Availability Patterns: Active-Passive vs. Active-Active

Issue #112: System Design Interview Roadmap • Section 5: Reliability & Resilience

What We'll Build Today

In this hands-on lesson, you'll create a complete demonstration system featuring:

• Interactive Web Dashboard - Real-time visualization of both availability patterns

• Active-Passive Setup - Primary server with standby backup and automatic failover

• Active-Active Setup - Load-balanced nodes sharing traffic equally

• Failure Simulation - Click-button failure scenarios to see patterns in action

• Live Metrics - Request counts, response times, and availability percentages

• Load Balancers - nginx configurations for both patterns

By the end, you'll understand exactly when to choose each pattern and see their real-world trade-offs in action.

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The Split-Second Decision That Cost $50 Million

When a major streaming platform's primary data center went down during the season finale of their most popular show, their active-passive setup took 47 seconds to detect the failure and switch to the backup. Those 47 seconds translated to 8 million frustrated viewers and a cascade of social media complaints that damaged their brand for months.

The competitor across the street? Their active-active architecture kept streaming without missing a beat. Users never knew anything happened.

Today, we'll dissect these two fundamental availability patterns that separate resilient systems from fragile ones, and you'll build both to understand their real-world trade-offs.

What We'll Master Today

Understanding when your system needs instant failover versus cost-effective redundancy, implementing health checks that actually detect meaningful failures, and designing for the failure scenarios that matter most to your users.

Active-Passive: The Sleeping Giant Pattern