Availability

Cards

1. A service promises 99.99% availability. How much downtime does that allow in a year? easy Estimate
2. How much recent data you can afford to lose in a disaster, measured in time, is the _____. How long you can afford to be down is the _____. easy Fill in the blank
3. A service promises 99.9% availability. How much downtime does that allow in a 30-day month? easy Estimate
4. Active-active versus active-passive across two sites: what does each cost? medium Flashcard
5. A request passes through two components in a row, each 99.9% available. What is the availability of the whole path? medium Multiple choice
6. Your service calls a provider that is only 99% available. How can your service be more available than it? medium Flashcard
7. The math said two replicas give about 99.9999%, but both went down together. Which assumption broke? medium Multiple choice
8. A service has a 99.95% success-rate SLO over 30 days and serves 1 million requests a day. How many failed requests can it afford in that period? medium Estimate
9. Many outages start with a change. How do you limit the damage of a bad deploy? medium Flashcard
10. Peak load needs 6 servers. They are spread evenly over 3 availability zones, and the service must survive losing a whole zone. How many servers do you run? medium Multiple choice
11. Which setup loses no acknowledged writes if the database's availability zone is destroyed? medium Multiple choice
12. What is a cell-based architecture, and what does it buy? hard Flashcard
13. Should a load balancer's health check also check the database? What can go wrong? hard Flashcard
14. Three independent replicas are each 95% available, and the service is up while any one of them is. How many minutes a month (30 days) is it down? hard Estimate