fix: omit empty generated hotfix payloads

aks-node-controller/README.md

@@ -256,7 +256,10 @@ application, including variants that share the `azurelinux` OS ID. Their
 distro-specific source changes do not trigger payload generation.
 
 The repository keeps a README placeholder so `go:embed` builds without any
-script hotfix payloads. Generation replaces it with Ubuntu and Azure Linux YAMLs.
+script hotfix payloads. Generation omits any rendered YAML with no `write_files`
+entries (including missing, null, or empty lists) and logs the skipped platform.
+If all platforms are empty, it writes a README placeholder to keep `go:embed` valid.
+This does not add support for non-distro template conditions.
 ANC skips application when the local platform's YAML is absent; no separate
 activation flag is needed. Other payload read errors are logged.
 

hotfix/hotfix_generate_test.py

@@ -56,6 +56,53 @@
 
 
 class HotfixGenerateTests(unittest.TestCase):
+    def test_production_renderer_omits_empty_platform_payloads(self):
+        repository = Path(__file__).resolve().parents[1]
+        lines = (repository / hotfix_generate.TEMPLATE).read_text().splitlines(
+            keepends=True
+        )
+        _, outer_else, end = hotfix_generate.find_block_boundaries(lines)
+        cases = [
+            ("custom cloud only", hotfix_generate.build_hotfix_template(
+                {"initAKSCloud"}, lines[outer_else + 1:end]
+            ), set()),
+            ("missing", "#cloud-config\n", set()),
+            ("null", "write_files:\n", set()),
+            ("empty list", "write_files: []\n", set()),
+            ("ubuntu only", 'write_files:\n{{if not IsMariner}}\n'
+             '- path: /test\n  content: hotfix\n{{end}}\n', {"ubuntu"}),
+            ("both", "write_files:\n- path: /test\n  content: hotfix\n",
+             {"ubuntu", "mariner"}),
+        ]
+        for name, template, platforms in cases:
+            with self.subTest(name=name), tempfile.TemporaryDirectory() as directory:
+                template_path = Path(directory) / "template.yml"
+                template_path.write_text(template)
+                output = Path(directory) / "generated"
+                output.mkdir()
+                for platform in ("ubuntu", "mariner"):
+                    (output / f"rendered_nodecustomdata_{platform}.yml").write_text(
+                        "write_files:\n"  # Stale empty files must also be removed.
+                    )
+                subprocess.run(
+                    ["go", "run", "./hotfix/render-nodecustomdata", "--template",
+                     str(template_path), "--output-dir", str(output)],
+                    cwd=repository, check=True, capture_output=True,
+                )
+                expected = {
+                    f"rendered_nodecustomdata_{platform}.yml" for platform in platforms
+                } or {"README"}
+                self.assertEqual(expected, {path.name for path in output.iterdir()})
+                if name == "custom cloud only":
+                    probe = Path(directory) / "main.go"
+                    probe.write_text('package main\nimport "embed"\n'
+                                     '//go:embed generated\nvar files embed.FS\n'
+                                     'func main() {}\n')
+                    subprocess.run(
+                        ["go", "build", "-o", str(Path(directory) / "probe"), str(probe)],
+                        cwd=repository, check=True, capture_output=True,
+                    )
+
     def test_config_modules_are_independently_hotfixable(self):
         repository = Path(__file__).resolve().parents[1]
         lines = (repository / hotfix_generate.TEMPLATE).read_text().splitlines(

hotfix/render-nodecustomdata/main.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/Azure/agentbaker/pkg/agent"
 	"github.com/Azure/agentbaker/pkg/agent/datamodel"
+	"gopkg.in/yaml.v3"
 )
 
 type platform struct {
@@ -41,6 +42,7 @@ func main() {
 		fatalf("create output directory: %v", err)
 	}
 
+	written := 0
 	for _, target := range platforms {
 		rendered, err := agent.RenderLinuxNodeCustomDataTemplate(
 			templateContent,
@@ -53,10 +55,30 @@ func main() {
 			*outputDir,
 			"rendered_nodecustomdata_"+target.name+".yml",
 		)
+		var payload struct {
+			WriteFiles []yaml.Node `yaml:"write_files"`
+		}
+		if err := yaml.Unmarshal([]byte(rendered), &payload); err != nil {
+			fatalf("parse %s nodecustomdata: %v", target.name, err)
+		}
+		if len(payload.WriteFiles) == 0 {
+			fmt.Fprintf(os.Stderr, "Skipping %s nodecustomdata: no write_files entries\n", target.name)
+			if err := os.Remove(outputPath); err != nil && !os.IsNotExist(err) {
+				fatalf("remove empty %s nodecustomdata: %v", target.name, err)
+			}
+			continue
+		}
 		//nolint:gosec // The caller intentionally selects the output directory; filenames are fixed by this tool.
 		if err := os.WriteFile(outputPath, []byte(rendered), 0o600); err != nil {
 			fatalf("write %s nodecustomdata: %v", target.name, err)
 		}
+		written++
+	}
+	if written == 0 {
+		// Keep at least one file for embedding when every platform is empty.
+		if err := os.WriteFile(filepath.Join(*outputDir, "README"), []byte("No applicable script hotfix payloads.\n"), 0o600); err != nil {
+			fatalf("write empty payload placeholder: %v", err)
+		}
 	}
 }