dynamic_inventory.patch

diff --git i/playbooks/inventory/dynamic_inventory.py w/playbooks/inventory/dynamic_inventory.py
index cb48e37..3723ffb 100755
--- i/playbooks/inventory/dynamic_inventory.py
+++ w/playbooks/inventory/dynamic_inventory.py
@@ -780,6 +780,11 @@ def _set_used_ips(user_defined_config, inventory):
                 address = host_entry.get('%s_address' % q_name)
                 if address:
                     append_if(array=USED_IPS, item=address)
+                elif not address and q_name == 'container':
+                    import pdb; pdb.set_trace()  # NOQA
+
+    with open('./used_ips.json', 'w') as fp:
+        fp.write(json.dumps(USED_IPS, indent=2, sort_keys=True))
 
 
 def _ensure_inventory_uptodate(inventory, container_skel):