Warn on empty network key (#1990)

It is possible to create an empty network key that fails
over to fallback network config without warning. Fix it.

2 files changed, 22 insertions, 0 deletions

diff --git a/cloudinit/stages.py b/cloudinit/stages.py
index 58b53d96..9494a0bf 100644
--- a/cloudinit/stages.py
+++ b/cloudinit/stages.py
@@ -853,6 +853,8 @@ class Init:
                 return (None, cfg_source)
             if ncfg:
                 return (ncfg, cfg_source)
+        if not self.cfg.get("network", True):
+            LOG.warning("Empty network config found")
         return (
             self.distro.generate_fallback_config(),
             NetworkConfigSource.FALLBACK,
diff --git a/tests/unittests/test_stages.py b/tests/unittests/test_stages.py
index 7fde2bac..15a7e973 100644
--- a/tests/unittests/test_stages.py
+++ b/tests/unittests/test_stages.py
@@ -356,6 +356,26 @@ class TestInit:
         ) == self.init._find_networking_config()
         assert "network config disabled" not in caplog.text
 
+    @mock.patch(M_PATH + "cmdline.read_initramfs_config", return_value={})
+    @mock.patch(M_PATH + "cmdline.read_kernel_cmdline_config", return_value={})
+    def test_warn_on_empty_network(self, m_cmdline, m_initramfs, caplog):
+        """funky whitespace can lead to a network key that is None, which then
+        causes fallback. Test warning log on empty network key.
+        """
+        m_cmdline.return_value = {}  # Kernel doesn't disable networking
+        m_initramfs.return_value = {}  # no initramfs network config
+        # Neither datasource nor system_info disable or provide network
+        self.init._cfg = {
+            "system_info": {"paths": {"cloud_dir": self.tmpdir}},
+            "network": None,
+        }
+        self.init.datasource = FakeDataSource(network_config={"network": None})
+
+        self.init.distro.generate_fallback_config = lambda: {}
+
+        self.init._find_networking_config()
+        assert "Empty network config found" in caplog.text
+
     def test_apply_network_config_disabled(self, caplog):
         """Log when network is disabled by upgraded-network."""
         disable_file = os.path.join(