Merge branch 'master' of github.com:awslabs/cfncluster

Author: Dougal Ballantyne

cloudformation/cfncluster.cfn.json

@@ -7,8 +7,8 @@
       "Type" : "String",
       "MinLength" : "1",
       "MaxLength" : "64",
-      "AllowedPattern" : "[-_ a-zA-Z0-9]*",
-      "ConstraintDescription" : "can contain only alphanumeric characters, spaces, dashes and underscores."
+      "AllowedPattern" : "[-+_.@ a-zA-Z0-9]+",
+      "ConstraintDescription" : "can contain only alphanumeric characters, spaces, dashes, plusses, underscores, dots, and at signs."
     },
     "MasterInstanceType" : {
       "Description" : "Master Server EC2 instance type",