diff --git a/internal/metadata/handle.go b/internal/metadata/handle.go
index d34dd20..8f3d1f4 100644
--- a/internal/metadata/handle.go
+++ b/internal/metadata/handle.go
@@ -8,33 +8,37 @@ import (
 )
 
 func StartMetadata(config NoCloudConfig, cfg *configuration.Config, dryrun bool) error {
+	if err := WriteNoCloudFiles(config, cfg.Metadata.RunDir); err != nil {
+		return fmt.Errorf("write nocloud files for %s: %w", config.Name, err)
+	}
+	if dryrun {
+		return nil
+	}
+
 	service, err := systemd.New()
 	if err != nil {
 		return fmt.Errorf("failed to connect to systemd: %w", err)
 	}
 	defer service.Close()
 
-	LoadNcCloudInDB(config, cfg.Metadata.RunDir)
-	if !dryrun {
-		if err := service.Start("metadata@" + config.Name + ".service"); err != nil {
-			return fmt.Errorf("failed to start metadata@%s: %w", config.Name, err)
-		}
+	if err := service.Start("metadata@" + config.Name + ".service"); err != nil {
+		return fmt.Errorf("failed to start metadata@%s: %w", config.Name, err)
 	}
 	return nil
 }
 
 func StopMetadata(vmName string, cfg *configuration.Config, dryrun bool) error {
-	service, err := systemd.New()
-	if err != nil {
-		return fmt.Errorf("failed to connect to systemd: %w", err)
-	}
-	defer service.Close()
-
-	UnLoadNoCloudInDB(vmName, cfg.Metadata.RunDir)
 	if !dryrun {
+		service, err := systemd.New()
+		if err != nil {
+			return fmt.Errorf("failed to connect to systemd: %w", err)
+		}
+		defer service.Close()
+
 		if err := service.Stop("metadata@" + vmName + ".service"); err != nil {
 			return fmt.Errorf("failed to stop metadata@%s: %w", vmName, err)
 		}
 	}
-	return nil
+
+	return RemoveNoCloudFiles(vmName, cfg.Metadata.RunDir)
 }
diff --git a/internal/metadata/metadata_test.go b/internal/metadata/metadata_test.go
index cc54530..4efff81 100644
--- a/internal/metadata/metadata_test.go
+++ b/internal/metadata/metadata_test.go
@@ -25,6 +25,21 @@ func useTestDir(t *testing.T) string {
 	return t.TempDir()
 }
 
+
+func mustWrite(t *testing.T, cfg NoCloudConfig, dir string) {
+	t.Helper()
+	if err := WriteNoCloudFiles(cfg, dir); err != nil {
+		t.Fatalf("WriteNoCloudFiles : %v", err)
+	}
+}
+
+func mustRemove(t *testing.T, vmName, dir string) {
+	t.Helper()
+	if err := RemoveNoCloudFiles(vmName, dir); err != nil {
+		t.Fatalf("RemoveNoCloudFiles : %v", err)
+	}
+}
+
 // --- RenderConfig ---
 
 func TestRenderConfig_MetaData(t *testing.T) {
@@ -74,14 +89,23 @@ func TestRenderConfig_NetworkConfig(t *testing.T) {
 	}
 }
 
-func TestRenderConfig_UserData(t *testing.T) {
-	cfg := newCfg()
-	out, err := RenderConfig("templates/user-data.tmpl", cfg)
+func TestRenderConfig_UserData_DefaultIsEmpty(t *testing.T) {
+	doc, err := renderDocument(DocUserData, newCfg())
 	if err != nil {
-		t.Fatalf("RenderConfig user-data : %v", err)
+		t.Fatalf("renderDocument user-data : %v", err)
 	}
-	if !strings.Contains(out, "passwd -d root") {
-		t.Errorf("user-data inattendu :\n%s", out)
+	if doc != "" {
+		t.Errorf("le user-data par défaut doit être vide, obtenu :\n%q", doc)
+	}
+}
+
+func TestRenderConfig_UserData_NeverTouchesRootPassword(t *testing.T) {
+	doc, err := renderDocument(DocUserData, newCfg())
+	if err != nil {
+		t.Fatalf("renderDocument user-data : %v", err)
+	}
+	if strings.Contains(doc, "passwd -d root") {
+		t.Errorf("l'agent ne doit imposer aucune modification du compte root :\n%s", doc)
 	}
 }
 
@@ -104,21 +128,21 @@ func TestRenderConfig_SpecialCharsInName(t *testing.T) {
 	}
 }
 
-// --- LoadNcCloudInDB / UnLoadNoCloudInDB ---
+// --- WriteNoCloudFiles / RemoveNoCloudFiles ---
 
 func readTestFile(t *testing.T, dir, vmName, name string) string {
 	t.Helper()
 	b, err := os.ReadFile(filepath.Join(dir, vmName, name))
 	if err != nil {
-		t.Errorf("fichier %q absent après LoadNcCloudInDB : %v", name, err)
+		t.Errorf("fichier %q absent après WriteNoCloudFiles : %v", name, err)
 		return ""
 	}
 	return string(b)
 }
 
-func TestLoadNcCloudInDB_StoresAllFiles(t *testing.T) {
+func TestWriteNoCloudFiles_StoresAllFiles(t *testing.T) {
 	dir := useTestDir(t)
-	LoadNcCloudInDB(newCfg(), dir)
+	mustWrite(t, newCfg(), dir)
 
 	files := []string{"meta-data", "user-data", "network-config", "vendor-data", "vpc", "bind_ip", "bind_port"}
 	for _, f := range files {
@@ -129,9 +153,9 @@ func TestLoadNcCloudInDB_StoresAllFiles(t *testing.T) {
 	}
 }
 
-func TestLoadNcCloudInDB_VpcAndBindValues(t *testing.T) {
+func TestWriteNoCloudFiles_VpcAndBindValues(t *testing.T) {
 	dir := useTestDir(t)
-	LoadNcCloudInDB(newCfg(), dir)
+	mustWrite(t, newCfg(), dir)
 
 	if vpc := readTestFile(t, dir, "vm1", "vpc"); vpc != "vpc-test" {
 		t.Errorf("vpc attendu %q, obtenu %q", "vpc-test", vpc)
@@ -144,26 +168,26 @@ func TestLoadNcCloudInDB_VpcAndBindValues(t *testing.T) {
 	}
 }
 
-func TestUnLoadNoCloudInDB_RemovesAllFiles(t *testing.T) {
+func TestRemoveNoCloudFiles_RemovesAllFiles(t *testing.T) {
 	dir := useTestDir(t)
-	LoadNcCloudInDB(newCfg(), dir)
-	UnLoadNoCloudInDB("vm1", dir)
+	mustWrite(t, newCfg(), dir)
+	mustRemove(t, "vm1", dir)
 
 	if _, err := os.Stat(filepath.Join(dir, "vm1")); !os.IsNotExist(err) {
-		t.Error("répertoire vm1 devrait être supprimé après UnLoadNoCloudInDB")
+		t.Error("répertoire vm1 devrait être supprimé après RemoveNoCloudFiles")
 	}
 }
 
-func TestUnLoadNoCloudInDB_DoesNotAffectOtherVMs(t *testing.T) {
+func TestRemoveNoCloudFiles_DoesNotAffectOtherVMs(t *testing.T) {
 	dir := useTestDir(t)
 
 	cfg1 := newCfg()
 	cfg2 := newCfg()
 	cfg2.Name = "vm2"
-	LoadNcCloudInDB(cfg1, dir)
-	LoadNcCloudInDB(cfg2, dir)
+	mustWrite(t, cfg1, dir)
+	mustWrite(t, cfg2, dir)
 
-	UnLoadNoCloudInDB("vm1", dir)
+	mustRemove(t, "vm1", dir)
 
 	if _, err := os.Stat(filepath.Join(dir, "vm2", "vpc")); err != nil {
 		t.Errorf("vm2 ne devrait pas être supprimée : %v", err)
@@ -264,3 +288,138 @@ func TestRootHandler_ContentType(t *testing.T) {
 		t.Errorf("Content-Type attendu text/yaml, obtenu %q", ct)
 	}
 }
+
+// --- vendor-data : blocs conditionnels ---
+
+func vendorData(t *testing.T, password, sshkey string) string {
+	t.Helper()
+	cfg := newCfg()
+	cfg.Password = password
+	cfg.SSHKEY = sshkey
+	out, err := renderDocument(DocVendorData, cfg)
+	if err != nil {
+		t.Fatalf("renderDocument vendor-data : %v", err)
+	}
+	return out
+}
+
+func TestVendorData_NoCredentials_EmitsNothing(t *testing.T) {
+	out := vendorData(t, "", "")
+	if out != "" {
+		t.Errorf("sans mot de passe ni clé, aucun compte ne doit être créé :\n%s", out)
+	}
+}
+
+func TestVendorData_NoCredentials_NeverEmitsEmptyValues(t *testing.T) {
+	out := vendorData(t, "", "")
+	for _, forbidden := range []string{`passwd: ""`, `- ""`, "lock_passwd: false"} {
+		if strings.Contains(out, forbidden) {
+			t.Errorf("valeur vide %q émise :\n%s", forbidden, out)
+		}
+	}
+}
+
+func TestVendorData_PasswordOnly(t *testing.T) {
+	out := vendorData(t, "$6$rounds$hash", "")
+	if !strings.Contains(out, `passwd: "$6$rounds$hash"`) {
+		t.Errorf("hash absent :\n%s", out)
+	}
+	if !strings.Contains(out, "lock_passwd: false") {
+		t.Errorf("un compte avec mot de passe doit être déverrouillé :\n%s", out)
+	}
+	if strings.Contains(out, "ssh_authorized_keys") {
+		t.Errorf("aucune clé fournie, le bloc ne doit pas apparaître :\n%s", out)
+	}
+}
+
+func TestVendorData_SSHKeyOnly_LocksPassword(t *testing.T) {
+	out := vendorData(t, "", "ssh-ed25519 AAAA user@host")
+	if !strings.Contains(out, "ssh-ed25519 AAAA user@host") {
+		t.Errorf("clé absente :\n%s", out)
+	}
+	if strings.Contains(out, "\n    passwd:") {
+		t.Errorf("aucun mot de passe fourni, le champ ne doit pas apparaître :\n%s", out)
+	}
+	if !strings.Contains(out, "lock_passwd: true") {
+		t.Errorf("sans mot de passe le compte doit rester verrouillé, sinon il devient un compte sudo sans mot de passe :\n%s", out)
+	}
+}
+
+func TestVendorData_BothCredentials(t *testing.T) {
+	out := vendorData(t, "$6$hash", "ssh-ed25519 AAAA user@host")
+	for _, expected := range []string{"#cloud-config", "name: syonad", `passwd: "$6$hash"`, "lock_passwd: false", "ssh-ed25519 AAAA user@host"} {
+		if !strings.Contains(out, expected) {
+			t.Errorf("%q absent :\n%s", expected, out)
+		}
+	}
+}
+
+func TestVendorData_CloudConfigHeaderIsFirstLine(t *testing.T) {
+	out := vendorData(t, "$6$hash", "")
+	if !strings.HasPrefix(out, "#cloud-config\n") {
+		t.Errorf("cloud-init exige #cloud-config en première ligne :\n%q", out)
+	}
+}
+
+// --- documents fournis par l'appelant ---
+
+func TestRenderDocument_VerbatimOverridesTemplate(t *testing.T) {
+	cfg := newCfg()
+	supplied := "#cloud-config\npackages:\n  - nginx\n"
+	cfg.Documents = map[string]string{DocUserData: supplied}
+
+	out, err := renderDocument(DocUserData, cfg)
+	if err != nil {
+		t.Fatalf("renderDocument : %v", err)
+	}
+	if out != supplied {
+		t.Errorf("le document fourni doit être écrit verbatim :\nattendu %q\nobtenu  %q", supplied, out)
+	}
+}
+
+func TestRenderDocument_EmptySuppliedDocumentIsHonoured(t *testing.T) {
+	cfg := newCfg()
+	cfg.Documents = map[string]string{DocVendorData: ""}
+
+	out, err := renderDocument(DocVendorData, cfg)
+	if err != nil {
+		t.Fatalf("renderDocument : %v", err)
+	}
+	if out != "" {
+		t.Errorf("un document explicitement vide ne doit pas retomber sur le template :\n%s", out)
+	}
+}
+
+func TestWriteNoCloudFiles_WritesSuppliedDocument(t *testing.T) {
+	dir := useTestDir(t)
+	cfg := newCfg()
+	cfg.Documents = map[string]string{DocUserData: "#cloud-config\nruncmd:\n  - [ls]\n"}
+	mustWrite(t, cfg, dir)
+
+	if got := readTestFile(t, dir, "vm1", "user-data"); got != cfg.Documents[DocUserData] {
+		t.Errorf("user-data servi différent de celui fourni :\n%q", got)
+	}
+}
+
+// --- remontée des erreurs ---
+
+func TestWriteNoCloudFiles_ReturnsErrorOnUnwritableDir(t *testing.T) {
+	if os.Geteuid() == 0 {
+		t.Skip("root ignore les permissions de fichiers")
+	}
+	dir := useTestDir(t)
+	if err := os.Chmod(dir, 0500); err != nil {
+		t.Fatalf("chmod : %v", err)
+	}
+	t.Cleanup(func() { os.Chmod(dir, 0700) })
+
+	if err := WriteNoCloudFiles(newCfg(), dir); err == nil {
+		t.Error("une écriture impossible doit remonter une erreur : une VM ne doit jamais démarrer sans métadonnées en silence")
+	}
+}
+
+func TestRemoveNoCloudFiles_AbsentDirIsNotAnError(t *testing.T) {
+	if err := RemoveNoCloudFiles("jamais-creee", useTestDir(t)); err != nil {
+		t.Errorf("supprimer une VM sans fichiers ne doit pas échouer : %v", err)
+	}
+}
diff --git a/internal/metadata/render.go b/internal/metadata/render.go
index 0d4fd59..a038097 100644
--- a/internal/metadata/render.go
+++ b/internal/metadata/render.go
@@ -3,14 +3,27 @@ package metadata
 import (
 	"bytes"
 	"embed"
+	"fmt"
 	"os"
 	"path/filepath"
+	"strings"
 	"text/template"
 )
 
 //go:embed templates/*.tmpl
 var templateFS embed.FS
 
+const (
+	DocMetaData      = "meta-data"
+	DocUserData      = "user-data"
+	DocNetworkConfig = "network-config"
+	DocVendorData    = "vendor-data"
+)
+
+func Documents() []string {
+	return []string{DocMetaData, DocUserData, DocNetworkConfig, DocVendorData}
+}
+
 func RenderConfig(path string, cfg NoCloudConfig) (string, error) {
 	tpl, err := template.ParseFS(templateFS, path)
 	if err != nil {
@@ -25,25 +38,55 @@ func RenderConfig(path string, cfg NoCloudConfig) (string, error) {
 	return buf.String(), nil
 }
 
-func LoadNcCloudInDB(config NoCloudConfig, runDir string) {
-	meta_data, _ := RenderConfig("templates/meta-data.tmpl", config)
-	user_data, _ := RenderConfig("templates/user-data.tmpl", config)
-	network_config, _ := RenderConfig("templates/network-config.tmpl", config)
-	vendor_data, _ := RenderConfig("templates/vendor-data.tmpl", config)
+func renderDocument(name string, cfg NoCloudConfig) (string, error) {
+	if doc, ok := cfg.Documents[name]; ok {
+		return doc, nil
+	}
 
+	out, err := RenderConfig("templates/"+name+".tmpl", cfg)
+	if err != nil {
+		return "", fmt.Errorf("render %s: %w", name, err)
+	}
+
+	out = strings.TrimSpace(out)
+	if out == "" {
+		return "", nil
+	}
+	return out + "\n", nil
+}
+
+func WriteNoCloudFiles(config NoCloudConfig, runDir string) error {
 	dir := filepath.Join(runDir, config.Name)
 	if err := os.MkdirAll(dir, 0755); err != nil {
-		return
+		return fmt.Errorf("create %s: %w", dir, err)
 	}
-	os.WriteFile(filepath.Join(dir, "meta-data"), []byte(meta_data), 0644)
-	os.WriteFile(filepath.Join(dir, "user-data"), []byte(user_data), 0644)
-	os.WriteFile(filepath.Join(dir, "network-config"), []byte(network_config), 0644)
-	os.WriteFile(filepath.Join(dir, "vendor-data"), []byte(vendor_data), 0644)
-	os.WriteFile(filepath.Join(dir, "vpc"), []byte(config.VpcName), 0644)
-	os.WriteFile(filepath.Join(dir, "bind_ip"), []byte(config.BindIP), 0644)
-	os.WriteFile(filepath.Join(dir, "bind_port"), []byte(config.BindPort), 0644)
+
+	files := map[string]string{
+		"vpc":       config.VpcName,
+		"bind_ip":   config.BindIP,
+		"bind_port": config.BindPort,
+	}
+	for _, name := range Documents() {
+		doc, err := renderDocument(name, config)
+		if err != nil {
+			return err
+		}
+		files[name] = doc
+	}
+
+	for name, content := range files {
+		path := filepath.Join(dir, name)
+		if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+			return fmt.Errorf("write %s: %w", path, err)
+		}
+	}
+	return nil
 }
 
-func UnLoadNoCloudInDB(vmName string, runDir string) {
-	os.RemoveAll(filepath.Join(runDir, vmName))
+func RemoveNoCloudFiles(vmName string, runDir string) error {
+	dir := filepath.Join(runDir, vmName)
+	if err := os.RemoveAll(dir); err != nil {
+		return fmt.Errorf("remove %s: %w", dir, err)
+	}
+	return nil
 }
diff --git a/internal/metadata/struct.go b/internal/metadata/struct.go
index e706087..2e94cfc 100644
--- a/internal/metadata/struct.go
+++ b/internal/metadata/struct.go
@@ -16,10 +16,11 @@ type ServerConfig struct {
 }
 
 type NoCloudConfig struct {
-	VpcName  string
-	BindIP   string
-	BindPort string
-	Name     string
-	Password string
-	SSHKEY   string
+	VpcName   string
+	BindIP    string
+	BindPort  string
+	Name      string
+	Password  string
+	SSHKEY    string
+	Documents map[string]string
 }
diff --git a/internal/metadata/templates/user-data.tmpl b/internal/metadata/templates/user-data.tmpl
index 84195ab..e69de29 100644
--- a/internal/metadata/templates/user-data.tmpl
+++ b/internal/metadata/templates/user-data.tmpl
@@ -1,3 +0,0 @@
-#!/bin/sh
-
-passwd -d root
diff --git a/internal/metadata/templates/vendor-data.tmpl b/internal/metadata/templates/vendor-data.tmpl
index fe0dcd8..c358f69 100644
--- a/internal/metadata/templates/vendor-data.tmpl
+++ b/internal/metadata/templates/vendor-data.tmpl
@@ -1,9 +1,17 @@
+{{- if or .Password .SSHKEY -}}
 #cloud-config
 users:
   - name: syonad
-    lock_passwd: false
     sudo: ["ALL=(ALL) NOPASSWD:ALL"]
     shell: /bin/bash
+{{- if .Password }}
+    lock_passwd: false
     passwd: "{{ .Password }}"
+{{- else }}
+    lock_passwd: true
+{{- end }}
+{{- if .SSHKEY }}
     ssh_authorized_keys:
       - "{{ .SSHKEY }}"
+{{- end }}
+{{- end }}