File cloud-init-noresolv-merge-no-dns-data.diff of Package cloud-init.13036

diff --git a/cloudinit/net/sysconfig.py b/cloudinit/net/sysconfig.py
index be5dede..1708990 100644
--- a/cloudinit/net/sysconfig.py
+++ b/cloudinit/net/sysconfig.py
@@ -578,6 +578,10 @@ class Renderer(renderer.Renderer):
 
     @staticmethod
     def _render_dns(network_state, existing_dns_path=None):
+        # skip writing resolv.conf if network_state doesn't include any input.
+        if not any([len(network_state.dns_nameservers),
+                    len(network_state.dns_searchdomains)]):
+            return None
         content = resolv_conf.ResolvConf("")
         if existing_dns_path and os.path.isfile(existing_dns_path):
             content = resolv_conf.ResolvConf(util.load_file(existing_dns_path))
@@ -585,8 +589,6 @@ class Renderer(renderer.Renderer):
             content.add_nameserver(nameserver)
         for searchdomain in network_state.dns_searchdomains:
             content.add_search_domain(searchdomain)
-        if not str(content):
-            return None
         header = _make_header(';')
         content_str = str(content)
         if not content_str.startswith(header):
diff --git a/tests/unittests/test_net.py b/tests/unittests/test_net.py
index e578992..82eb18f 100644
--- a/tests/unittests/test_net.py
+++ b/tests/unittests/test_net.py
@@ -2701,6 +2701,10 @@ USERCTL=no
         ns = network_state.parse_net_config_data(CONFIG_V1_EXPLICIT_LOOPBACK)
         render_dir = self.tmp_path("render")
         os.makedirs(render_dir)
+        # write an etc/resolv.conf and expect it to not be modified
+        resolvconf = os.path.join(render_dir, 'etc/resolv.conf')
+        content = "# Original Content"
+        util.write_file(resolvconf, content)
         renderer = self._get_renderer()
         renderer.render_network_state(ns, target=render_dir)
         found = dir2dict(render_dir)
@@ -2718,6 +2722,8 @@ TYPE=Ethernet
 USERCTL=no
 """
         self.assertEqual(expected, found[nspath + 'ifcfg-eth0'])
+        # a dhcp only config should not modify resolv.conf
+        self.assertEqual(content, found['/etc/resolv.conf'])
 
     def test_bond_config(self):
         expected_name = 'expected_sysconfig_rhel'
@@ -3202,6 +3208,10 @@ USERCTL=no
         ns = network_state.parse_net_config_data(CONFIG_V1_EXPLICIT_LOOPBACK)
         render_dir = self.tmp_path("render")
         os.makedirs(render_dir)
+        # write an etc/resolv.conf and expect it to not be modified
+        resolvconf = os.path.join(render_dir, 'etc/resolv.conf')
+        content = "# Original Content"
+        util.write_file(resolvconf, content)
         renderer = self._get_renderer()
         renderer.render_network_state(ns, target=render_dir)
         found = dir2dict(render_dir)
@@ -3219,6 +3229,8 @@ TYPE=Ethernet
 USERCTL=no
 """
         self.assertEqual(expected, found[nspath + 'ifcfg-eth0'])
+        # a dhcp only config should not modify resolv.conf
+        self.assertEqual(content, found['/etc/resolv.conf'])
 
     def test_bond_config(self):
         expected_name = 'expected_sysconfig_opensuse'