Update ironic driver get_available_nodes docstring

This was out of date, it now returns a subset of Ironic nodes.

Change-Id: I7e0bdd2578e1c32dbb0d607b1355be7be45501df

diff --git a/nova/virt/ironic/driver.py b/nova/virt/ironic/driver.py
index 0d828ed6a8b00e3b4b68318e386aed2b8931bec3..dfcd067240a3c1323ce931d35c92e30e61c2e7be 100644 (file)
--- a/nova/virt/ironic/driver.py
+++ b/nova/virt/ironic/driver.py
@@ -578,7 +578,20 @@ class IronicDriver(virt_driver.ComputeDriver):
         self.node_cache_time = time.time()
 
     def get_available_nodes(self, refresh=False):
-        """Returns the UUIDs of all nodes in the Ironic inventory.
+        """Returns the UUIDs of Ironic nodes managed by this compute service.
+
+        We use consistent hashing to distribute Ironic nodes between all
+        available compute services. The subset of nodes managed by a given
+        compute service is determined by the following rules:
+
+        * any node with an instance managed by the compute service
+        * any node that is mapped to the compute service on the hash ring
+        * no nodes with instances managed by another compute service
+
+        The ring is rebalanced as nova-compute services are brought up and
+        down. Note that this rebalance does not happen at the same time for
+        all compute services, so a node may be managed by multiple compute
+        services for a small amount of time.
 
         :param refresh: Boolean value; If True run update first. Ignored by
                         this driver.