refactor: Replace OpenFeign service calls with Dubbo RPC (Spring Cloud Alibaba + Nacos integration)

[dennis9486]

Title

Replace OpenFeign service calls with Dubbo RPC (Spring Cloud Alibaba + Nacos integration)

Summary

Migrate existing inter-service calls that use OpenFeign to Dubbo RPC and use Nacos for service discovery/configuration. Goals: reduce network overhead, improve high-concurrency performance, and unify governance (services expose/reference interfaces via Dubbo).

Requirements (key points)

• Use Dubbo (recommend 3.x) for service exposure and consumption, with Nacos as the registry (keep Spring Cloud Alibaba environment).
• Preserve existing interface contracts (Java interfaces + DTOs) and aim for a non-invasive replacement.
• Provide timeout, retry, rate-limit and fallback strategies (can integrate Dubbo with Sentinel).
• Add unit/integration/contract tests to ensure behavioral parity.
• Provide a rollback plan: allow Feign and Dubbo to run in parallel temporarily to enable staged (canary) switch-over.

Tasks

• [ ] Add shared Dubbo config in platform/common (Nacos registry, protocol, serialization, metadata-report).
• [ ] Expose provider services as Dubbo providers (annotations/config) and register to Nacos.
• [ ] Replace Feign clients with Dubbo references on the consumer side (keep same Java interfaces where possible).
• [ ] Add circuit-breaker / rate-limiting / fallback strategies (recommend integrating Sentinel) and wire up monitoring metrics.
• [ ] Implement integration tests: provider/consumer local e2e, contract tests, timeout/retry/fallback scenarios.
• [ ] Update docs: developer onboarding, config reference, FAQ and rollback steps.

Acceptance Criteria

• Key service calls after migration behave the same (API semantics, exception behavior, timeout/retry policies).
• Nacos shows Dubbo service instances and service discovery works reliably.
• Performance/resource usage meets or improves upon Feign-based implementation.

Migration steps (brief)

1. Prepare shared Dubbo config and publish it to config-center (Nacos).
2. Enable Dubbo providers on target services while keeping Feign endpoints active; register providers to Nacos for canary.
3. Switch some consumers to Dubbo invocation and validate in parallel (or route small percentage of traffic via gateway).
4. Monitor errors, latency, QPS; expand canary after validation.
5. Once stable, remove Feign code and fully switch to Dubbo.

Notes / Caveats

• Ensure DTOs are serializable and pick a compatible serialization (protobuf / fastjson2 / hessian2, etc.) per team standard.
• Maintain class/interface compatibility between consumer and provider versions.
• Evaluate gateway and cross-language scenarios (if non-Java clients exist, consider compatibility layer).
• Keep authentication/authorization controls at Dubbo layer or at gateway as required.