1 min lesson
Reliability: SLOs, error budgets, observability
Use "Reliability: SLOs, error budgets, observability" to explain each part and the role it plays.
Step 1 of 2
Everything in this module - the edge, the limits, the regions, the budgets - should hang off one number: the SLO. It turns "is this reliable enough?" from a vibe into a decision you can defend.
An SLI is what you measure, an SLO is the target you commit to and the error budget is the allowed shortfall. The budget is the lever: spend it on shipping when you're healthy, freeze and stabilize when you've burned it.
- SLI
- A measured ratio of good events to total - e.g. fraction of requests under 300 ms or fraction returning non-5xx.
- SLO
- The target on that SLI - e.g. 99.9% of requests succeed over 28 days.
- Error budget
- 100% minus the SLO - 0.1% here, about 40 min/month of allowed failure. It's a budget you're meant to spend, not hoard.
The cultural payoff fits Cursor's bias to ship: a healthy error budget is permission to move fast and take risks. A burned budget is the signal to slow down and harden. The number, not opinion, arbitrates the ship-versus-stabilize fight.