Existing SecurityGroups can be updated using SecurityGroupIngress

For example:

 "SecurityGroupRedisIngress": {   "Type": "AWS::EC2::SecurityGroupIngress",   "Properties" :  {   "GroupId": "sg-123456789",   "IpProtocol": "tcp",   "FromPort": "6379",   "ToPort": "6379",   "CidrIp": "1.2.3.4/0"   }   }, 

Existing SecurityGroups can be updated using SecurityGroupIngress

For example:

"SecurityGroupRedisIngress": { "Type": "AWS::EC2::SecurityGroupIngress", "Properties" : { "GroupId": "sg-123456789", "IpProtocol": "tcp", "FromPort": "6379", "ToPort": "6379", "CidrIp": "1.2.3.4/0" } }