kube_uptime: No Pydantic for deserialization

Due to import times, avoid using Pydantic in places where we have a
`parsed_section_name` referencing a non-Kube section, as we do in
`kube_uptime`.

CMK-29703

Change-Id: Ia32bb67fafe57905ae8baaeb2a5819589935ba5f

Author: relrod

packages/cmk-plugins/cmk/plugins/kube/agent_based/kube_uptime.py

@@ -4,18 +4,24 @@
 # conditions defined in the file COPYING, which is part of this source code package.
 
 
+import json
 import time
-from json import loads
 
 from cmk.agent_based.v2 import AgentSection, StringTable
-from cmk.plugins.kube.schemata.section import StartTime
 from cmk.plugins.lib.uptime import Section
 
 
 def _parse_kube_start_time(now: float, string_table: StringTable) -> Section | None:
     if not string_table:
         return None
-    return Section(uptime_sec=now - StartTime(**loads(string_table[0][0])).start_time, message=None)
+
+    # We parse this manually (without using the Pydantic model) intentionally.
+    # Since we have parsed_section_name="uptime" in the AgentSection, this file
+    # gets imported/evaluated - particularly with the nagios core - for every
+    # host that has an uptime service. And importing the Pydantic models is
+    # slow. Don't use this as a good pattern to follow in the Kube plugins.
+    start_time = json.loads(string_table[0][0])["start_time"]
+    return Section(uptime_sec=now - start_time, message=None)
 
 
 def parse_kube_start_time(string_table: StringTable) -> Section | None:

packages/cmk-plugins/cmk/plugins/kube/schemata/section.py

@@ -598,7 +598,12 @@ class CollectorDaemons(Section):
 
 
 class StartTime(Section):
-    """section: kube_start_time_v1"""
+    """section: kube_start_time_v1
+
+    Note that for performance reasons (to avoid dragging in pydantic on *every*
+    host that has an uptime service), we only use this as a serializer, and we
+    deserialize the JSON manually in kube_uptime, without using Pydantic.
+    """
 
     start_time: api.Timestamp
 

packages/cmk-plugins/tests/cmk/plugins/kube/agent_based/test_kube_uptime.py

@@ -5,10 +5,19 @@
 
 
 from cmk.plugins.kube.agent_based.kube_uptime import _parse_kube_start_time
+from cmk.plugins.kube.schemata.api import Timestamp
+from cmk.plugins.kube.schemata.section import StartTime
 from cmk.plugins.lib.uptime import Section
 
 
 def test_parse_kube_start_time() -> None:
     assert _parse_kube_start_time(1.0, [['{"start_time": 0}']]) == Section(
         uptime_sec=1.0, message=None
     )
+
+
+def test_parse_kube_start_time_from_section_model() -> None:
+    start_time_json = StartTime(start_time=Timestamp(20)).model_dump_json()
+    assert _parse_kube_start_time(100.0, [[start_time_json]]) == Section(
+        uptime_sec=80.0, message=None
+    )