Add an example of watch recovery using resource_version and bookmarks

Author: anvilpete

examples/watch/watch_recovery.py

@@ -0,0 +1,78 @@
+# Copyright 2025 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Uses watch to print a stream of Pod events from the default namespace.
+The allow_watch_bookmarks flag is set to True, so the API server can send
+BOOKMARK events.
+
+If the connection to the API server is lost, the script will reconnect and 
+resume watching from the most recently received resource version.
+
+For more information, see:
+- https://kubernetes.io/docs/reference/using-api/api-concepts/#efficient-detection-of-changes
+- https://kubernetes.io/docs/reference/using-api/api-concepts/#semantics-for-watch
+"""
+
+import urllib3
+
+from kubernetes import config
+from kubernetes.client import api_client
+from kubernetes.client.exceptions import ApiException
+from kubernetes.dynamic.client import DynamicClient
+
+NAMESPACE = "default"
+
+
+def main():
+    # Configs can be set in Configuration class directly or using helper
+    # utility. If no argument provided, the config will be loaded from
+    # default location.
+    config.load_kube_config()
+    client = DynamicClient(api_client.ApiClient())
+    api = client.resources.get(api_version="v1", kind="Pod")
+    
+    # Setting resource_version=None means the server will send synthetic
+    # ADDED events for all resources that exist when the watch starts.
+    resource_version = None
+    while True:
+        try:
+            for event in api.watch(
+                namespace=NAMESPACE,
+                resource_version=resource_version,
+                allow_watch_bookmarks=True,
+            ):
+                # Remember the last resourceVersion we saw, so we can resume
+                # watching from there if the connection is lost.
+                resource_version = event['object'].metadata.resourceVersion
+
+                print("Event: %s %s %s" % (
+                    resource_version,
+                    event['type'],
+                    event['object'].metadata.name,
+                ))
+
+        except ApiException as err:
+            if err.status == 410:
+                print("ERROR: The requested resource version is no longer available.")
+                resource_version = None
+            else:
+                raise
+
+        except urllib3.exceptions.ProtocolError:
+            print("Lost connection to the k8s API server. Reconnecting...")
+
+
+if __name__ == "__main__":
+    main()