AWS Solutions Architect Online Training with Certification - Visualpath
                     Elastic Load Balancing in Multi-Tier Architecture
Efficient Traffic Distribution and High Availability
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Introduction to Multi-Tier Architecture
 Definition of Multi-Tier Architecture
o A layered approach where each tier (e.g., web, application, database) serves a 
specific function.
 Example:
o Web Tier: User interface and web requests.
o Application Tier: Business logic and processing.
o Database Tier: Data storage and retrieval.
 Importance:
• Scalability, redundancy, and improved fault tolerance.
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What is Elastic Load Balancing (ELB)?
 Definition:
o ELB automatically distributes incoming application 
traffic across multiple targets (e.g., EC2 instances, 
containers).
 Types of ELB:
oApplication Load Balancer (ALB)
oNetwork Load Balancer (NLB)
• Classic Load Balancer (CLB)
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Role of ELB in Multi-Tier Architecture
 Traffic Distribution:
o Distributes incoming traffic across multiple tiers, ensuring no single 
resource is overloaded.
 High Availability:
o Ensures resources are available by rerouting traffic in case of failures.
 Scalability:
• Automatically adjusts traffic distribution as servers scale up or down.
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Benefits of ELB in Multi-Tier Architecture
 Improved Performance:
o Minimizes latency and improves application responsiveness.
 Fault Tolerance:
o Routes traffic away from unhealthy resources, improving uptime.
 Security:
o Integrates with security features (e.g., SSL termination, 
AWS WAF).
 Simplified Maintenance:
 Reduces downtime during maintenance or deployment processes.
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How ELB Works in a Multi-Tier Setup
 Traffic Flow:
1. Client sends request to the web tier.
2. Web tier forwards the request to the application tier via ELB.
3. Application tier interacts with the database tier.
 ELB’s Role:
• Balances load at each layer, ensuring seamless communication 
between tiers.
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Types of Load Balancers in Multi-Tier Architectures
 Application Load Balancer (ALB):
o Best for HTTP/HTTPS traffic.
oWorks at the application layer (Layer 7).
o Supports path-based and host-based routing.
 Network Load Balancer (NLB):
o Best for high-performance, low-latency applications.
oOperates at the network layer (Layer 4).
 Classic Load Balancer (CLB):
• Older type, supports both Layer 4 and Layer 7.
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Example Architecture with ELB
 Diagram:
o Illustrate a multi-tier architecture with ELB at each layer (web, 
application, database).
o Show how traffic flows through each layer and is balanced by ELB.
 Explanation:
• ELB ensures optimal traffic routing, maintaining high availability across 
all layers.
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Conclusion and Best Practices
Summary:
o ELB ensures that a multi-tier architecture scales efficiently, maintains high 
availability, and improves performance.
Best Practices:
oUse ALB for HTTP/HTTPS-based applications.
o Implement health checks at each tier for automatic rerouting.
o Combine ELB with auto-scaling groups for dynamic traffic management.
Final Thought:
• Elastic Load Balancing is crucial for managing complex, scalable, and highly 
available applications in a multi-tier setup.
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