Kas saaksite selgitada Circuit Breaker mustri tööpõhimõtet ja selle rolli süsteemi usaldusväärsuse tagamisel?

The Circuit Breaker pattern is used to increase the reliability of distributed systems by preventing repeated calls to a failing or slow-responding service.

How it works:

1. Closed (closed state): All requests pass as usual.
2. Open (open state): If the error count exceeds a threshold, the Circuit Breaker «opens» — new requests immediately receive an error without attempting to call the service.
3. Half-Open (half-open state): After some time, the Circuit Breaker allows a limited number of requests to check if the service has recovered.

If requests succeed, the state returns to Closed; otherwise, it goes back to Open.

This prevents overload on a non-functioning service and allows the system to recover faster.

Example usage in Go (simplified):

// Pseudo-code
cb := NewCircuitBreaker()

if cb.AllowRequest() {
    err := callRemoteService()
    if err != nil {
        cb.RecordFailure()
    } else {
        cb.RecordSuccess()
    }
} else {
    // Return error immediately without calling the service
}

Thus, the Circuit Breaker helps make the system more resilient to failures.