Sleuth + Zipkin 分布式链路追踪

@RestController
@Slf4j
public class OrderController {
    @Autowired
    private RestTemplate restTemplate;

    @GetMapping("/order/{orderId}")
    public Order getOrder(@PathVariable String orderId) {
        // Trace ID 自动注入 MDC，日志自动携带
        log.info("查询订单：orderId={}", orderId);

        // 调用库存服务（Trace 自动传播）
        StockDTO stock = restTemplate.getForObject(
            "http://FEIXIANG-INVENTORY-SERVICE/inventory/" + orderId,
            StockDTO.class
        );

        // 调用支付服务（Trace 自动传播）
        PaymentDTO payment = restTemplate.getForObject(
            "http://FEIXIANG-PAYMENT-SERVICE/payment/" + orderId,
            PaymentDTO.class
        );

        return Order.builder()
                .orderId(orderId)
                .stock(stock)
                .payment(payment)
                .build();
    }
}

@RestController
public class OrderController {
    @Autowired
    private ObservationRegistry observationRegistry;

    @GetMapping("/order/create")
    public Order createOrder(@RequestBody OrderRequest request) {
        // 创建自定义 Span 记录业务操作
        return Observation.createNotStarted("order.create-business-logic", observationRegistry)
                .lowCardinalityKeyValue("order.type", request.getType())
                .observe(() -> {
                    // 业务逻辑
                    Order order = orderService.create(request);
                    log.info("订单创建成功：orderId={}", order.getId());
                    return order;
                });
    }
}

// ❌ 错误：异步线程中 Trace ID 丢失
@Async
public void sendNotification(String orderId) {
    log.info("发送通知");  // MDC 中没有 Trace ID
}

// ✅ 正确：使用 Context Propagation
@Async
public void sendNotification(String orderId) {
    try (var scope = observationRegistry.getCurrentObservation().openScope()) {
        log.info("发送通知");  // MDC 中有 Trace ID
    }
}