> Term

High Availability

A characteristic of a system that aims to ensure an agreed level of operational performance.

Detailed Explanation

High Availability (HA) refers to systems that are designed to operate continuously without failing for a designated period. It is usually measured in 'nines' (e.g., 99.99% uptime).

HA is achieved by eliminating single points of failure, establishing redundant components (servers, databases, network routes), and implementing automated failover mechanisms so the system can recover before users notice an issue.

Why It Matters

For business-critical applications, downtime translates directly to lost revenue, damaged reputation, and breached Service Level Agreements (SLAs).

Common Failure Mode

Failing to test the failover mechanism. The primary database crashes, but the automated promotion of the replica fails due to a misconfiguration, resulting in extended downtime anyway.

Practical Example

A payment gateway uses multiple instances across three AWS Availability Zones. When an entire AZ goes down due to a power outage, the load balancer instantly shifts all traffic to the surviving zones.

Production Manifestation

Deploying services across multiple Availability Zones (AZs), using active-passive database clusters, and routing traffic through highly available load balancers.

Frequently Asked Questions

What is High Availability in short?

A characteristic of a system that aims to ensure an agreed level of operational performance.

What is the most common failure mode?

Failing to test the failover mechanism. The primary database crashes, but the automated promotion of the replica fails due to a misconfiguration, resulting in extended downtime anyway.

AI Summary

A characteristic of a system that aims to ensure an agreed level of operational performance. For business-critical applications, downtime translates directly to lost revenue, damaged reputation, and breached Service Level Agreements (SLAs).