azure: fix regression introduced when persisting ephemeral dhcp lease

In commitish 9073951 azure datasource tried to leverage stale DHCP
information obtained from EphemeralDHCPv4 context manager to report
updated provisioning status to the fabric earlier in the boot process.

Unfortunately the stale ephemeral network configuration had already been
torn down in preparation to bring up IMDS network config so the report
attempt failed on timeout.

This branch introduces obtain_lease and clean_network public methods on
EphemeralDHCPv4 to allow for setup and teardown of ephemeral network
configuration without using a context manager. Azure datasource now uses
this to persist ephemeral network configuration across multiple contexts
during provisioning to avoid multiple DHCP roundtrips.

1 files changed, 28 insertions, 19 deletions

diff --git a/cloudinit/sources/DataSourceAzure.py b/cloudinit/sources/DataSourceAzure.py
index 7bdd43d8..5ec6096f 100644
--- a/cloudinit/sources/DataSourceAzure.py
+++ b/cloudinit/sources/DataSourceAzure.py
@@ -267,7 +267,6 @@ class DataSourceAzure(sources.DataSource):
     dsname = 'Azure'
     _negotiated = False
     _metadata_imds = sources.UNSET
-    lease_info = None
 
     def __init__(self, sys_cfg, distro, paths):
         sources.DataSource.__init__(self, sys_cfg, distro, paths)
@@ -281,6 +280,7 @@ class DataSourceAzure(sources.DataSource):
         self._network_config = None
         # Regenerate network config new_instance boot and every boot
         self.update_events['network'].add(EventType.BOOT)
+        self._ephemeral_dhcp_ctx = None
 
     def __str__(self):
         root = sources.DataSource.__str__(self)
@@ -407,10 +407,9 @@ class DataSourceAzure(sources.DataSource):
                 LOG.warning("%s was not mountable", cdev)
                 continue
 
-            should_report_ready_after_reprovision = False
-            if reprovision or self._should_reprovision(ret):
+            perform_reprovision = reprovision or self._should_reprovision(ret)
+            if perform_reprovision:
                 ret = self._reprovision()
-                should_report_ready_after_reprovision = True
             imds_md = get_metadata_from_imds(
                 self.fallback_interface, retries=3)
             (md, userdata_raw, cfg, files) = ret
@@ -438,9 +437,16 @@ class DataSourceAzure(sources.DataSource):
         crawled_data['metadata']['instance-id'] = util.read_dmi_data(
             'system-uuid')
 
-        if should_report_ready_after_reprovision:
+        if perform_reprovision:
             LOG.info("Reporting ready to Azure after getting ReprovisionData")
-            self._report_ready(lease=self.lease_info)
+            use_cached_ephemeral = (net.is_up(self.fallback_interface) and
+                                    getattr(self, '_ephemeral_dhcp_ctx', None))
+            if use_cached_ephemeral:
+                self._report_ready(lease=self._ephemeral_dhcp_ctx.lease)
+                self._ephemeral_dhcp_ctx.clean_network()  # Teardown ephemeral
+            else:
+                with EphemeralDHCPv4() as lease:
+                    self._report_ready(lease=lease)
 
         return crawled_data
 
@@ -529,20 +535,23 @@ class DataSourceAzure(sources.DataSource):
 
         while True:
             try:
-                with EphemeralDHCPv4() as lease:
-                    self.lease_info = lease
-                    if report_ready:
-                        path = REPORTED_READY_MARKER_FILE
-                        LOG.info(
-                            "Creating a marker file to report ready: %s", path)
-                        util.write_file(path, "{pid}: {time}\n".format(
-                            pid=os.getpid(), time=time()))
-                        self._report_ready(lease=lease)
-                        report_ready = False
-                    return readurl(url, timeout=1, headers=headers,
-                                   exception_cb=exc_cb, infinite=True,
-                                   log_req_resp=False).contents
+                # Save our EphemeralDHCPv4 context so we avoid repeated dhcp
+                self._ephemeral_dhcp_ctx = EphemeralDHCPv4()
+                lease = self._ephemeral_dhcp_ctx.obtain_lease()
+                if report_ready:
+                    path = REPORTED_READY_MARKER_FILE
+                    LOG.info(
+                        "Creating a marker file to report ready: %s", path)
+                    util.write_file(path, "{pid}: {time}\n".format(
+                        pid=os.getpid(), time=time()))
+                    self._report_ready(lease=lease)
+                    report_ready = False
+                return readurl(url, timeout=1, headers=headers,
+                               exception_cb=exc_cb, infinite=True,
+                               log_req_resp=False).contents
             except UrlError:
+                # Teardown our EphemeralDHCPv4 context on failure as we retry
+                self._ephemeral_dhcp_ctx.clean_network()
                 pass
 
     def _report_ready(self, lease):