Extend marathon port discovery to allow port names as identifier

docs/content/user-guides/marathon.md

@@ -14,13 +14,21 @@ Traefik tries to detect the configured mode and route traffic to the right IP ad
 
 ## Port detection
 
-Traefik also attempts to determine the right port (which is a [non-trivial matter in Marathon](https://mesosphere.github.io/marathon/docs/ports.html)).
-Following is the order by which Traefik tries to identify the port (the first one that yields a positive result will be used):
+Traefik also attempts to determine the right port (which is a [non-trivial matter in Marathon](https://mesosphere.github.io/marathon/docs/ports.html)) from the following sources:
 
-1. A arbitrary port specified through the `traefik.http.services.serviceName.loadbalancer.server.port=8080`
-1. The task port (possibly indexed through the `traefik.http.services.serviceName.loadbalancer.server.port=index:0` label, otherwise the first one).
-1. The port from the application's `portDefinitions` field (possibly indexed through the `traefik.http.services.serviceName.loadbalancer.server.port=index:0` label, otherwise the first one).
-1. The port from the application's `ipAddressPerTask` field (possibly indexed through the `traefik.http.services.serviceName.loadbalancer.server.port=index:0` label, otherwise the first one).
+1. An arbitrary port specified through label `traefik.http.services.serviceName.loadbalancer.server.port=8080`
+1. The task port.
+1. The port from the application's `portDefinitions` field.
+1. The port from the application's `ipAddressPerTask` field.
+
+### Port label syntax
+
+To select a port, you can either
+
+- specify the port directly: `traefik.http.services.serviceName.loadbalancer.server.port=8080`
+- specify a port index: `traefik.http.services.serviceName.loadbalancer.server.port=index:0`
+- specify a port name: `traefik.http.services.serviceName.loadbalancer.server.port=name:http`
+- otherwise the first one is selected.
 
 ## Achieving high availability
 

pkg/provider/marathon/builder_test.go

@@ -53,10 +53,11 @@ func constraint(value string) func(*marathon.Application) {
 	}
 }
 
-func portDefinition(port int) func(*marathon.Application) {
+func portDefinition(port int, name string) func(*marathon.Application) {
 	return func(app *marathon.Application) {
 		app.AddPortDefinition(marathon.PortDefinition{
 			Port: &port,
+			Name: name,
 		})
 	}
 }

pkg/provider/marathon/config.go

@@ -373,7 +373,7 @@ func getPort(task marathon.Task, app marathon.Application, serverPort string) (s
 // one of the available port. The first such found port is returned unless an
 // optional index is provided.
 func processPorts(app marathon.Application, task marathon.Task, serverPort string) (int, error) {
-	if len(serverPort) > 0 && !strings.HasPrefix(serverPort, "index:") {
+	if len(serverPort) > 0 && !(strings.HasPrefix(serverPort, "index:") || strings.HasPrefix(serverPort, "name:")) {
 		port, err := strconv.Atoi(serverPort)
 		if err != nil {
 			return 0, err
@@ -386,6 +386,17 @@ func processPorts(app marathon.Application, task marathon.Task, serverPort strin
 		}
 	}
 
+	if strings.HasPrefix(serverPort, "name:") {
+		name := strings.TrimPrefix(serverPort, "name:")
+		port := retrieveNamedPort(app, name)
+
+		if port == 0 {
+			return 0, fmt.Errorf("no port with name %s", name)
+		}
+
+		return port, nil
+	}
+
 	ports := retrieveAvailablePorts(app, task)
 	if len(ports) == 0 {
 		return 0, errors.New("no port found")
@@ -393,8 +404,8 @@ func processPorts(app marathon.Application, task marathon.Task, serverPort strin
 
 	portIndex := 0
 	if strings.HasPrefix(serverPort, "index:") {
-		split := strings.SplitN(serverPort, ":", 2)
-		index, err := strconv.Atoi(split[1])
+		indexString := strings.TrimPrefix(serverPort, "index:")
+		index, err := strconv.Atoi(indexString)
 		if err != nil {
 			return 0, err
 		}
@@ -402,11 +413,35 @@ func processPorts(app marathon.Application, task marathon.Task, serverPort strin
 		if index < 0 || index > len(ports)-1 {
 			return 0, fmt.Errorf("index %d must be within range (0, %d)", index, len(ports)-1)
 		}
+
 		portIndex = index
 	}
+
 	return ports[portIndex], nil
 }
 
+func retrieveNamedPort(app marathon.Application, name string) int {
+	// Using port definition if available
+	if app.PortDefinitions != nil && len(*app.PortDefinitions) > 0 {
+		for _, def := range *app.PortDefinitions {
+			if def.Port != nil && *def.Port > 0 && def.Name == name {
+				return *def.Port
+			}
+		}
+	}
+
+	// If using IP-per-task using this port definition
+	if app.IPAddressPerTask != nil && app.IPAddressPerTask.Discovery != nil && len(*(app.IPAddressPerTask.Discovery.Ports)) > 0 {
+		for _, def := range *(app.IPAddressPerTask.Discovery.Ports) {
+			if def.Number > 0 && def.Name == name {
+				return def.Number
+			}
+		}
+	}
+
+	return 0
+}
+
 func retrieveAvailablePorts(app marathon.Application, task marathon.Task) []int {
 	// Using default port configuration
 	if len(task.Ports) > 0 {

pkg/provider/marathon/config_test.go

@@ -1941,13 +1941,53 @@ func TestGetServer(t *testing.T) {
 				error: `unable to process ports for /app taskID: strconv.Atoi: parsing "aaa": invalid syntax`,
 			},
 		},
+		{
+			desc:     "with port name",
+			provider: Provider{},
+			app: application(
+				appID("/app"),
+				portDefinition(80, "fist-port"),
+				portDefinition(81, "second-port"),
+				portDefinition(82, "third-port"),
+				withTasks(localhostTask()),
+			),
+			extraConf: configuration{},
+			defaultServer: dynamic.Server{
+				Scheme: "http",
+				Port:   "name:third-port",
+			},
+			expected: expected{
+				server: dynamic.Server{
+					URL: "http://localhost:82",
+				},
+			},
+		},
+		{
+			desc:     "with port name not found",
+			provider: Provider{},
+			app: application(
+				appID("/app"),
+				portDefinition(80, "fist-port"),
+				portDefinition(81, "second-port"),
+				portDefinition(82, "third-port"),
+				withTasks(localhostTask()),
+			),
+			extraConf: configuration{},
+			defaultServer: dynamic.Server{
+				Scheme: "http",
+				Port:   "name:other-name",
+			},
+			expected: expected{
+				error: `unable to process ports for /app taskID: no port with name other-name`,
+			},
+		},
 		{
 			desc:     "with application port and no task port",
 			provider: Provider{},
 			app: application(
 				appID("/app"),
 				appPorts(80),
-				portDefinition(80),
+				portDefinition(80, "http"),
 				withTasks(localhostTask()),
 			),
 			extraConf: configuration{},