Azure: Support for VMs without ephemeral resource disks. (#800)

Changes:
* Only merge in default Azure cloud ephemeral disk configs
during DataSourceAzure._get_data() if the ephemeral disk
exists.
* DataSourceAzure.address_ephemeral_resize() (which is
invoked in DataSourceAzure.activate() should only set up
the ephemeral disk if the disk exists.

Azure VMs may or may not come with ephemeral resource disks
depending on the VM SKU. For VM SKUs that come with
ephemeral resource disks, the Azure platform guarantees that
the ephemeral resource disk is attached to the VM before
the VM is booted. For VM SKUs that do not come with
ephemeral resource disks, cloud-init currently attempts
to wait and set up a non-existent ephemeral resource
disk, which wastes boot time. It also causes disk setup
modules to fail (due to non-existent references to the
ephemeral resource disk).

udevadm settle is invoked by cloud-init very early in boot.
udevadm settle is invoked very early, before
DataSourceAzure's _get_data() and activate() methods.

Within DataSourceAzure's _get_data() and activate() methods,
the ephemeral resource disk path should exist if the
VM SKU comes with an ephemeral resource disk.
The ephemeral resource disk path should not exist if the
VM SKU does not come with an ephemeral resource disk.

LP: #1901011

cloudinit/sources/DataSourceAzure.py

@@ -270,7 +270,7 @@ def get_resource_disk_on_freebsd(port_id):
 }
 # RELEASE_BLOCKER: Xenial and earlier apply_network_config default is False
 
-BUILTIN_CLOUD_CONFIG = {
+BUILTIN_CLOUD_EPHEMERAL_DISK_CONFIG = {
     'disk_setup': {
         'ephemeral0': {'table_type': 'gpt',
                        'layout': [100],
@@ -618,8 +618,26 @@ def _get_data(self):
             maybe_remove_ubuntu_network_config_scripts()
 
         # Process crawled data and augment with various config defaults
-        self.cfg = util.mergemanydict(
-            [crawled_data['cfg'], BUILTIN_CLOUD_CONFIG])
+
+        # Only merge in default cloud config related to the ephemeral disk
+        # if the ephemeral disk exists
+        devpath = RESOURCE_DISK_PATH
+        if os.path.exists(devpath):
+            report_diagnostic_event(
+                "Ephemeral resource disk '%s' exists. "
+                "Merging default Azure cloud ephemeral disk configs."
+                % devpath,
+                logger_func=LOG.debug)
+            self.cfg = util.mergemanydict(
+                [crawled_data['cfg'], BUILTIN_CLOUD_EPHEMERAL_DISK_CONFIG])
+        else:
+            report_diagnostic_event(
+                "Ephemeral resource disk '%s' does not exist. "
+                "Not merging default Azure cloud ephemeral disk configs."
+                % devpath,
+                logger_func=LOG.debug)
+            self.cfg = crawled_data['cfg']
+
         self._metadata_imds = crawled_data['metadata']['imds']
         self.metadata = util.mergemanydict(
             [crawled_data['metadata'], DEFAULT_METADATA])
@@ -1468,26 +1486,17 @@ def count_files(mp):
 
 
 @azure_ds_telemetry_reporter
-def address_ephemeral_resize(devpath=RESOURCE_DISK_PATH, maxwait=120,
+def address_ephemeral_resize(devpath=RESOURCE_DISK_PATH,
                              is_new_instance=False, preserve_ntfs=False):
-    # wait for ephemeral disk to come up
-    naplen = .2
-    with events.ReportEventStack(
-        name="wait-for-ephemeral-disk",
-        description="wait for ephemeral disk",
-        parent=azure_ds_reporter
-    ):
-        missing = util.wait_for_files([devpath],
-                                      maxwait=maxwait,
-                                      naplen=naplen,
-                                      log_pre="Azure ephemeral disk: ")
-
-        if missing:
-            report_diagnostic_event(
-                "ephemeral device '%s' did not appear after %d seconds." %
-                (devpath, maxwait),
-                logger_func=LOG.warning)
-            return
+    if not os.path.exists(devpath):
+        report_diagnostic_event(
+            "Ephemeral resource disk '%s' does not exist." % devpath,
+            logger_func=LOG.debug)
+        return
+    else:
+        report_diagnostic_event(
+            "Ephemeral resource disk '%s' exists." % devpath,
+            logger_func=LOG.debug)
 
     result = False
     msg = None

integration-requirements.txt

@@ -1,5 +1,5 @@
 # PyPI requirements for cloud-init integration testing
 # https://cloudinit.readthedocs.io/en/latest/topics/integration_tests.html
 #
-pycloudlib @ git+https://github.com/canonical/pycloudlib.git@3a6c668fed769f00d83d1e6bea7d68953787cc38
+pycloudlib @ git+https://github.com/canonical/pycloudlib.git@da8445325875674394ffd85aaefaa3d2d0e0020d
 pytest

tests/integration_tests/bugs/test_lp1901011.py

@@ -0,0 +1,58 @@
+"""Integration test for LP: #1901011
+
+Ensure an ephemeral disk exists after boot.
+
+See https://github.com/canonical/cloud-init/pull/800
+"""
+import pytest
+
+from tests.integration_tests.clouds import IntegrationCloud
+
+
+@pytest.mark.azure
+@pytest.mark.parametrize('instance_type,is_ephemeral', [
+    ('Standard_DS1_v2', True),
+    ('Standard_D2s_v4', False),
+])
+def test_ephemeral(instance_type, is_ephemeral,
+                   session_cloud: IntegrationCloud, setup_image):
+    if is_ephemeral:
+        expected_log = (
+            "Ephemeral resource disk '/dev/disk/cloud/azure_resource' exists. "
+            "Merging default Azure cloud ephemeral disk configs."
+        )
+    else:
+        expected_log = (
+            "Ephemeral resource disk '/dev/disk/cloud/azure_resource' does "
+            "not exist. Not merging default Azure cloud ephemeral disk "
+            "configs."
+        )
+
+    with session_cloud.launch(
+        launch_kwargs={'instance_type': instance_type}
+    ) as client:
+        # Verify log file
+        log = client.read_from_file('/var/log/cloud-init.log')
+        assert expected_log in log
+
+        # Verify devices
+        dev_links = client.execute('ls /dev/disk/cloud')
+        assert 'azure_root' in dev_links
+        assert 'azure_root-part1' in dev_links
+        if is_ephemeral:
+            assert 'azure_resource' in dev_links
+            assert 'azure_resource-part1' in dev_links
+
+        # Verify mounts
+        blks = client.execute('lsblk -pPo NAME,TYPE,MOUNTPOINT')
+        root_device = client.execute(
+            'realpath /dev/disk/cloud/azure_root-part1'
+        )
+        assert 'NAME="{}" TYPE="part" MOUNTPOINT="/"'.format(
+            root_device) in blks
+        if is_ephemeral:
+            ephemeral_device = client.execute(
+                'realpath /dev/disk/cloud/azure_resource-part1'
+            )
+            assert 'NAME="{}" TYPE="part" MOUNTPOINT="/mnt"'.format(
+                ephemeral_device) in blks

tests/unittests/test_datasource/test_azure.py

@@ -1354,23 +1354,51 @@ def test_cfg_has_no_fingerprint_has_value(self):
         for mypk in mypklist:
             self.assertIn(mypk['value'], dsrc.metadata['public-keys'])
 
-    def test_default_ephemeral(self):
-        # make sure the ephemeral device works
+    def test_default_ephemeral_configs_ephemeral_exists(self):
+        # make sure the ephemeral configs are correct if disk present
         odata = {}
         data = {'ovfcontent': construct_valid_ovf_env(data=odata),
                 'sys_cfg': {}}
 
-        dsrc = self._get_ds(data)
-        ret = dsrc.get_data()
-        self.assertTrue(ret)
-        cfg = dsrc.get_config_obj()
+        orig_exists = dsaz.os.path.exists
+
+        def changed_exists(path):
+            return True if path == dsaz.RESOURCE_DISK_PATH else orig_exists(
+                path)
+
+        with mock.patch(MOCKPATH + 'os.path.exists', new=changed_exists):
+            dsrc = self._get_ds(data)
+            ret = dsrc.get_data()
+            self.assertTrue(ret)
+            cfg = dsrc.get_config_obj()
+
+            self.assertEqual(dsrc.device_name_to_device("ephemeral0"),
+                             dsaz.RESOURCE_DISK_PATH)
+            assert 'disk_setup' in cfg
+            assert 'fs_setup' in cfg
+            self.assertIsInstance(cfg['disk_setup'], dict)
+            self.assertIsInstance(cfg['fs_setup'], list)
+
+    def test_default_ephemeral_configs_ephemeral_does_not_exist(self):
+        # make sure the ephemeral configs are correct if disk not present
+        odata = {}
+        data = {'ovfcontent': construct_valid_ovf_env(data=odata),
+                'sys_cfg': {}}
+
+        orig_exists = dsaz.os.path.exists
+
+        def changed_exists(path):
+            return False if path == dsaz.RESOURCE_DISK_PATH else orig_exists(
+                path)
+
+        with mock.patch(MOCKPATH + 'os.path.exists', new=changed_exists):
+            dsrc = self._get_ds(data)
+            ret = dsrc.get_data()
+            self.assertTrue(ret)
+            cfg = dsrc.get_config_obj()
 
-        self.assertEqual(dsrc.device_name_to_device("ephemeral0"),
-                         dsaz.RESOURCE_DISK_PATH)
-        assert 'disk_setup' in cfg
-        assert 'fs_setup' in cfg
-        self.assertIsInstance(cfg['disk_setup'], dict)
-        self.assertIsInstance(cfg['fs_setup'], list)
+            assert 'disk_setup' not in cfg
+            assert 'fs_setup' not in cfg
 
     def test_provide_disk_aliases(self):
         # Make sure that user can affect disk aliases