Tutorials System Design Tutorial
High Availability System Patterns — Complete Guide
High Availability System Patterns — Complete Guide: free step-by-step lesson with examples, common mistakes, and interview tips — part of System Design Tutorial on Toolliyo Academy.
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System Design Tutorial · Lesson 88 of 100
High Availability System Patterns
Basics ✓ → Scale ✓ → Interview
Interview · 3 — Case studies · ~10 min · Module 9: Performance and Optimization
What is this?
HA patterns remove single points of failure — redundant instances, multi-AZ, health-checked failover, and quorum where needed.
Why should you care?
One ShopNest API VM dying should not zero the site.
See it live — copy this example
Sketch the architecture on paper. These lessons focus on concepts and trade-offs.
Multi-AZ API + LB
DB primary + failover replica
Cache with replica
Quorum for consensus systems
Avoid: single NAT/bastion as silent SPOFRun Example »
This lesson uses terminal or setup steps. Run commands on your computer — the live editor appears on coding lessons.
What happened?
- Redundancy plus automatic failover beats manual heroics.
- Hunt SPOFs beyond the obvious app tier — including network boxes.
Practice next
- List ShopNest SPOFs.
- Put APIs in ≥2 AZs behind LB.
- Enable DB failover.
- Add PDB so deploys do not drain all checkout pods.
- Dual NAT gateways.
Remember
Eliminate SPOFs. Multi-AZ + health checks. Test failover.
Multi-AZ ShopNest
One AZ outage; LB drains bad targets.
Outcome: Customers keep shopping on healthy AZs.
Interview prep for this lesson
Practice these questions aloud after reading—each links to a full structured answer.
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