azure: Add apply_network_config option to disable network from IMDS

Azure generates network configuration from the IMDS service and removes
any preexisting hotplug network scripts which exist in Azure cloud images.
Add a datasource configuration option which allows for writing a default
network configuration which sets up dhcp on eth0 and leave the hotplug
handling to the cloud-image scripts.

To disable network-config from Azure IMDS, add the following to
/etc/cloud/cloud.cfg.d/99-azure-no-imds-network.cfg:
datasource:
  Azure:
    apply_network_config: False

LP: #1798424

3 files changed, 107 insertions, 6 deletions

diff --git a/cloudinit/sources/DataSourceAzure.py b/cloudinit/sources/DataSourceAzure.py
index 39391d01..d0358e96 100644
--- a/cloudinit/sources/DataSourceAzure.py
+++ b/cloudinit/sources/DataSourceAzure.py
@@ -207,7 +207,9 @@ BUILTIN_DS_CONFIG = {
     },
     'disk_aliases': {'ephemeral0': RESOURCE_DISK_PATH},
     'dhclient_lease_file': LEASE_FILE,
+    'apply_network_config': True,  # Use IMDS published network configuration
 }
+# RELEASE_BLOCKER: Xenial and earlier apply_network_config default is False
 
 BUILTIN_CLOUD_CONFIG = {
     'disk_setup': {
@@ -458,7 +460,8 @@ class DataSourceAzure(sources.DataSource):
         except sources.InvalidMetaDataException as e:
             LOG.warning('Could not crawl Azure metadata: %s', e)
             return False
-        if self.distro and self.distro.name == 'ubuntu':
+        if (self.distro and self.distro.name == 'ubuntu' and
+                self.ds_cfg.get('apply_network_config')):
             maybe_remove_ubuntu_network_config_scripts()
 
         # Process crawled data and augment with various config defaults
@@ -619,7 +622,11 @@ class DataSourceAzure(sources.DataSource):
               the blacklisted devices.
         """
         if not self._network_config:
-            self._network_config = parse_network_config(self._metadata_imds)
+            if self.ds_cfg.get('apply_network_config'):
+                nc_src = self._metadata_imds
+            else:
+                nc_src = None
+            self._network_config = parse_network_config(nc_src)
         return self._network_config
 
 
diff --git a/doc/rtd/topics/datasources/azure.rst b/doc/rtd/topics/datasources/azure.rst
index 559011ef..f73c3694 100644
--- a/doc/rtd/topics/datasources/azure.rst
+++ b/doc/rtd/topics/datasources/azure.rst
@@ -57,6 +57,52 @@ in order to use waagent.conf with cloud-init, the following settings are recomme
    ResourceDisk.MountPoint=/mnt
 
 
+Configuration
+-------------
+The following configuration can be set for the datasource in system
+configuration (in `/etc/cloud/cloud.cfg` or `/etc/cloud/cloud.cfg.d/`).
+
+The settings that may be configured are:
+
+ * **agent_command**: Either __builtin__ (default) or a command to run to getcw
+   metadata. If __builtin__, get metadata from walinuxagent. Otherwise run the
+   provided command to obtain metadata.
+ * **apply_network_config**: Boolean set to True to use network configuration
+   described by Azure's IMDS endpoint instead of fallback network config of
+   dhcp on eth0. Default is True. For Ubuntu 16.04 or earlier, default is False.
+ * **data_dir**: Path used to read metadata files and write crawled data.
+ * **dhclient_lease_file**: The fallback lease file to source when looking for
+   custom DHCP option 245 from Azure fabric.
+ * **disk_aliases**: A dictionary defining which device paths should be
+   interpreted as ephemeral images. See cc_disk_setup module for more info.
+ * **hostname_bounce**: A dictionary Azure hostname bounce behavior to react to
+   metadata changes.
+ * **hostname_bounce**: A dictionary Azure hostname bounce behavior to react to
+   metadata changes. Azure will throttle ifup/down in some cases after metadata
+   has been updated to inform dhcp server about updated hostnames.
+ * **set_hostname**: Boolean set to True when we want Azure to set the hostname
+   based on metadata.
+
+An example configuration with the default values is provided below:
+
+.. sourcecode:: yaml
+
+  datasource:
+   Azure:
+    agent_command: __builtin__
+    apply_network_config: true
+    data_dir: /var/lib/waagent
+    dhclient_lease_file: /var/lib/dhcp/dhclient.eth0.leases
+    disk_aliases:
+        ephemeral0: /dev/disk/cloud/azure_resource
+    hostname_bounce:
+        interface: eth0
+        command: builtin
+        policy: true
+        hostname_command: hostname
+    set_hostname: true
+
+
 Userdata
 --------
 Userdata is provided to cloud-init inside the ovf-env.xml file. Cloud-init
diff --git a/tests/unittests/test_datasource/test_azure.py b/tests/unittests/test_datasource/test_azure.py
index 0f4b7bf7..cd6e7e74 100644
--- a/tests/unittests/test_datasource/test_azure.py
+++ b/tests/unittests/test_datasource/test_azure.py
@@ -256,7 +256,8 @@ scbus-1 on xpt0 bus 0
         ])
         return dsaz
 
-    def _get_ds(self, data, agent_command=None, distro=None):
+    def _get_ds(self, data, agent_command=None, distro=None,
+                apply_network=None):
 
         def dsdevs():
             return data.get('dsdevs', [])
@@ -312,6 +313,8 @@ scbus-1 on xpt0 bus 0
             data.get('sys_cfg', {}), distro=distro, paths=self.paths)
         if agent_command is not None:
             dsrc.ds_cfg['agent_command'] = agent_command
+        if apply_network is not None:
+            dsrc.ds_cfg['apply_network_config'] = apply_network
 
         return dsrc
 
@@ -434,14 +437,26 @@ fdescfs            /dev/fd          fdescfs rw              0 0
 
     def test_get_data_on_ubuntu_will_remove_network_scripts(self):
         """get_data will remove ubuntu net scripts on Ubuntu distro."""
+        sys_cfg = {'datasource': {'Azure': {'apply_network_config': True}}}
         odata = {'HostName': "myhost", 'UserName': "myuser"}
         data = {'ovfcontent': construct_valid_ovf_env(data=odata),
-                'sys_cfg': {}}
+                'sys_cfg': sys_cfg}
 
         dsrc = self._get_ds(data, distro='ubuntu')
         dsrc.get_data()
         self.m_remove_ubuntu_network_scripts.assert_called_once_with()
 
+    def test_get_data_on_ubuntu_will_not_remove_network_scripts_disabled(self):
+        """When apply_network_config false, do not remove scripts on Ubuntu."""
+        sys_cfg = {'datasource': {'Azure': {'apply_network_config': False}}}
+        odata = {'HostName': "myhost", 'UserName': "myuser"}
+        data = {'ovfcontent': construct_valid_ovf_env(data=odata),
+                'sys_cfg': sys_cfg}
+
+        dsrc = self._get_ds(data, distro='ubuntu')
+        dsrc.get_data()
+        self.m_remove_ubuntu_network_scripts.assert_not_called()
+
     def test_crawl_metadata_returns_structured_data_and_caches_nothing(self):
         """Return all structured metadata and cache no class attributes."""
         yaml_cfg = "{agent_command: my_command}\n"
@@ -523,8 +538,10 @@ fdescfs            /dev/fd          fdescfs rw              0 0
 
     def test_network_config_set_from_imds(self):
         """Datasource.network_config returns IMDS network data."""
+        sys_cfg = {'datasource': {'Azure': {'apply_network_config': True}}}
         odata = {}
-        data = {'ovfcontent': construct_valid_ovf_env(data=odata)}
+        data = {'ovfcontent': construct_valid_ovf_env(data=odata),
+                'sys_cfg': sys_cfg}
         expected_network_config = {
             'ethernets': {
                 'eth0': {'set-name': 'eth0',
@@ -803,9 +820,10 @@ fdescfs            /dev/fd          fdescfs rw              0 0
     @mock.patch('cloudinit.net.generate_fallback_config')
     def test_imds_network_config(self, mock_fallback):
         """Network config is generated from IMDS network data when present."""
+        sys_cfg = {'datasource': {'Azure': {'apply_network_config': True}}}
         odata = {'HostName': "myhost", 'UserName': "myuser"}
         data = {'ovfcontent': construct_valid_ovf_env(data=odata),
-                'sys_cfg': {}}
+                'sys_cfg': sys_cfg}
 
         dsrc = self._get_ds(data)
         ret = dsrc.get_data()
@@ -825,6 +843,36 @@ fdescfs            /dev/fd          fdescfs rw              0 0
     @mock.patch('cloudinit.net.get_devicelist')
     @mock.patch('cloudinit.net.device_driver')
     @mock.patch('cloudinit.net.generate_fallback_config')
+    def test_imds_network_ignored_when_apply_network_config_false(
+            self, mock_fallback, mock_dd, mock_devlist, mock_get_mac):
+        """When apply_network_config is False, use fallback instead of IMDS."""
+        sys_cfg = {'datasource': {'Azure': {'apply_network_config': False}}}
+        odata = {'HostName': "myhost", 'UserName': "myuser"}
+        data = {'ovfcontent': construct_valid_ovf_env(data=odata),
+                'sys_cfg': sys_cfg}
+        fallback_config = {
+            'version': 1,
+            'config': [{
+                'type': 'physical', 'name': 'eth0',
+                'mac_address': '00:11:22:33:44:55',
+                'params': {'driver': 'hv_netsvc'},
+                'subnets': [{'type': 'dhcp'}],
+            }]
+        }
+        mock_fallback.return_value = fallback_config
+
+        mock_devlist.return_value = ['eth0']
+        mock_dd.return_value = ['hv_netsvc']
+        mock_get_mac.return_value = '00:11:22:33:44:55'
+
+        dsrc = self._get_ds(data)
+        self.assertTrue(dsrc.get_data())
+        self.assertEqual(dsrc.network_config, fallback_config)
+
+    @mock.patch('cloudinit.net.get_interface_mac')
+    @mock.patch('cloudinit.net.get_devicelist')
+    @mock.patch('cloudinit.net.device_driver')
+    @mock.patch('cloudinit.net.generate_fallback_config')
     def test_fallback_network_config(self, mock_fallback, mock_dd,
                                      mock_devlist, mock_get_mac):
         """On absent IMDS network data, generate network fallback config."""