add support Lease-based leader election (rather than ConfigMaps) #1877

Signed-off-by: Lane Richard <rick.lane@nokia.com>

kubernetes/base/leaderelection/example.py

@@ -16,6 +16,7 @@
 from kubernetes import client, config
 from kubernetes.leaderelection import leaderelection
 from kubernetes.leaderelection.resourcelock.configmaplock import ConfigMapLock
+from kubernetes.leaderelection.resourcelock.leaselock import LeaseLock
 from kubernetes.leaderelection import electionconfig
 
 
@@ -42,10 +43,13 @@ def example_func():
 # A user can choose not to provide any callbacks for what to do when a candidate fails to lead - onStoppedLeading()
 # In that case, a default callback function will be used
 
+# Choose the type of lock mechanism to use
+lock_object = LeaseLock(lock_name, lock_namespace, candidate_id)
+#lock_object = ConfigMapLock(lock_name, lock_namespace, candidate_id)
+
 # Create config
-config = electionconfig.Config(ConfigMapLock(lock_name, lock_namespace, candidate_id), lease_duration=17,
-                               renew_deadline=15, retry_period=5, onstarted_leading=example_func,
-                               onstopped_leading=None)
+config = electionconfig.Config(lock_object, lease_duration=17, renew_deadline=15, retry_period=5,
+                               onstarted_leading=example_func, onstopped_leading=None)
 
 # Enter leader election
 leaderelection.LeaderElection(config).run()

kubernetes/base/leaderelection/leaderelectionrecord.py

@@ -14,7 +14,7 @@
 
 
 class LeaderElectionRecord:
-    # Annotation used in the lock object
+    # Lease configuration from in the lock object.
     def __init__(self, holder_identity, lease_duration, acquire_time, renew_time):
         self.holder_identity = holder_identity
         self.lease_duration = lease_duration

kubernetes/base/leaderelection/resourcelock/configmaplock.py

@@ -13,8 +13,7 @@
 # limitations under the License.
 
 from kubernetes.client.rest import ApiException
-from kubernetes import client, config
-from kubernetes.client.api_client import ApiClient
+from kubernetes import client
 from ..leaderelectionrecord import LeaderElectionRecord
 import json
 import logging
@@ -126,4 +125,4 @@ def get_lock_dict(self, leader_election_record):
         self.lock_record['acquireTime'] = leader_election_record.acquire_time
         self.lock_record['renewTime'] = leader_election_record.renew_time
 
-        return self.lock_record
+        return self.lock_record

kubernetes/base/leaderelection/resourcelock/leaselock.py

@@ -0,0 +1,129 @@
+# Copyright 2021 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.
+
+from kubernetes.client.rest import ApiException
+from kubernetes import client
+from ..leaderelectionrecord import LeaderElectionRecord
+from datetime import datetime
+import logging
+logging.basicConfig(level=logging.INFO)
+
+
+class LeaseLock:
+    def __init__(self, name, namespace, identity):
+        """
+        :param name: name of the lock
+        :param namespace: namespace
+        :param identity: A unique identifier that the candidate is using
+        """
+        self.api_instance = client.CoordinationV1Api()
+
+        # lease resource identity and reference
+        self.name = name
+        self.namespace = namespace
+        self.lease_reference = None
+
+        # identity of this candidate
+        self.identity = str(identity)
+
+    # get returns the election record from a Lease Annotation
+    def get(self, name, namespace):
+        """
+        :param name: Name of the lease object information to get
+        :param namespace: Namespace in which the lease object is to be searched
+        :return: 'True, election record' if object found else 'False, exception response'
+        """
+        try:
+            lease = self.api_instance.read_namespaced_lease(name, namespace)
+
+        except ApiException as e:
+            return False, e
+        else:
+            self.lease_reference = lease
+            return True, self.election_record(lease)
+
+    def create(self, name, namespace, election_record):
+        """
+        :param electionRecord: Annotation string
+        :param name: Name of the lease object to be created
+        :param namespace: Namespace in which the lease object is to be created
+        :return: 'True' if object is created else 'False' if failed
+        """
+        body = client.V1Lease(metadata={"name": name},
+                              spec=self.update_lease(election_record))
+
+        try:
+            _ = self.api_instance.create_namespaced_lease(namespace, body, pretty=True)
+            return True
+        except ApiException as e:
+            logging.info("Failed to create lock as {}".format(e))
+            return False
+
+    def update(self, name, namespace, updated_record):
+        """
+        :param name: name of the lock to be updated
+        :param namespace: namespace the lock is in
+        :param updated_record: the updated election record
+        :return: True if update is successful False if it fails
+        """
+        try:
+            # update the Lease from the updated record
+            self.lease_reference.spec = self.update_lease(updated_record,
+                                                          self.lease_reference.spec)
+
+            _ = self.api_instance.replace_namespaced_lease(name=name, namespace=namespace,
+                                                           body=self.lease_reference)
+            return True
+        except ApiException as e:
+            logging.info("Failed to update lock as {}".format(e))
+            return False
+
+    def update_lease(self, leader_election_record, current_spec=None):
+        # existing or new lease?
+        spec = current_spec if current_spec else client.V1LeaseSpec()
+
+        # lease configuration
+        spec.holder_identity = leader_election_record.holder_identity
+        spec.lease_duration_seconds = int(leader_election_record.lease_duration)
+        spec.acquire_time = self.time_str_to_iso(leader_election_record.acquire_time)
+        spec.renew_time = self.time_str_to_iso(leader_election_record.renew_time)
+
+        return spec
+
+    def election_record(self, lease):
+        """
+        Get leader election record from Lease spec.
+        """
+        leader_election_record = LeaderElectionRecord(None, None, None, None)
+
+        if lease.spec and lease.spec.holder_identity:
+            leader_election_record.holder_identity = lease.spec.holder_identity
+        if lease.spec and lease.spec.lease_duration_seconds:
+            leader_election_record.lease_duration = str(lease.spec.lease_duration_seconds)
+        if lease.spec and lease.spec.acquire_time:
+            leader_election_record.acquire_time = str(datetime.replace(lease.spec.acquire_time, tzinfo=None))
+        if lease.spec and lease.spec.renew_time:
+            leader_election_record.renew_time = str(datetime.replace(lease.spec.renew_time, tzinfo=None))
+
+        return leader_election_record
+
+    # conversion between kubernetes ISO formatted time and elector record time 
+    def time_str_to_iso(self, str_time):
+        formats = ["%Y-%m-%d %H:%M:%S.%f%z", "%Y-%m-%d %H:%M:%S.%f"]
+        for fmt in formats:
+            try:
+                return datetime.strptime(str_time, fmt).isoformat()+'Z'
+            except ValueError:
+                pass
+        logging.error("Failed to parse time string: {}".format(str_time))