Stage 1 · Lesson 5 of 7
SLOs and error budgets
A , or SLO, is a reliability target measured from the user's side. For example: 99.9 percent of requests succeed within 300ms over 30 days. The error budget is the failure that target still allows.
At 99.9 percent that is about 43 minutes of full a month. While budget remains, teams ship freely. Once it is spent, they slow down and fix reliability.
Across teams, this replaces arguments about "reliable enough" with a shared number. It also lets you ask whether a 's SLO can support yours.
Common trapsetting 99.99 percent everywhere: each extra nine costs far more effort, and a service cannot be more reliable than the dependencies it calls in series, one after another.
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Resources for this stage
Start with· follow one of these
- CoursePaidSystem Design Patterns: From Fundamentals to Real Systems
Design Gurus · Intermediate · Subscription
The distributed patterns behind most designs, to judge proposals from other teams
- GuideFreeMartin Fowler's Website
Martin Fowler · Intermediate
Free, clear writing on architecture styles, microservices and evolving designs