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

1 files changed, 31 insertions, 22 deletions

diff --git a/cloudinit/sources/DataSourceAzure.py b/cloudinit/sources/DataSourceAzure.py
index 748a9716..cee630f7 100755
--- a/cloudinit/sources/DataSourceAzure.py
+++ b/cloudinit/sources/DataSourceAzure.py
@@ -270,7 +270,7 @@ BUILTIN_DS_CONFIG = {
 }
 # 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 @@ class DataSourceAzure(sources.DataSource):
             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 can_dev_be_reformatted(devpath, preserve_ntfs):
 
 
 @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