What is Availability vs Reliability?
Updated Apr 28, 2026
Short answer
Availability is the percentage of time a system is operational; Reliability is the probability it performs as expected without failure.
Deep explanation
Availability and Reliability are the cornerstones of production-grade systems. Availability is the percentage of time a system is operational; Reliability is the probability it performs as expected without failure. Ensuring high uptime requires both preventing failures and minimizing recovery time.
Real-world example
A website staying up during a traffic spike by using multiple servers.
Common mistakes
- Assuming a system is reliable just because it is available (e.g., it's 'up' but returns errors).
Follow-up questions
- How many minutes of downtime is 99.99% availability?