TinkerNo run yet.
Round robin over four servers, before the sale.Ash 0 waiting · Birch 0 waiting · Cedar 0 waiting · Dogwood 0 waiting
Chapter 4 of 7
Is it alive?
As the sale starts, Cedar crashes. The balancer can’t tell: it keeps giving Cedar its turn, and those customers wait for nothing.
This chapter: How does a balancer find a dead server, and what can it miss?
About this chapter
You will learn
- A health check asks every server, on a timer, whether it answers
- A server is pulled after a number of misses in a row
- Why a slow server that still answers passes
Words you’ll meet
- Health check
- A small request the balancer sends each server on a timer, to see if it answers in time.
- Pulled
- Taken out of rotation: the balancer stops sending it requests.
- Gray failure
- A server that is broken for customers but still passes its health check.
Step 1 of 6
Cedar is down from one second in, and the balancer keeps sending it every fourth request.
Run the sale.