plugin/metrics: add 'server' label (#1682)

* plugin/metrics: add 'server' label

This uses the new WithServer(ctx) to get the current server from the
context.

First in a larger refactor to make all plugins do this.

* compile

* compile

* lala test

* compile and test

* typos

* Dont duplicate the code

1 files changed, 22 insertions, 10 deletions

diff --git a/plugin/metrics/vars/report.go b/plugin/metrics/vars/report.go
index 568a291e3..dc597c610 100644
--- a/plugin/metrics/vars/report.go
+++ b/plugin/metrics/vars/report.go
@@ -3,13 +3,15 @@ package vars
 import (
 	"time"
 
+	"github.com/coredns/coredns/plugin"
 	"github.com/coredns/coredns/request"
 
 	"github.com/miekg/dns"
+	"golang.org/x/net/context"
 )
 
 // Report reports the metrics data associcated with request.
-func Report(req request.Request, zone, rcode string, size int, start time.Time) {
+func Report(ctx context.Context, req request.Request, zone, rcode string, size int, start time.Time) {
 	// Proto and Family.
 	net := req.Proto()
 	fam := "1"
@@ -17,25 +19,35 @@ func Report(req request.Request, zone, rcode string, size int, start time.Time)
 		fam = "2"
 	}
 
-	typ := req.QType()
+	server := WithServer(ctx)
 
-	RequestCount.WithLabelValues(zone, net, fam).Inc()
-	RequestDuration.WithLabelValues(zone).Observe(time.Since(start).Seconds())
+	typ := req.QType()
+	RequestCount.WithLabelValues(server, zone, net, fam).Inc()
+	RequestDuration.WithLabelValues(server, zone).Observe(time.Since(start).Seconds())
 
 	if req.Do() {
-		RequestDo.WithLabelValues(zone).Inc()
+		RequestDo.WithLabelValues(server, zone).Inc()
 	}
 
 	if _, known := monitorType[typ]; known {
-		RequestType.WithLabelValues(zone, dns.Type(typ).String()).Inc()
+		RequestType.WithLabelValues(server, zone, dns.Type(typ).String()).Inc()
 	} else {
-		RequestType.WithLabelValues(zone, other).Inc()
+		RequestType.WithLabelValues(server, zone, other).Inc()
 	}
 
-	ResponseSize.WithLabelValues(zone, net).Observe(float64(size))
-	RequestSize.WithLabelValues(zone, net).Observe(float64(req.Len()))
+	ResponseSize.WithLabelValues(server, zone, net).Observe(float64(size))
+	RequestSize.WithLabelValues(server, zone, net).Observe(float64(req.Len()))
 
-	ResponseRcode.WithLabelValues(zone, rcode).Inc()
+	ResponseRcode.WithLabelValues(server, zone, rcode).Inc()
+}
+
+// WithServer returns the current server handling the request.
+func WithServer(ctx context.Context) string {
+	srv := ctx.Value(plugin.ServerCtx{})
+	if srv == nil {
+		return ""
+	}
+	return srv.(string)
 }
 
 var monitorType = map[uint16]bool{