Design a 99.999% Available System | System Design Interview

Can your system survive when a data center goes down? Here's how to design a 99.999% available architecture — the exact pattern asked in FAANG interviews. In this System Design deep dive, I break down everything you need to answer "Design a High Availability System" in your next interview — from eliminating Single Points of Failure (SPOF) to choosing between Active-Active and Active-Passive architectures. 🔍 What You'll Learn: • What 99.999% availability (Five 9s) actually means in practice • Single Points of Failure — how to identify and eliminate them • Multi-node architecture with load balancers & replicated databases • Active-Active Architecture — max resource utilization, but complex writes • Active-Passive Architecture — simpler failover, but 10-15 min downtime risk • Real databases: Cassandra (multi-master) vs MySQL/PostgreSQL (active-passive) • When to use each pattern — read-heavy vs write-heavy workloads Time Stamps: 0:00 - What is High Availability Architecture? 0:10 - How This Question Gets Asked in Interviews 1:07 - What is Single Point of Failure (SPOF)? 4:19 - Multi-Node Architecture Explained 4:34 - Active-Active vs Active-Passive — Overview 4:43 - What Are Data Centers? 6:43 - Active-Passive Architecture — Deep Dive 9:47 - Why MySQL & PostgreSQL Are Active-Passive Only 10:45 - Active-Active Architecture — Deep Dive 10:55 - Cassandra — The Multi-Master Solution 12:17 - Synchronization Challenges & Conflict Resolution 12:29 - When to Use Each Architecture 13:28 - Outro Part of the System Design Interview Series on Repeat By Design — built for engineers who started from scratch and are cracking top-tier interviews step by step. #systemdesign #systemdesigninterview #softwareengineering #highavailability #interviewpreparation