Follow up on PR 2868 (#2877)

This fix is a follow up on comment https://github.com/coredns/coredns/pull/2868#discussion_r291609761Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

go.mod

@@ -4,7 +4,6 @@ go 1.12
 
 require (
 	cloud.google.com/go v0.39.0 // indirect
-	github.com/DataDog/dd-trace-go v1.14.0
 	github.com/Shopify/sarama v1.21.0 // indirect
 	github.com/apache/thrift v0.12.0 // indirect
 	github.com/aws/aws-sdk-go v1.19.41
@@ -68,7 +67,6 @@ require (
 	google.golang.org/appengine v1.6.0 // indirect
 	google.golang.org/genproto v0.0.0-20190530194941-fb225487d101 // indirect
 	google.golang.org/grpc v1.21.0
-	gopkg.in/DataDog/dd-trace-go.v0 v0.6.1
 	gopkg.in/DataDog/dd-trace-go.v1 v1.14.0
 	gopkg.in/inf.v0 v0.9.1 // indirect
 	k8s.io/api v0.0.0-20190313235455-40a48860b5ab

plugin/trace/trace.go

@@ -54,7 +54,8 @@ func (t *trace) OnStartup() error {
 		case "zipkin":
 			err = t.setupZipkin()
 		case "datadog":
-			t.setupDatadog()
+			tracer := opentracer.New(tracer.WithAgentAddr(t.Endpoint), tracer.WithServiceName(t.serviceName), tracer.WithDebugMode(true))
+			t.tracer = tracer
 		default:
 			err = fmt.Errorf("unknown endpoint type: %s", t.EndpointType)
 		}
@@ -75,11 +76,6 @@ func (t *trace) setupZipkin() error {
 	return err
 }
 
-func (t *trace) setupDatadog() {
-	tracer := opentracer.New(tracer.WithAgentAddr(t.Endpoint), tracer.WithServiceName(t.serviceName), tracer.WithDebugMode(true))
-	t.tracer = tracer
-}
-
 // Name implements the Handler interface.
 func (t *trace) Name() string { return "trace" }