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
Every decision in this module, from the edge and the limits to the regions and 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, such as the fraction of requests under 300 ms or the fraction returning non-5xx.
- SLO
- The target on that SLI, for example 99.9% of requests succeed over 28 days.
- Error budget
- 100% minus the SLO: 0.1% here, about 40 min/month of allowed failure. You're meant to spend it on shipping.
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 budget number settles the ship-versus-stabilize fight.