SLA notes: what an uptime promise actually costs
For co-ops considering SLAs, the honest math: promising 99.9% costs 10x more checking than 99% (the last nine costs exponentially), and 'alert within a minute' requires polling faster than the failure can hide. My ledger now includes MTTA (time-to-alert) alongside uptime: current median 47 seconds. Publish your monitoring costs or you are selling vibes.