Curriculum Overview: High Availability in the AWS Cloud

This document provides a comprehensive roadmap for mastering High Availability (HA) within the AWS ecosystem, focusing on designing resilient systems that minimize downtime and eliminate single points of failure.

## Prerequisites

Before starting this module, students should have a baseline understanding of the following:

• Cloud Fundamentals: Understanding the difference between on-premises and cloud computing.
• AWS Global Infrastructure: A basic awareness of Regions and Availability Zones (AZs).
• Core Compute Concepts: Familiarity with virtual servers (Amazon EC2) and their role in hosting applications.
• Basic Networking: General understanding of how traffic flows from a user to a server (IP addresses, DNS).

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## Module Breakdown

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## Learning Objectives per Module

Module 1: Foundations of HA

• Define High Availability and its relationship to Fault Tolerance (FT).
• Explain the significance of the "Five Nines" (99.999%) in service level agreements.

Module 2: Global Infrastructure

• Describe how Availability Zones are physically distinct to mitigate localized disasters.
• Map the relationship between Regions and AZs to ensure cross-zone redundancy.

Module 3: HA Compute & Elasticity

• Configure Elastic Load Balancing (ELB) to distribute traffic across multiple healthy targets.
• Differentiate between Horizontal Scaling (Elasticity) and Vertical Scaling.

Module 4: Resilient Data Layers

• Explain the Multi-AZ feature in Amazon RDS and its impact on write availability.
• Contrast Read Replicas (Performance) with Multi-AZ (High Availability).

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## Examples

[!TIP] Single Point of Failure (SPOF) vs. HA A single EC2 instance is a SPOF. Even if the hardware is reliable, if that AZ goes down, your app is offline. HA Solution: Deploy two EC2 instances in different AZs behind an ELB.

Real-World Case Studies

1. The E-Commerce Seasonal Surge

• Concept: Auto Scaling + HA.
• Example: A retailer uses Auto Scaling to add EC2 instances across three AZs during a Black Friday sale. If one AZ experiences a power failure, the Load Balancer shifts traffic to the remaining two AZs automatically.

2. The Financial Transaction Database

• Concept: RDS Multi-AZ.
• Example: A bank uses RDS Multi-AZ. When a hardware failure hits the primary database, AWS automatically fails over to the standby in a different AZ within 2 minutes. No data is lost because of synchronous replication.

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## Success Metrics

To demonstrate mastery of this curriculum, the student must achieve the following:

• Design Proficiency: Successfully draw an architecture that contains zero Single Points of Failure.
• Calculated Uptime: Correctly determine the impact of a 2-minute failover on a monthly uptime percentage.
• Tool Selection: Choose the correct AWS service (e.g., ELB vs. Auto Scaling) based on a specific failure scenario.
• Configuration: Demonstrate the ability to enable Multi-AZ in a sandbox RDS environment.

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## Real-World Application

Why High Availability Matters in Careers

In a modern DevOps or Cloud Architect role, downtime is expensive. Organizations lose thousands of dollars per minute of outage. Understanding HA allows you to:

1. Reduce Business Risk: Protect the company's reputation by ensuring services stay online during regional outages.
2. Optimize Costs: Balance the cost of redundancy against the requirement for uptime (e.g., 99.9% vs 99.99%).
3. Implement Disaster Recovery: Design systems that can survive natural disasters affecting entire geographic areas.

Comparison Table: Scalability vs. Availability