# The Calculus of Service Availability

- **期号**: SRE Weekly Issue #73（2017-05-21）
- **作者**: —
- **链接**: http://queue.acm.org/detail.cfm?id=3096459

## 简介

As the title suggest, this ACM Queue article goes into some depth on the kinds of calculations one might make when designing a reliable system. Specifically, they focus on service dependencies and introduce Google’s “rule of the extra 9”: a dependency should have one more nine of reliability than the thing that critically depends on it.

## 正文

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