Do not filter out RDS instances by default or in INI file to avoid changing current behaviour.

plugins/inventory/ec2.ini

@@ -38,8 +38,8 @@ vpc_destination_variable = ip_address
 # Route53, uncomment and set 'route53' to True.
 route53 = False
 
-# To include RDS instances in inventory, set to True.
-rds = False
+# To exclude RDS instances from the inventory, uncomment and set to False.
+#rds = False
 
 # Additionally, you can specify the list of zones to exclude looking up in
 # 'route53_excluded_zones' as a comma-separated list.

plugins/inventory/ec2.py

@@ -223,6 +223,8 @@ class Ec2Inventory(object):
                 config.get('ec2', 'route53_excluded_zones', '').split(','))
 
         # RDS
+        self.rds_enabled = True
+        if config.has_option('ec2', 'rds'):
             self.rds_enabled = config.getboolean('ec2', 'rds')
 
         # Cache related