Real World Example

UPI and card providers in India sometimes have partial outages during peak hours. Payment platforms (Razorpay, PhonePe, Paytm) and the shops using them protect themselves so that checkout fails gracefully, and the rest of the app (search, product pages, cart) keeps working. Netflix popularised these patterns with Hystrix; Resilience4j is the modern Java version.

user clicks Pay
   -> order-service.charge()
        Bulkhead(max 10 concurrent)   -- full? -> "payment pending"
        CircuitBreaker(paymentService) -- open? -> "payment pending"
        Retry(2x on timeout, same Idempotency-Key)
        -> payment-service -> bank / UPI provider
 meanwhile: search, product pages, cart  -> unaffected (other threads, other breakers)

@Service
@RequiredArgsConstructor
@Slf4j
public class PaymentGateway {

    private final PaymentClient paymentClient;
    private final OrderRepository orders;

    @Retry(name = "paymentService")
    @CircuitBreaker(name = "paymentService", fallbackMethod = "markPending")
    @Bulkhead(name = "paymentService")
    public PaymentResult charge(Order order) {
        PaymentResponse res = paymentClient.charge(
                "order-" + order.getId(),                  // same key on every retry
                new ChargeRequest(order.getId(), order.getTotal(), order.getPaymentMode()));
        return PaymentResult.paid(res.paymentId());
    }

    PaymentResult markPending(Order order, Throwable ex) {
        log.warn("Payment for order {} pending: {}", order.getId(), ex.getClass().getSimpleName());
        order.markPaymentPending();
        orders.save(order);
        return PaymentResult.pending();   // a scheduled job / webhook confirms later
    }
}

curl -X POST localhost:8080/api/orders -H "Authorization: Bearer $TOKEN" -H "Content-Type: application/json" \
  -d '{"userId": 42, "productId": 7, "quantity": 1, "paymentMode": "UPI"}'

HTTP/1.1 202 Accepted
{"orderId":1007,"status":"PAYMENT_PENDING","message":"We are confirming your payment. You will get an SMS in a few minutes."}

$ curl -s localhost:8082/actuator/health | jq .components.circuitBreakers
{"status":"UNKNOWN","details":{"paymentService":{"status":"CIRCUIT_OPEN",
 "details":{"failureRate":"70.0%","state":"OPEN","notPermittedCalls":42}}}}