feat(metrics): improve graphite settings

Fixes the broken support for overriding settings with ENV variables.
closes #5769

pkg/metrics/graphite.go

@@ -24,10 +24,15 @@ func CreateGraphitePublisher() (*GraphitePublisher, error) {
 		return nil, nil
 	}
 
+	address := graphiteSection.Key("address").String()
+	if address == "" {
+		return nil, nil
+	}
+
 	publisher := &GraphitePublisher{}
 	publisher.prevCounts = make(map[string]int64)
 	publisher.protocol = "tcp"
-	publisher.address = graphiteSection.Key("address").MustString("localhost:2003")
+	publisher.address = address
 
 	safeInstanceName := strings.Replace(setting.InstanceName, ".", "_", -1)
 	prefix := graphiteSection.Key("prefix").Value()

pkg/metrics/graphite_test.go

@@ -34,6 +34,29 @@ func TestGraphitePublisher(t *testing.T) {
 		So(publisher.address, ShouldEqual, "localhost:2001")
 	})
 
+	Convey("Test graphite publisher default prefix", t, func() {
+		var err error
+		err = setting.NewConfigContext(&setting.CommandLineArgs{
+			HomePath: "../../",
+		})
+
+		So(err, ShouldBeNil)
+
+		sec, err := setting.Cfg.NewSection("metrics.graphite")
+		sec.NewKey("address", "localhost:2001")
+
+		So(err, ShouldBeNil)
+
+		setting.InstanceName = "hostname.with.dots.com"
+		publisher, err := CreateGraphitePublisher()
+
+		So(err, ShouldBeNil)
+		So(publisher, ShouldNotBeNil)
+
+		So(publisher.prefix, ShouldEqual, "service.grafana.hostname_with_dots_com.")
+		So(publisher.address, ShouldEqual, "localhost:2001")
+	})
+
 	Convey("Test graphite publisher default values", t, func() {
 		var err error
 		err = setting.NewConfigContext(&setting.CommandLineArgs{
@@ -48,9 +71,6 @@ func TestGraphitePublisher(t *testing.T) {
 		publisher, err := CreateGraphitePublisher()
 
 		So(err, ShouldBeNil)
-		So(publisher, ShouldNotBeNil)
-
-		So(publisher.prefix, ShouldEqual, "service.grafana.hostname_with_dots_com.")
-		So(publisher.address, ShouldEqual, "localhost:2003")
+		So(publisher, ShouldBeNil)
 	})
 }