Availability math
On This Lesson 4 topics
This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.
In this lesson
compute availability of systems from their parts.
Planned topics
- Serial dependencies multiply: two 99.9% services in series give about 99.8%.
- Parallel redundancy improves: 1 - (1-a)^n assuming independent failures.
- Independence is rarely true; shared causes (deploys, config, region) break the math.
- Convert to downtime: 99.95% is about 22 minutes per month; verify figure before recording.
Draft outline details
Demonstration
a worked calculation: checkout depends on identity (99.95%), orders DB (99.99%), payments (99.9%), FulfillCo stock API (99.9%); product of those; then add a cache fallback.
Check your understanding
What is the availability of two 99.9% services in series?
Show answer
About 99.8%.
Practice
Apply this lesson with the module's lab, exercises and quiz.
Marking a lesson complete is optional and you can undo it any time. Your progress stays in this browser.