Reliability

The ability of a system to perform correctly and consistently over time despite expected faults or operating conditions.

Motivation

Reliability solves the problem of keeping a system correct and useful over time despite failures.

Where it fits

Reliability is a non-functional requirement and a system design concern. It connects availability, redundancy, failover, monitoring, incident response, and testing.

Mental model

Reliable systems assume components will fail and are designed to continue operating, recover quickly, or fail safely.

Common mistakes

Confusing reliability with availability.
Measuring reliability only after incidents.
Designing happy paths without failure paths.