Allow disabling of network activation (SC-307) (#1048)

In #919 (81299de), we refactored some of the code used to bring up
networks across distros. Previously, the call to bring up network
interfaces during 'init' stage unintentionally resulted in a no-op
such that network interfaces were NEVER brought up by cloud-init, even
if new network interfaces were found after crawling the metadata.

The code was altered to bring up these discovered network interfaces.
On ubuntu, this results in a 'netplan apply' call during 'init' stage
for any ubuntu-based distro on a datasource that has a NETWORK
dependency. On GCE, this additional 'netplan apply' conflicts with the
google-guest-agent service, resulting in an instance that can no
be connected to.

This commit adds a 'disable_network_activation' option that can be
enabled in /etc/cloud.cfg to disable the activation of network
interfaces in 'init' stage.

LP: #1938299

1 files changed, 43 insertions, 0 deletions

diff --git a/tests/integration_tests/datasources/test_network_dependency.py b/tests/integration_tests/datasources/test_network_dependency.py
new file mode 100644
index 00000000..2e5e3121
--- /dev/null
+++ b/tests/integration_tests/datasources/test_network_dependency.py
@@ -0,0 +1,43 @@
+import pytest
+
+from tests.integration_tests.clouds import IntegrationCloud
+from tests.integration_tests.conftest import get_validated_source
+
+
+def _setup_custom_image(session_cloud: IntegrationCloud):
+    """Like `setup_image` in conftest.py, but with customized content."""
+    source = get_validated_source(session_cloud)
+    if not source.installs_new_version():
+        return
+    client = session_cloud.launch()
+
+    # Insert our "disable_network_activation" file here
+    client.write_to_file(
+        '/etc/cloud/cloud.cfg.d/99-disable-network-activation.cfg',
+        'disable_network_activation: true\n',
+    )
+
+    client.install_new_cloud_init(source)
+    # Even if we're keeping instances, we don't want to keep this
+    # one around as it was just for image creation
+    client.destroy()
+
+
+# This test should be able to work on any cloud whose datasource specifies
+# a NETWORK dependency
+@pytest.mark.gce
+@pytest.mark.ubuntu  # Because netplan
+def test_network_activation_disabled(session_cloud: IntegrationCloud):
+    """Test that the network is not activated during init mode."""
+    _setup_custom_image(session_cloud)
+    with session_cloud.launch() as client:
+        result = client.execute('systemctl status google-guest-agent.service')
+        if not result.ok:
+            raise AssertionError('google-guest-agent is not active:\n%s',
+                                 result.stdout)
+        log = client.read_from_file('/var/log/cloud-init.log')
+
+    assert "Running command ['netplan', 'apply']" not in log
+
+    assert 'Not bringing up newly configured network interfaces' in log
+    assert 'Bringing up newly configured network interfaces' not in log