First pass at an automated check in the minion tune-in loop, using a threaded approach to periodically refresh the master if the grains on a minion have changed.

conf/minion

@@ -182,6 +182,15 @@
 # often lower this value
 #loop_interval: 60
 
+# The grains_refresh_every setting allows for a minion to periodically check
+# its grains to see if they have changed and, if so, to inform the master
+# of the new grains. This operation is moderately expensive, therefore
+# care should be taken not to set this value too low. A value of 600 seconds
+# is a reasonable place to start.
+#
+# If the value is set to zero, this check is disabled.
+grains_refresh_every = 0
+
 # When healing, a dns_check is run. This is to make sure that the originally
 # resolved dns has not changed. If this is something that does not happen in
 # your environment, set this value to False.

salt/config.py

@@ -165,6 +165,7 @@ VALID_OPTS = {
     'win_repo_mastercachefile': str,
     'win_gitrepos': list,
     'modules_max_memory': int,
+    'grains_refresh_every': int,
 }
 
 # default configurations
@@ -252,6 +253,7 @@ DEFAULT_MINION_OPTS = {
     'tcp_keepalive_cnt': -1,
     'tcp_keepalive_intvl': -1,
     'modules_max_memory': -1,
+    'grains_refresh_every': 0,
 }
 
 DEFAULT_MASTER_OPTS = {

salt/minion.py

@@ -911,6 +911,24 @@ class Minion(object):
                 data['arg'] = []
             self._handle_decoded_payload(data)
 
+    def _refresh_grains_watcher(self, refresh_interval_in_seconds):
+        '''
+        Create a loop that will fire a pillar refresh to inform a master about a change in the grains of this minion
+        :param refresh_interval_in_seconds:
+        :return: None
+        '''
+
+        def _do_refresh():
+            if grain_cache != self.opts['grains']:
+                log.debug('Grain refresh is launching Pillar refresh!')
+                self.pillar_refresh()
+
+            threading.Timer(refresh_interval_in_seconds, _do_refresh).start()
+
+        grain_cache = self.opts['grains']
+        threading.Timer(refresh_interval_in_seconds, _do_refresh).start()
+        log.debug('Starting grain refresh routine')
+
     @property
     def master_pub(self):
         '''
@@ -982,6 +1000,7 @@ class Minion(object):
     def tune_in(self):
         '''
         Lock onto the publisher. This is the main event loop for the minion
+        :rtype : None
         '''
         try:
             log.info(
@@ -1134,6 +1153,21 @@ class Minion(object):
         time.sleep(.5)
 
         loop_interval = int(self.opts['loop_interval'])
+
+        # Calculate the refresh interval for grain refresh
+        if loop_interval and self.opts['grains_refresh_every']:
+            grains_refresh_interval = self.opts['grains_refresh_every']
+            if loop_interval > grains_refresh_interval:     # We can't refresh grains more frequently
+                                                            # than we check for events
+                grains_refresh_interval = int(int(self.opts['grains_refresh_every']) / (loop_interval * 1000))
+
+        try:
+            if grains_refresh_interval:
+                self._refresh_grains_watcher(grains_refresh_interval)
+        except Exception:
+            log.error(
+                'Exception occurred in attempt to initialize grain refresh routine during minion tune-in'
+            )
         while True:
             try:
                 self.schedule.eval()