plugin/trace - Use compatible tag name for datadog (#4408)

Traces are currently working properly with datadog with the exception of having the ability to facet the tags

![image](https://user-images.githubusercontent.com/5513509/105051238-dddbbd00-5a6e-11eb-8fb2-071b3b1fa8cc.png)

In order to get valuable graph in dashboard the tag on the metrics need to be faceted by datadog.
This PR update the tags with facetable path.
While keeping backward compatibility with existing path for zipkin.

Graph like:
![image](https://user-images.githubusercontent.com/5513509/93375960-339e1f80-f859-11ea-81f0-a1074c375630.png)
![image](https://user-images.githubusercontent.com/5513509/93375997-4153a500-f859-11ea-9f8d-63d45217c681.png)
![image](https://user-images.githubusercontent.com/5513509/93376064-5597a200-f859-11ea-823a-6768f59e3497.png)
![image](https://user-images.githubusercontent.com/5513509/93376405-d6ef3480-f859-11ea-8d6f-58dda247cc86.png)
![image](https://user-images.githubusercontent.com/5513509/93376518-069e3c80-f85a-11ea-9a7e-0426a3817439.png)

Signed-off-by: bob <bob.bouteillier@datadoghq.com>

2 files changed, 51 insertions, 21 deletions

diff --git a/plugin/trace/trace.go b/plugin/trace/trace.go
index bbca68849..c1b0fb4cf 100644
--- a/plugin/trace/trace.go
+++ b/plugin/trace/trace.go
@@ -25,14 +25,34 @@ import (
 )
 
 const (
-	tagName                 = "coredns.io/name"
-	tagType                 = "coredns.io/type"
-	tagRcode                = "coredns.io/rcode"
-	tagProto                = "coredns.io/proto"
-	tagRemote               = "coredns.io/remote"
 	defaultTopLevelSpanName = "servedns"
 )
 
+type traceTags struct {
+	Name   string
+	Type   string
+	Rcode  string
+	Proto  string
+	Remote string
+}
+
+var tagByProvider = map[string]traceTags{
+	"default": {
+		Name:   "coredns.io/name",
+		Type:   "coredns.io/type",
+		Rcode:  "coredns.io/rcode",
+		Proto:  "coredns.io/proto",
+		Remote: "coredns.io/remote",
+	},
+	"datadog": {
+		Name:   "coredns.io@name",
+		Type:   "coredns.io@type",
+		Rcode:  "coredns.io@rcode",
+		Proto:  "coredns.io@proto",
+		Remote: "coredns.io@remote",
+	},
+}
+
 type trace struct {
 	count uint64 // as per Go spec, needs to be first element in a struct
 
@@ -46,6 +66,7 @@ type trace struct {
 	every                uint64
 	datadogAnalyticsRate float64
 	Once                 sync.Once
+	tagSet               traceTags
 }
 
 func (t *trace) Tracer() ot.Tracer {
@@ -68,6 +89,7 @@ func (t *trace) OnStartup() error {
 				tracer.WithAnalyticsRate(t.datadogAnalyticsRate),
 			)
 			t.tracer = tracer
+			t.tagSet = tagByProvider["datadog"]
 		default:
 			err = fmt.Errorf("unknown endpoint type: %s", t.EndpointType)
 		}
@@ -90,6 +112,8 @@ func (t *trace) setupZipkin() error {
 		return err
 	}
 	t.tracer = zipkinot.Wrap(tracer)
+
+	t.tagSet = tagByProvider["default"]
 	return err
 }
 
@@ -119,11 +143,11 @@ func (t *trace) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
 	ctx = ot.ContextWithSpan(ctx, span)
 	status, err := plugin.NextOrFailure(t.Name(), t.Next, ctx, rw, r)
 
-	span.SetTag(tagName, req.Name())
-	span.SetTag(tagType, req.Type())
-	span.SetTag(tagProto, req.Proto())
-	span.SetTag(tagRemote, req.IP())
-	span.SetTag(tagRcode, rcode.ToString(rw.Rcode))
+	span.SetTag(t.tagSet.Name, req.Name())
+	span.SetTag(t.tagSet.Type, req.Type())
+	span.SetTag(t.tagSet.Proto, req.Proto())
+	span.SetTag(t.tagSet.Remote, req.IP())
+	span.SetTag(t.tagSet.Rcode, rcode.ToString(rw.Rcode))
 
 	return status, err
 }
diff --git a/plugin/trace/trace_test.go b/plugin/trace/trace_test.go
index 613f88b6d..832447138 100644
--- a/plugin/trace/trace_test.go
+++ b/plugin/trace/trace_test.go
@@ -28,6 +28,11 @@ func TestStartup(t *testing.T) {
 		t.Errorf("Error starting tracing plugin: %s", err)
 		return
 	}
+
+	if m.tagSet != tagByProvider["default"] {
+		t.Errorf("TagSet by proviser hasn't been corectly initialized")
+	}
+
 	if m.Tracer() == nil {
 		t.Errorf("Error, no tracer created")
 	}
@@ -51,7 +56,7 @@ func TestTrace(t *testing.T) {
 			question: new(dns.Msg).SetQuestion("example.net.", dns.TypeCNAME),
 		},
 	}
-
+	defaultTagSet := tagByProvider["default"]
 	for _, tc := range cases {
 		t.Run(tc.name, func(t *testing.T) {
 			w := dnstest.NewRecorder(&test.ResponseWriter{})
@@ -65,6 +70,7 @@ func TestTrace(t *testing.T) {
 				}),
 				every:  1,
 				tracer: m,
+				tagSet: defaultTagSet,
 			}
 			ctx := context.TODO()
 			if _, err := tr.ServeDNS(ctx, w, tc.question); err != nil {
@@ -83,20 +89,20 @@ func TestTrace(t *testing.T) {
 				t.Errorf("Unexpected span name: rootSpan.Name: want %v, got %v", defaultTopLevelSpanName, rootSpan.OperationName)
 			}
 
-			if rootSpan.Tag(tagName) != req.Name() {
-				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", tagName, req.Name(), rootSpan.Tag(tagName))
+			if rootSpan.Tag(defaultTagSet.Name) != req.Name() {
+				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", defaultTagSet.Name, req.Name(), rootSpan.Tag(defaultTagSet.Name))
 			}
-			if rootSpan.Tag(tagType) != req.Type() {
-				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", tagType, req.Type(), rootSpan.Tag(tagType))
+			if rootSpan.Tag(defaultTagSet.Type) != req.Type() {
+				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", defaultTagSet.Type, req.Type(), rootSpan.Tag(defaultTagSet.Type))
 			}
-			if rootSpan.Tag(tagProto) != req.Proto() {
-				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", tagProto, req.Proto(), rootSpan.Tag(tagProto))
+			if rootSpan.Tag(defaultTagSet.Proto) != req.Proto() {
+				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", defaultTagSet.Proto, req.Proto(), rootSpan.Tag(defaultTagSet.Proto))
 			}
-			if rootSpan.Tag(tagRemote) != req.IP() {
-				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", tagRemote, req.IP(), rootSpan.Tag(tagRemote))
+			if rootSpan.Tag(defaultTagSet.Remote) != req.IP() {
+				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", defaultTagSet.Remote, req.IP(), rootSpan.Tag(defaultTagSet.Remote))
 			}
-			if rootSpan.Tag(tagRcode) != rcode.ToString(tc.rcode) {
-				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", tagRcode, rcode.ToString(tc.rcode), rootSpan.Tag(tagRcode))
+			if rootSpan.Tag(defaultTagSet.Rcode) != rcode.ToString(tc.rcode) {
+				t.Errorf("Unexpected span tag: rootSpan.Tag(%v): want %v, got %v", defaultTagSet.Rcode, rcode.ToString(tc.rcode), rootSpan.Tag(defaultTagSet.Rcode))
 			}
 		})
 	}