cloud-id: better handling of change in datasource files

Stop deleting cloud-id-<cloudname> unless there is a change in
discovered datasource cloud-id.

LP: #1998998

3 files changed, 31 insertions, 7 deletions

diff --git a/cloudinit/sources/__init__.py b/cloudinit/sources/__init__.py
index 85e094ac..12430401 100644
--- a/cloudinit/sources/__init__.py
+++ b/cloudinit/sources/__init__.py
@@ -435,12 +435,15 @@ class DataSource(CloudInitPickleMixin, metaclass=abc.ABCMeta):
         cloud_id = instance_data["v1"].get("cloud_id", "none")
         cloud_id_file = os.path.join(self.paths.run_dir, "cloud-id")
         util.write_file(f"{cloud_id_file}-{cloud_id}", f"{cloud_id}\n")
+        # cloud-id not found, then no previous cloud-id fle
+        prev_cloud_id_file = None
+        new_cloud_id_file = f"{cloud_id_file}-{cloud_id}"
+        # cloud-id found, then the prev cloud-id file is source of symlink
         if os.path.exists(cloud_id_file):
             prev_cloud_id_file = os.path.realpath(cloud_id_file)
-        else:
-            prev_cloud_id_file = cloud_id_file
-        util.sym_link(f"{cloud_id_file}-{cloud_id}", cloud_id_file, force=True)
-        if prev_cloud_id_file != cloud_id_file:
+
+        util.sym_link(new_cloud_id_file, cloud_id_file, force=True)
+        if prev_cloud_id_file and prev_cloud_id_file != new_cloud_id_file:
             util.del_file(prev_cloud_id_file)
         write_json(json_sensitive_file, processed_data, mode=0o600)
         json_file = self.paths.get_runpath("instance_data")
diff --git a/tests/integration_tests/modules/test_combined.py b/tests/integration_tests/modules/test_combined.py
index 3c1013eb..647e8728 100644
--- a/tests/integration_tests/modules/test_combined.py
+++ b/tests/integration_tests/modules/test_combined.py
@@ -424,6 +424,23 @@ class TestCombined:
         assert v1_data["instance_id"] == client.instance.instance_id
         assert v1_data["local_hostname"] == client.instance.name
 
+    @pytest.mark.lxd_container
+    @pytest.mark.azure
+    @pytest.mark.gce
+    @pytest.mark.ec2
+    def test_instance_cloud_id_across_reboot(
+        self, class_client: IntegrationInstance
+    ):
+        client = class_client
+        platform = client.settings.PLATFORM
+        cloud_id_alias = {"ec2": "aws", "lxd_container": "lxd"}
+        cloud_file = f"cloud-id-{cloud_id_alias.get(platform, platform)}"
+        assert client.execute(f"test -f /run/cloud-init/{cloud_file}").ok
+        assert client.execute("test -f /run/cloud-init/cloud-id").ok
+        client.restart()
+        assert client.execute(f"test -f /run/cloud-init/{cloud_file}").ok
+        assert client.execute("test -f /run/cloud-init/cloud-id").ok
+
 
 @pytest.mark.user_data(USER_DATA)
 class TestCombinedNoCI:
diff --git a/tests/unittests/sources/test_init.py b/tests/unittests/sources/test_init.py
index a81c33a2..0447e02c 100644
--- a/tests/unittests/sources/test_init.py
+++ b/tests/unittests/sources/test_init.py
@@ -716,9 +716,13 @@ class TestDataSource(CiTestCase):
             "cloudinit.sources.canonical_cloud_id", return_value="my-cloud"
         ):
             datasource.get_data()
-        self.assertEqual("my-cloud\n", util.load_file(cloud_id_link))
-        # A symlink with the generic /run/cloud-init/cloud-id link is present
-        self.assertTrue(util.is_link(cloud_id_link))
+            self.assertEqual("my-cloud\n", util.load_file(cloud_id_link))
+            # A symlink with the generic /run/cloud-init/cloud-id
+            # link is present
+            self.assertTrue(util.is_link(cloud_id_link))
+            datasource.persist_instance_data()
+            # cloud-id<cloud-type> not deleted: no cloud-id change
+            self.assertTrue(os.path.exists(cloud_id_file))
         # When cloud-id changes, symlink and content change
         with mock.patch(
             "cloudinit.sources.canonical_cloud_id", return_value="my-cloud2"