core practice · system design prompt
Design exercise: Reliability & Fault Tolerance
SLOs, error budgets, redundancy, graceful degradation, overload control, and failure-domain design. Implement designOutline() returning non-empty values for: slo, failureDomain, degradationMode. Each value must name a concrete mechanism or decision.
The mechanism
Reliability is a measurable product property. Define an SLO, budget failure, isolate fault domains, shed optional work, and test recovery before incidents. Scope: this card owns the target-setting layer — deciding what 'reliable enough' means and budgeting for it with SLOs, error budgets and fault domains. Staying CORRECT while a request is failing is `distributed-failure-recovery`; the concrete queue-retry mechanism is `retries-dlq`.
Expected evidence
A design outline with slo, failureDomain, degradationMode plus an explicit failure mode or trade-off.
Try this drill in the practice workspace →
Hints when you need them
- Name the failure mode before selecting the mechanism.