Merge pull request #347 from bundlewrap/node-magic-number

Node magic number

bundlewrap/node.py

@@ -2,6 +2,7 @@
 from __future__ import unicode_literals
 
 from datetime import datetime, timedelta
+from hashlib import md5
 from os import environ
 from sys import exit
 from threading import Lock
@@ -526,6 +527,10 @@ def items(self):
                 for item in bundle.items:
                     yield item
 
+    @cached_property
+    def magic_number(self):
+        return int(md5(self.name.encode('UTF-8')).hexdigest(), 16)
+
     @property
     def _static_items(self):
         for bundle in self.bundles:

docs/content/repo/nodes.py.md

@@ -71,6 +71,16 @@ A string used as a DNS name when connecting to this node. May also be an IP addr
 Cannot be set at group level.
 
 
+### magic_number
+
+A large number derived from the node's name. This number is very likely to be unique for your entire repository. You can, for example, use this number to easily "jitter" cronjobs:
+
+    '{} {} * * * root /my/script'.format(
+        node.magic_number % 60,
+        node.magic_number % 2 + 4,
+    )
+
+
 ### metadata
 
 This can be a dictionary of arbitrary data (some type restrictions apply). You can access it from your templates as `node.metadata`. Use this to attach custom data (such as a list of IP addresses that should be configured on the target node) to the node. Note that you can also define metadata at the [group level](groups.py.md#metadata), but node metadata has higher priority.