Debugging Dubbo‑Spring Cloud Integration with Arthas: Solving Mixed Protocol Issues

Usage Background

In a large team, different projects use different RPC frameworks: an older project uses Dubbo with the Dubbo protocol, while a newer project uses Spring Cloud’s Feign client with HTTP. This creates two problems: the Dubbo service must support both Dubbo and HTTP protocols, and Feign clients must call the Dubbo service’s HTTP endpoint without losing dynamic service discovery or load‑balancing capabilities.

Solution Idea

The first problem is straightforward because Dubbo already provides an HTTP protocol exposure; configuring Dubbo to expose both protocols solves it. The second problem is trickier: Dubbo registers with Zookeeper, while Spring Cloud uses Eureka. Feign can call any HTTP interface, but it lacks built‑in load‑balancing and failover for the Dubbo‑exposed HTTP endpoint. The proposed approach is to register Dubbo services in Eureka so that Feign can invoke them losslessly.

To achieve this, the Dubbo project adds an SPI Container extension that registers the service with Eureka. The custom container class is defined as follows:

class EurekaDubboContainer implements Container { ... }

The container must be declared in META‑INF/dubbo/org.apache.dubbo.container.Container, e.g.

META-INF/dubbo/org.apache.dubbo.container.Container: spring=com.xxx.EurekaDubboContainer

Arthas in Action

After adding the container and restarting, the service starts without errors, but Feign still cannot call it. Using Arthas, the author inspected the Dubbo extension loading process. The investigation revealed that the custom container class was loaded (verified with sc -d *.EurekaDubboContainer and jad *.EurekaDubboContainer), but it was not present in Dubbo’s ExtensionLoader cached instances. Further Ognl queries showed the container was missing from the cached instances and listed in the loader’s exceptions, indicating a duplicate key in META‑INF.

Correcting the duplicate key resolved the loading issue, allowing the Dubbo service to register with Eureka and be called by Feign without loss.

Conclusion

The experience shows that seemingly unsolvable integration problems can be addressed by extending Dubbo’s SPI mechanism and using Arthas for deep runtime inspection. By registering Dubbo services in Eureka, both protocols coexist, and Feign clients gain proper load‑balancing and failover. The article encourages developers to explore Arthas’s Ognl capabilities for diagnosing hidden extension loading problems.