Merge pull request #2865 from mattbostock/add_marathon_port_ordinal_label

Marathon SD: Set port index label

discovery/marathon/marathon.go

@@ -20,6 +20,7 @@ import (
 	"math/rand"
 	"net"
 	"net/http"
+	"strconv"
 	"strings"
 	"time"
 
@@ -43,6 +44,9 @@ const (
 	appLabel model.LabelName = metaLabelPrefix + "app"
 	// imageLabel is the label that is used for the docker image running the service.
 	imageLabel model.LabelName = metaLabelPrefix + "image"
+	// portIndexLabel is the integer port index when multiple ports are defined;
+	// e.g. PORT1 would have a value of '1'
+	portIndexLabel model.LabelName = metaLabelPrefix + "port_index"
 	// taskLabel contains the mesos task name of the app instance.
 	taskLabel model.LabelName = metaLabelPrefix + "task"
 
@@ -323,6 +327,7 @@ func targetsForApp(app *App) []model.LabelSet {
 			target := model.LabelSet{
 				model.AddressLabel: model.LabelValue(targetAddress),
 				taskLabel:          model.LabelValue(t.ID),
+				portIndexLabel:     model.LabelValue(strconv.Itoa(i)),
 			}
 			if i < len(app.PortDefinitions) {
 				for ln, lv := range app.PortDefinitions[i].Labels {