James C.J Chung

@DavidLiu506 Does this PR passes all three neighbor testcases? Scenario#4, Scenario#4.5 and Scenario#5?

**Temporary Solution:** For temporary solution in Subnet Manager, we can modify codes in `SubnetController.java` line 543 to: ``` ... import org.springframework.web.client.HttpClientErrorException; ... // TODO: delete gateway port in port manager....

Subnet's routing table also has similar issue. We need to try and catch `this.subnetService.deleteSubnetRoutingRuleInRM(projectId, subnetId);` too: ``` // delete subnet routing rule in route manager try { this.subnetService.deleteSubnetRoutingRuleInRM(projectId, subnetId); }...

The error log from PM: ``` Content-Type: application/json Accept: */* User-Agent: Java/11.0.8 Host: portmanager-service.default.svc.cluster.local:9006 Connection: keep-alive Content-Length: 188 {"vpc_id":null,"subnet_id":"ca1e31f2-5ed1-4b68-af86-8e2d4187ebc5","operation_type":"add","gateway_port_ids":["8e162a59-7e52-4966-b323-8bd7756b1387","1f34d7e8-2781-4487-b832-4541e2d1b4ac"]}] 2021-04-08 22:01:20.427 DEBUG 1 --- [nio-8080-exec-6] o.apache.catalina.valves.RemoteIpValve : Incoming request /project/bba04015f47b4719a8edc8006e0abb27/update-l3-neighbors...

@chenpiaoping add this annotation before the method. ``` @JsonInclude(JsonInclude.Include.NON_ABSENT) ``` @kevin-zhonghao, maybe we can try this in the subnet entity.

Zipkin vs. Jaeger: https://epsagon.com/observability/zipkin-or-jaeger-the-best-open-source-tools-for-distributed-tracing/