"Resources" : { ... "DBInstance" : { "Type": "AWS::RDS::DBInstance", "Properties": { "DBName" : { "Ref" : "DBName" }, "Engine" : "MySQL", "MasterUsername" : { "Ref" : "DBUsername" }, "DBInstanceClass" : { "Ref" : "DBClass" }, "DBSecurityGroups" : [{ "Ref" : "DBSecurityGroup" }], "AllocatedStorage" : { "Ref" : "DBAllocatedStorage" }, "MasterUserPassword": { "Ref" : "DBPassword" } } }, "DBSecurityGroup": { "Type": "AWS::RDS::DBSecurityGroup", "Properties": { "DBSecurityGroupIngress": { "EC2SecurityGroupName": { "Ref": "WebServerSecurityGroup"} }, "GroupDescription" : "Frontend Access" } }, ... },