Platform & DevOps·Running it: capacity, failure and recovery
you run at sixty percent so a zone failure or a traffic spike does not immediately become an outage.
Headroom
Also calledcapacity headroom, spare capacity, buffer
Deliberate unused capacity held to absorb failures, spikes and the time it takes to add more. The right amount is set by what you must survive without scaling — commonly the loss of one zone — plus however long provisioning actually takes. It is the least glamorous line on a cloud bill and the first thing cut in a cost exercise, usually by someone who has not connected it to the last incident.