System Reliability: MTBF and MTTR

### Reliability vs Availability

While Availability is about uptime, Reliability is about the probability that the system will function correctly under specific conditions. A system can be highly available but unreliable if it constantly returns errors while remaining online.

### Core Metrics

1. **MTBF (Mean Time Between Failures):** The average time a system operates before breaking down. Higher is better. 2. **MTTR (Mean Time To Recovery):** The average time it takes to restore a system after a failure. Lower is better.

### Improving Reliability

To improve these metrics, engineers rely on robust monitoring, automated alerting, comprehensive runbooks, and chaos engineering practices to uncover weaknesses before they cause real outages.