No breaker vs circuit breaker
Without a breaker, every call waits for the failed payment API, and the waiting calls pile up. A circuit breaker opens after repeated failures and fails calls at once during a cooldown. In a 15 s outage, p99 is 6,784 ms without a breaker and 544 ms with one. Both lose about 29 percent of checkouts.
3 of 3 up · availability 99.9999%
Case 1
The payment API is down from 0:20 to 0:35. Shoppers tap Pay again, so checkout traffic doubles from 120 to 240 requests/s. p99 must stay below 700 ms and availability at 65 percent or more.
| Measure | Goal | No circuit breaker | Circuit breaker, 5 s cooldown |
|---|---|---|---|
| p99 latency | under 700 ms | 6.8 s Fail | 544 ms Pass |
| Availability | at least 65% | 71.4% Pass | 70.9% Pass |
| Monthly cost | 8 USD/mo | 12 USD/mo | |
| Error rate | 28.6% | 29.1% |