Merge pull request #685 from shane-js/patch-1

Update aws-properties-rds-security-group.md - Note Move to AWS::EC2::…

Author: rachfop

doc_source/aws-properties-rds-security-group.md

@@ -2,7 +2,10 @@
 
 The `AWS::RDS::DBSecurityGroup` resource creates or updates an Amazon RDS DB security group\.
 
-**Note**  
+**Note**
+
+DB security groups are a part of the EC2-Classic Platform and as such are not supported in all regions. It is advised to use the `AWS::EC2::SecurityGroup` resource in those regions instead. To determine which platform you are on, see [Determining Whether You Are Using the EC2\-VPC or EC2\-Classic Platform](https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_VPC.FindDefaultVPC.html)\. For more information on the `AWS::EC2::SecurityGroup`, see the documentation for [EC2 security groups](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-security-group.html).
+
  If you use DB security groups, the settings that you can specify for your DB instances are limited\. For more information, see the [DBSecurityGroups](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-rds-database-instance.html#cfn-rds-dbinstance-dbsecuritygroups) property of the `AWS::RDS::DBInstance` resource\.  
  When you specify an `AWS::RDS::DBSecurityGroup` as an argument to the `Ref` function, AWS CloudFormation returns the value of the `DBSecurityGroupName`\.
 
@@ -180,4 +183,4 @@ DBSecurityGroup:
         EC2SecurityGroupName: 
           Ref: "WebServerSecurityGroup"
     GroupDescription: "Frontend Access"
-```
+```