Add ability to manage fallback network config on PhotonOS (#941)

Currently cloud-init generates fallback network config on various
scenarios.

For example:
1. When no DS found
2. There is no 'network' info given in DS metadata.
3. If a DS gives a network config once and upon reboot if DS doesn't
   give any network info, previously set network data will be
   overridden.

A newly introduced key in cloud.cfg.tmpl can be used to control this
behavior on PhotonOS.

Also, if OS comes with a set of default network files(configs), like in
PhotonOS, cloud-init should not overwrite them by default.

This change also includes some nitpicking changes of reorganizing few
config variables.

Signed-off-by: Shreenidhi Shedi <sshedi@vmware.com>

5 files changed, 82 insertions, 2 deletions

diff --git a/cloudinit/distros/photon.py b/cloudinit/distros/photon.py
index 3ef5dd40..61e270c0 100644
--- a/cloudinit/distros/photon.py
+++ b/cloudinit/distros/photon.py
@@ -5,6 +5,7 @@
 #
 # This file is part of cloud-init. See LICENSE file for license information.
 
+from cloudinit import net
 from cloudinit import util
 from cloudinit import subp
 from cloudinit import distros
@@ -54,6 +55,20 @@ class Distro(distros.Distro):
             util.logexc(LOG, 'Command %s failed', cmd)
             return False, None, None
 
+    def generate_fallback_config(self):
+        key = 'disable_fallback_netcfg'
+        disable_fallback_netcfg = self._cfg.get(key, True)
+        LOG.debug('%s value is: %s', key, disable_fallback_netcfg)
+
+        if not disable_fallback_netcfg:
+            return net.generate_fallback_config()
+
+        LOG.info(
+            'Skipping generate_fallback_config. Rely on PhotonOS default '
+            'network config'
+        )
+        return None
+
     def apply_locale(self, locale, out_fn=None):
         # This has a dependancy on glibc-i18n, user need to manually install it
         # and enable the option in cloud.cfg
diff --git a/config/cloud.cfg.tmpl b/config/cloud.cfg.tmpl
index f918d919..2314d893 100644
--- a/config/cloud.cfg.tmpl
+++ b/config/cloud.cfg.tmpl
@@ -18,9 +18,10 @@ users:
    - default
 {% endif %}
 
-# VMware guest customization.
 {% if variant in ["photon"] %}
+# VMware guest customization.
 disable_vmware_customization: true
+manage_etc_hosts: false
 {% endif %}
 
 # If this is set, 'root' will not be able to ssh in and they
@@ -306,10 +307,15 @@ system_info:
    paths:
       cloud_dir: /var/lib/cloud/
       templates_dir: /etc/cloud/templates/
+   network:
+      renderers: ['networkd']
 
    ssh_svcname: sshd
 
-#manage_etc_hosts: true
+   # If set to true, cloud-init will not use fallback network config.
+   # In Photon, we have default network settings, hence if network settings are
+   # not explicitly given in metadata, don't use fallback network config.
+   disable_fallback_netcfg: true
 {% endif %}
 {% if variant in ["freebsd", "netbsd", "openbsd"] %}
    network:
diff --git a/doc/rtd/topics/availability.rst b/doc/rtd/topics/availability.rst
index a45a49d6..b84b6076 100644
--- a/doc/rtd/topics/availability.rst
+++ b/doc/rtd/topics/availability.rst
@@ -26,6 +26,7 @@ OpenBSD and DragonFlyBSD:
 - Gentoo Linux
 - NetBSD
 - OpenBSD
+- Photon OS
 - RHEL/CentOS
 - SLES/openSUSE
 - Ubuntu
diff --git a/doc/rtd/topics/network-config.rst b/doc/rtd/topics/network-config.rst
index 5f7a74f8..8eb7a31b 100644
--- a/doc/rtd/topics/network-config.rst
+++ b/doc/rtd/topics/network-config.rst
@@ -104,6 +104,13 @@ interface given the information it has available.
 Finally after selecting the "right" interface, a configuration is
 generated and applied to the system.
 
+.. note::
+
+   PhotonOS disables fallback networking configuration by default leaving
+   network unrendered when no other network config is provided.
+   If fallback config is still desired on PhotonOS, it can be enabled by
+   providing `disable_fallback_netcfg: false` in
+   `/etc/cloud/cloud.cfg:sys_config` settings.
 
 Network Configuration Sources
 =============================
diff --git a/tests/unittests/test_distros/test_photon.py b/tests/unittests/test_distros/test_photon.py
new file mode 100644
index 00000000..775f37ac
--- /dev/null
+++ b/tests/unittests/test_distros/test_photon.py
@@ -0,0 +1,51 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+
+from . import _get_distro
+from cloudinit import util
+from cloudinit.tests.helpers import mock
+from cloudinit.tests.helpers import CiTestCase
+
+SYSTEM_INFO = {
+    'paths': {
+        'cloud_dir': '/var/lib/cloud/',
+        'templates_dir': '/etc/cloud/templates/',
+    },
+    'network': {'renderers': 'networkd'},
+}
+
+
+class TestPhoton(CiTestCase):
+    with_logs = True
+    distro = _get_distro('photon', SYSTEM_INFO)
+    expected_log_line = 'Rely on PhotonOS default network config'
+
+    def test_network_renderer(self):
+        self.assertEqual(self.distro._cfg['network']['renderers'], 'networkd')
+
+    def test_get_distro(self):
+        self.assertEqual(self.distro.osfamily, 'photon')
+
+    def test_write_hostname(self):
+        hostname = 'myhostname'
+        hostfile = self.tmp_path('hostfile')
+        self.distro._write_hostname(hostname, hostfile)
+        self.assertEqual(hostname + '\n', util.load_file(hostfile))
+
+    @mock.patch('cloudinit.net.generate_fallback_config')
+    def test_fallback_netcfg(self, m_fallback_cfg):
+
+        key = 'disable_fallback_netcfg'
+        # Don't use fallback if no setting given
+        self.logs.truncate(0)
+        assert(self.distro.generate_fallback_config() is None)
+        self.assertIn(self.expected_log_line, self.logs.getvalue())
+
+        self.logs.truncate(0)
+        self.distro._cfg[key] = True
+        assert(self.distro.generate_fallback_config() is None)
+        self.assertIn(self.expected_log_line, self.logs.getvalue())
+
+        self.logs.truncate(0)
+        self.distro._cfg[key] = False
+        assert(self.distro.generate_fallback_config() is not None)
+        self.assertNotIn(self.expected_log_line, self.logs.getvalue())