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2. Types of AWS Load Balancers

AWS provides three main types of load balancers:

Load Balancer Type	Layer	Use Case	Key Points
Application Load Balancer (ALB)	Layer 7 (HTTP/HTTPS)	Web applications, microservices	Can route based on URL path, host, headers, or HTTP methods; supports WebSockets
Network Load Balancer (NLB)	Layer 4 (TCP/UDP)	High-performance, low-latency apps	Handles millions of requests per second, static IP support
Gateway Load Balancer (GLB)	Layer 3 (IP)	Network appliances like firewalls	Transparent traffic inspection, scales appliance clusters

For this exam, Application Load Balancer (ALB) is the primary focus.

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3. Application Load Balancer (ALB)

Key Features of ALB

1. Layer 7 Routing
   ALB can inspect the content of requests and route them based on:
   • URL paths (e.g., /images → server group A, /api → server group B)
   • Host headers (e.g., app.example.com → server group C)
   • HTTP methods (GET, POST, etc.)
   • Query strings or source IPs
2. Target Groups
   ALB sends traffic to target groups, which are collections of resources such as:
   • EC2 instances
   • IP addresses
   • Lambda functions
   Target groups allow flexible scaling and management of resources.
3. Health Checks
   ALB automatically checks the health of each target.
   • Unhealthy targets are removed from traffic routing.
   • Healthy targets continue receiving traffic.
   • Helps ensure high availability.
4. Security
   • Works with AWS Certificate Manager (ACM) to handle HTTPS/TLS.
   • Integrates with security groups and IAM roles.
   • Supports user authentication with Cognito or OIDC providers.
5. Sticky Sessions (Optional)
   • Can route multiple requests from the same user to the same server.
   • Useful for sessions that require maintaining state in memory.
6. Cross-Zone Load Balancing
   • Can distribute traffic evenly across multiple Availability Zones (AZs).
   • Ensures high availability even if one AZ fails.
7. WebSockets and HTTP/2 Support
   • Supports modern protocols for real-time communication and better performance.

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4. How ALB Works Step-by-Step

1. User sends a request (HTTP/HTTPS) to ALB.
2. ALB checks listener rules (port and protocol) and routing rules.
3. ALB evaluates host-based or path-based rules.
4. ALB forwards request to healthy targets in the corresponding target group.
5. Target processes the request and responds.
6. ALB sends the response back to the user.

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5. Key Exam Points to Remember

• ALB works at Layer 7 (HTTP/HTTPS), unlike NLB (Layer 4).
• ALB supports content-based routing.
• ALB requires listeners (port + protocol) and target groups.
• Health checks are critical – unhealthy targets are removed automatically.
• ALB can scale automatically with traffic.
• Can integrate with WAF (Web Application Firewall) for security.

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6. Comparison: ALB vs NLB (for exam purposes)

Feature	ALB	NLB
OSI Layer	Layer 7	Layer 4
Routing	URL, host, headers, HTTP methods	TCP/UDP only
Use Case	Web apps, microservices	High-performance TCP apps
Protocols	HTTP, HTTPS, WebSockets	TCP, UDP
Target Types	EC2, Lambda, IP	EC2, IP
Sticky Sessions	Yes	No

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7. Best Practices for High-Performance and Scalable Architecture

• Deploy across multiple AZs for high availability.
• Enable health checks to prevent routing to failing targets.
• Use auto-scaling groups with ALB for dynamic scalability.
• Enable logging (ALB access logs) for monitoring traffic.
• Consider caching and CDN (CloudFront) with ALB for faster responses.

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✅ Summary for Exam:

• Know what ALB is and its Layer 7 features.
• Understand target groups, listeners, and health checks.
• Remember routing rules (path-based, host-based, method-based).
• Know ALB vs NLB differences.
• Remember high availability and scalability features like multi-AZ deployment and auto-scaling.