# Calculating composite SLA

- **期号**: SRE Weekly Issue #308（2022-02-06）
- **作者**: Alex Ewerlöf
- **链接**: https://alexewerlof.medium.com/calculating-composite-sla-d855eaf2c655

## 简介

How do complex service dependencies affect your SLA?  What if service A depends on service B and C being up, but service D or E being up?

> TLDR; for serial, multiply availability; For parallels, multiply unavailability.

## 正文

> ⚠️ 抓取失败：HTTP 403