# Circuit Breakers & Retries — System Design

Source: https://www.geekswithgeeks.com/en/system-design/sd-circuit-breaker

> Failing fast and isolating trouble instead of cascading it.

## The cascading failure problem

When a downstream service slows down, callers pile up waiting threads/connections, which slows them down too — the failure cascades upstream and can take down the whole system.

## A circuit breaker in your house

Like an electrical breaker, a **circuit breaker** pattern trips **open** after repeated failures — it stops calling the failing service immediately (fast failure instead of a hanging timeout), waits, then tries a trickle of test calls (**half-open**) before closing again.

## Retry with backoff

Blind immediate retries make an overloaded service worse. Back off exponentially and add jitter so retries don't all land at once.

```text
delay = base * 2^attempt + random_jitter
if attempt > max_attempts: give up, fallback
else: sleep(delay); retry
```

Output:

```
Prevents retry storms from making an outage worse
```

## Bulkheads and graceful degradation

**Bulkheads** give each dependency its own thread pool/connection limit so one slow dependency can't starve requests to others — like a ship's watertight compartments. When a non-critical dependency is down, degrade gracefully: show cached recommendations instead of failing the whole page.