Make port deterministic

provider/docker/docker.go

@@ -594,9 +594,23 @@ func (p *Provider) getPort(container dockerData) string {
 	if label, err := getLabel(container, "traefik.port"); err == nil {
 		return label
 	}
-	for key := range container.NetworkSettings.Ports {
-		return key.Port()
+
+	// See iteration order in https://blog.golang.org/go-maps-in-action
+	var ports []nat.Port
+	for p := range container.NetworkSettings.Ports {
+		ports = append(ports, p)
 	}
+
+	less := func(i, j nat.Port) bool {
+		return i.Int() < j.Int()
+	}
+	nat.Sort(ports, less)
+
+	if len(ports) > 0 {
+		min := ports[0]
+		return min.Port()
+	}
+
 	return ""
 }
 

provider/docker/docker_test.go

@@ -227,14 +227,13 @@ func TestDockerGetPort(t *testing.T) {
 			})),
 			expected: "80",
 		},
-		// FIXME handle this better..
-		//{
-		//	container: containerJSON(ports(nat.PortMap{
-		//		"80/tcp": {},
-		//		"443/tcp": {},
-		//	})),
-		//	expected: "80",
-		//},
+		{
+			container: containerJSON(ports(nat.PortMap{
+				"80/tcp":  {},
+				"443/tcp": {},
+			})),
+			expected: "80",
+		},
 		{
 			container: containerJSON(labels(map[string]string{
 				"traefik.port": "8080",