Add a model API version

This is a framework for making upgrades to the ZooKeeper data model
in a manner that can support a rolling Zuul system upgrade.

Change-Id: Iff09c95878420e19234908c2a937e9444832a6ec

1 files changed, 14 insertions, 3 deletions

diff --git a/zuul/zk/zkobject.py b/zuul/zk/zkobject.py
index e19c67982..196533889 100644
--- a/zuul/zk/zkobject.py
+++ b/zuul/zk/zkobject.py
@@ -22,19 +22,25 @@ from kazoo.exceptions import (
 
 from zuul.zk import sharding
 from zuul.zk.exceptions import InvalidObjectError
+from zuul import model
 
 
 class ZKContext:
-    def __init__(self, zk_client, lock, stop_event, log):
+    def __init__(self, zk_client, lock, stop_event, log, registry):
         self.client = zk_client.client
         self.lock = lock
         self.stop_event = stop_event
         self.log = log
+        self.registry = registry
 
     def sessionIsValid(self):
         return ((not self.lock or self.lock.is_still_valid()) and
                 (not self.stop_event or not self.stop_event.is_set()))
 
+    @property
+    def model_api(self):
+        return self.registry.model_api
+
 
 class LocalZKContext:
     """A Local ZKContext that means don't actually write anything to ZK"""
@@ -44,10 +50,15 @@ class LocalZKContext:
         self.lock = None
         self.stop_event = None
         self.log = log
+        self.registry = None
 
     def sessionIsValid(self):
         return True
 
+    @property
+    def model_api(self):
+        return model.MODEL_API
+
 
 class ZKObject:
     _retry_interval = 5
@@ -60,7 +71,7 @@ class ZKObject:
         """
         raise NotImplementedError()
 
-    def serialize(self):
+    def serialize(self, context):
         """Implement this method to return the data to save in ZK.
 
         :returns: A byte string
@@ -154,7 +165,7 @@ class ZKObject:
         if isinstance(context, LocalZKContext):
             return b''
         try:
-            return self.serialize()
+            return self.serialize(context)
         except Exception:
             # A higher level must handle this exception, but log
             # ourself here so we know what object triggered it.