Flag to preserve minion cache on key delete

Refs #15673

conf/master

@@ -140,6 +140,14 @@
 # 'aes_key_rotate' event with the 'key' tag and acting appropriately.
 # ping_on_rotate: False
 
+# By default, the master deletes its cache of minion data when the key for that
+# minion is removed. To preserve the cache after key deletion, set 
+# 'preserve_minion_cache' to True.
+#
+# WARNING: This may have security implications if compromised minions auth with
+# a previous deleted minion ID.
+#preserve_minion_cache: False
+
 # If max_minions is used in large installations, the master might experience
 # high-load situations because of having to check the number of connected
 # minions for every authentication. This cache provides the minion-ids of

salt/config.py

@@ -186,6 +186,7 @@ VALID_OPTS = {
     'pillar_source_merging_strategy': str,
     'ping_on_key_rotate': bool,
     'peer': dict,
+    'preserve_minion_cache': bool,
     'syndic_master': str,
     'runner_dirs': list,
     'client_acl': dict,
@@ -474,6 +475,7 @@ DEFAULT_MASTER_OPTS = {
     'pillar_source_merging_strategy': 'smart',
     'ping_on_key_rotate': False,
     'peer': {},
+    'preserve_minion_cache': False,
     'syndic_master': '',
     'runner_dirs': [],
     'outputter_dirs': [],

salt/key.py

@@ -485,9 +485,10 @@ class Key(object):
         minions = []
         for key, val in keys.items():
             minions.extend(val)
-        for minion in os.listdir(m_cache):
-            if minion not in minions:
-                shutil.rmtree(os.path.join(m_cache, minion))
+        if self.opts.get('preserve_minion_cache', False):
+            for minion in os.listdir(m_cache):
+                if minion not in minions:
+                    shutil.rmtree(os.path.join(m_cache, minion))
 
     def check_master(self):
         '''