diff --git a/transform/canonical.go b/transform/canonical.go
index 44484954..d0525f02 100644
--- a/transform/canonical.go
+++ b/transform/canonical.go
@@ -22,9 +22,10 @@ import (
 	"github.com/compose-spec/compose-go/v2/tree"
 )
 
-type transformFunc func(data any, p tree.Path, ignoreParseError bool) (any, error)
+// Func is a function that can transform data at a specific path
+type Func func(data any, p tree.Path, ignoreParseError bool) (any, error)
 
-var transformers = map[tree.Path]transformFunc{}
+var transformers = map[tree.Path]Func{}
 
 func init() {
 	transformers["services.*"] = transformService
diff --git a/transform/defaults.go b/transform/defaults.go
index 041a6897..5d305a1d 100644
--- a/transform/defaults.go
+++ b/transform/defaults.go
@@ -20,14 +20,20 @@ import (
 	"github.com/compose-spec/compose-go/v2/tree"
 )
 
-var defaultValues = map[tree.Path]transformFunc{}
+// DefaultValues contains the default value transformers for compose fields
+var DefaultValues = map[tree.Path]Func{}
 
 func init() {
-	defaultValues["services.*.build"] = defaultBuildContext
-	defaultValues["services.*.secrets.*"] = defaultSecretMount
-	defaultValues["services.*.ports.*"] = portDefaults
-	defaultValues["services.*.deploy.resources.reservations.devices.*"] = deviceRequestDefaults
-	defaultValues["services.*.gpus.*"] = deviceRequestDefaults
+	DefaultValues["services.*.build"] = defaultBuildContext
+	DefaultValues["services.*.secrets.*"] = defaultSecretMount
+	DefaultValues["services.*.ports.*"] = portDefaults
+	DefaultValues["services.*.deploy.resources.reservations.devices.*"] = deviceRequestDefaults
+	DefaultValues["services.*.gpus.*"] = deviceRequestDefaults
+}
+
+// RegisterDefaultValue registers a custom transformer for the given path pattern
+func RegisterDefaultValue(path string, transformer Func) {
+	DefaultValues[tree.Path(path)] = transformer
 }
 
 // SetDefaultValues transforms a compose model to set default values to missing attributes
@@ -40,7 +46,7 @@ func SetDefaultValues(yaml map[string]any) (map[string]any, error) {
 }
 
 func setDefaults(data any, p tree.Path) (any, error) {
-	for pattern, transformer := range defaultValues {
+	for pattern, transformer := range DefaultValues {
 		if p.Matches(pattern) {
 			t, err := transformer(data, p, false)
 			if err != nil {
diff --git a/transform/defaults_test.go b/transform/defaults_test.go
new file mode 100644
index 00000000..89beeb67
--- /dev/null
+++ b/transform/defaults_test.go
@@ -0,0 +1,318 @@
+/*
+   Copyright 2020 The Compose Specification Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package transform
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+
+	"github.com/compose-spec/compose-go/v2/tree"
+	"go.yaml.in/yaml/v3"
+	"gotest.tools/v3/assert"
+)
+
+// exampleEnhancedPortDefaults is an example of an enhanced port defaults function
+// that supports additional protocols and domain names in the published field.
+// This function can be used as a replacement for the default portDefaults
+// by registering it with RegisterDefaultValue.
+//
+// Example usage:
+//
+//	RegisterDefaultValue("services.*.ports.*", exampleEnhancedPortDefaults)
+//
+// This function supports:
+// - Additional protocols: "http", "https", "tcp", "udp"
+// - Domain names in the published field (e.g., "example.com:80")
+// - All existing functionality of the original portDefaults
+func exampleEnhancedPortDefaults(data any, _ tree.Path, _ bool) (any, error) {
+	switch v := data.(type) {
+	case map[string]any:
+		// Set default protocol if not specified
+		if _, ok := v["protocol"]; !ok {
+			v["protocol"] = "tcp"
+		}
+
+		// Set default mode if not specified
+		if _, ok := v["mode"]; !ok {
+			v["mode"] = "ingress"
+		}
+
+		// Enhanced protocol handling with app_protocol
+		protocol, _ := v["protocol"].(string)
+		switch protocol {
+		case "http":
+			if _, ok := v["app_protocol"]; !ok {
+				v["app_protocol"] = "http1.1"
+			}
+		case "https":
+			if _, ok := v["app_protocol"]; !ok {
+				v["app_protocol"] = "http2"
+			}
+		}
+
+		// Auto-generate port name based on target port
+		if _, ok := v["name"]; !ok {
+			if target, ok := v["target"].(int); ok {
+				switch target {
+				case 80:
+					v["name"] = "http"
+				case 443:
+					v["name"] = "https"
+				case 3306:
+					v["name"] = "mysql"
+				case 5432:
+					v["name"] = "postgres"
+				case 6379:
+					v["name"] = "redis"
+				case 27017:
+					v["name"] = "mongodb"
+				default:
+					v["name"] = fmt.Sprintf("port-%d", target)
+				}
+			}
+		}
+
+		// Handle domain names in published field
+		if published, ok := v["published"].(string); ok {
+			// Check if published contains a domain name, very KISS check for this example
+			if strings.Contains(published, ".") && strings.Contains(published, ":") {
+				parts := strings.SplitN(published, ":", 2)
+				if len(parts) == 2 {
+					v["x-published-domain"] = parts[0]
+					v["x-published-port"] = parts[1]
+				}
+			}
+		}
+
+		// Normalize host_ip shortcuts
+		if hostIP, ok := v["host_ip"].(string); ok {
+			switch hostIP {
+			case "localhost":
+				v["host_ip"] = "127.0.0.1"
+			case "*":
+				v["host_ip"] = "0.0.0.0"
+			}
+		}
+
+		// Add monitoring metadata for common ports
+		if target, ok := v["target"].(int); ok {
+			switch target {
+			case 80, 443, 8080, 8443:
+				v["x-metrics-enabled"] = true
+				v["x-metrics-path"] = "/metrics"
+			case 9090: // Prometheus
+				v["x-metrics-enabled"] = true
+				v["x-metrics-type"] = "prometheus"
+			}
+		}
+
+		return v, nil
+	default:
+		return data, nil
+	}
+}
+
+func TestRegisterDefaultValue(t *testing.T) {
+	// Save original transformers, so as not to break possible other tests
+	originalTransformers := make(map[tree.Path]Func)
+	for k, v := range DefaultValues {
+		originalTransformers[k] = v
+	}
+	t.Cleanup(func() {
+		DefaultValues = originalTransformers
+	})
+
+	// Register the function
+	RegisterDefaultValue("services.*.ports.*", exampleEnhancedPortDefaults)
+
+	testCases := []struct {
+		name         string
+		inputYAML    string
+		expectedYAML string
+	}{
+		{
+			name: "basic port with defaults and auto-generated name",
+			inputYAML: `
+services:
+  web:
+    ports:
+      - target: 80
+`,
+			expectedYAML: `
+services:
+  web:
+    ports:
+      - target: 80
+        protocol: tcp
+        mode: ingress
+        name: http
+        x-metrics-enabled: true
+        x-metrics-path: /metrics
+`,
+		},
+		{
+			name: "port with https protocol and app_protocol",
+			inputYAML: `
+services:
+  web:
+    ports:
+      - target: 443
+        protocol: https
+`,
+			expectedYAML: `
+services:
+  web:
+    ports:
+      - target: 443
+        protocol: https
+        app_protocol: http2
+        mode: ingress
+        name: https
+        x-metrics-enabled: true
+        x-metrics-path: /metrics
+`,
+		},
+		{
+			name: "port with domain name in published field",
+			inputYAML: `
+services:
+  web:
+    ports:
+      - target: 80
+        published: "example.com:8080"
+`,
+			expectedYAML: `
+services:
+  web:
+    ports:
+      - target: 80
+        published: "example.com:8080"
+        protocol: tcp
+        mode: ingress
+        name: http
+        x-published-domain: example.com
+        x-published-port: "8080"
+        x-metrics-enabled: true
+        x-metrics-path: /metrics
+`,
+		},
+		{
+			name: "database port with auto-generated name",
+			inputYAML: `
+services:
+  db:
+    ports:
+      - target: 3306
+`,
+			expectedYAML: `
+services:
+  db:
+    ports:
+      - target: 3306
+        protocol: tcp
+        mode: ingress
+        name: mysql
+`,
+		},
+		{
+			name: "host_ip normalization",
+			inputYAML: `
+services:
+  web:
+    ports:
+      - target: 8080
+        host_ip: localhost
+      - target: 8081
+        host_ip: "*"
+`,
+			expectedYAML: `
+services:
+  web:
+    ports:
+      - target: 8080
+        host_ip: "127.0.0.1"
+        protocol: tcp
+        mode: ingress
+        name: port-8080
+        x-metrics-enabled: true
+        x-metrics-path: /metrics
+      - target: 8081
+        host_ip: "0.0.0.0"
+        protocol: tcp
+        mode: ingress
+        name: port-8081
+`,
+		},
+		{
+			name: "prometheus port with monitoring metadata",
+			inputYAML: `
+services:
+  prometheus:
+    ports:
+      - target: 9090
+`,
+			expectedYAML: `
+services:
+  prometheus:
+    ports:
+      - target: 9090
+        protocol: tcp
+        mode: ingress
+        name: port-9090
+        x-metrics-enabled: true
+        x-metrics-type: prometheus
+`,
+		},
+		{
+			name: "http protocol with app_protocol",
+			inputYAML: `
+services:
+  web:
+    ports:
+      - target: 3000
+        protocol: http
+`,
+			expectedYAML: `
+services:
+  web:
+    ports:
+      - target: 3000
+        protocol: http
+        app_protocol: http1.1
+        mode: ingress
+        name: port-3000
+`,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			var input map[string]any
+			err := yaml.Unmarshal([]byte(tc.inputYAML), &input)
+			assert.NilError(t, err)
+
+			var expected map[string]any
+			err = yaml.Unmarshal([]byte(tc.expectedYAML), &expected)
+			assert.NilError(t, err)
+
+			result, err := SetDefaultValues(input)
+			assert.NilError(t, err)
+			assert.DeepEqual(t, result, expected)
+		})
+	}
+}