Add support for placement preferences docker-compose v3.3+ (#1425)

pkg/loader/compose/compose_test.go

@@ -595,6 +595,11 @@ func TestCheckPlacementCustomLabels(t *testing.T) {
 			"node.labels.something == anything",
 			"node.labels.monitor != xxx",
 		},
+		Preferences: []types.PlacementPreferences{
+			{Spread: "node.labels.zone"},
+			{Spread: "foo"},
+			{Spread: "node.labels.ssd"},
+		},
 	}
 	output := loadV3Placement(placement)
 
@@ -605,10 +610,22 @@ func TestCheckPlacementCustomLabels(t *testing.T) {
 		NegativeConstraints: map[string]string{
 			"monitor": "xxx",
 		},
+		Preferences: []string{
+			"zone", "ssd",
+		},
 	}
 
 	checkConstraints(t, "positive", output.PositiveConstraints, expected.PositiveConstraints)
 	checkConstraints(t, "negative", output.NegativeConstraints, expected.NegativeConstraints)
+
+	if len(output.Preferences) != len(expected.Preferences) {
+		t.Errorf("preferences len is not equal, expected %d, got %d", len(expected.Preferences), len(output.Preferences))
+	}
+	for i := range output.Preferences {
+		if output.Preferences[i] != expected.Preferences[i] {
+			t.Errorf("preference is not equal, expected %s, got %s", expected.Preferences[i], output.Preferences[i])
+		}
+	}
 }
 
 func checkConstraints(t *testing.T, caseName string, output, expected map[string]string) {

pkg/loader/compose/v3.go

@@ -137,9 +137,11 @@ func loadV3Placement(placement types.Placement) kobject.Placement {
 	komposePlacement := kobject.Placement{
 		PositiveConstraints: make(map[string]string),
 		NegativeConstraints: make(map[string]string),
+		Preferences:         make([]string, 0, len(placement.Preferences)),
 	}
+
+	// Convert constraints
 	equal, notEqual := " == ", " != "
-	errMsg := " constraints in placement is not supported, only 'node.hostname', 'engine.labels.operatingsystem' and 'node.labels.xxx' (ex: node.labels.something == anything) is supported as a constraint "
 	for _, j := range placement.Constraints {
 		operator := equal
 		if strings.Contains(j, notEqual) {
@@ -147,19 +149,13 @@ func loadV3Placement(placement types.Placement) kobject.Placement {
 		}
 		p := strings.Split(j, operator)
 		if len(p) < 2 {
-			log.Warn(p[0], errMsg)
+			log.Warnf("Failed to parse placement constraints %s, the correct format is 'label == xxx'", j)
 			continue
 		}
 
-		var key string
-		if p[0] == "node.hostname" {
-			key = "kubernetes.io/hostname"
-		} else if p[0] == "engine.labels.operatingsystem" {
-			key = "beta.kubernetes.io/os"
-		} else if strings.HasPrefix(p[0], "node.labels.") {
-			key = strings.TrimPrefix(p[0], "node.labels.")
-		} else {
-			log.Warn(p[0], errMsg)
+		key, err := convertDockerLabel(p[0])
+		if err != nil {
+			log.Warn("Ignore placement constraints: ", err.Error())
 			continue
 		}
 
@@ -169,9 +165,36 @@ func loadV3Placement(placement types.Placement) kobject.Placement {
 			komposePlacement.NegativeConstraints[key] = p[1]
 		}
 	}
+
+	// Convert preferences
+	for _, p := range placement.Preferences {
+		// Spread is the only supported strategy currently
+		label, err := convertDockerLabel(p.Spread)
+		if err != nil {
+			log.Warn("Ignore placement preferences: ", err.Error())
+			continue
+		}
+		komposePlacement.Preferences = append(komposePlacement.Preferences, label)
+	}
 	return komposePlacement
 }
 
+// Convert docker label to k8s label
+func convertDockerLabel(dockerLabel string) (string, error) {
+	switch dockerLabel {
+	case "node.hostname":
+		return "kubernetes.io/hostname", nil
+	case "engine.labels.operatingsystem":
+		return "kubernetes.io/os", nil
+	default:
+		if strings.HasPrefix(dockerLabel, "node.labels.") {
+			return strings.TrimPrefix(dockerLabel, "node.labels."), nil
+		}
+	}
+	errMsg := fmt.Sprint(dockerLabel, " is not supported, only 'node.hostname', 'engine.labels.operatingsystem' and 'node.labels.xxx' (ex: node.labels.something == anything) is supported")
+	return "", errors.New(errMsg)
+}
+
 // Convert the Docker Compose v3 volumes to []string (the old way)
 // TODO: Check to see if it's a "bind" or "volume". Ignore for now.
 // TODO: Refactor it similar to loadV3Ports