Resources

Resources are your actual pieces of AWS infrastructure. These are your EC2 instances, S3 buckets, ELBs, and so on. Almost any resource type you can create by pointing and clicking in the AWS web console can also be created using CloudFormation.

There are a few important things to keep in mind about CloudFormation resources:

• New or bleeding-edge AWS resources are often not immediately supported. CloudFormation support typically lags a few weeks (sometimes months) behind the release of new AWS features. This used to be quite frustrating for anyone to whom infrastructure automation is key. Fast-forward to today, and this situation is somewhat mitigated by the ability to use custom resources. These are discussed further on in this chapter.
• Resources have a default return value. You can use Ref to fetch these return values for use elsewhere in your template. For example, the AWS::EC2::VPC resource type has a default return value that is the ID of the VPC. They look something like this: vpc-11aa111a.
• Resources often contain additional return values. These additional values are fetched using the inbuilt Fn::GetAtt function. Continuing from the previous example, the AWS::EC2::VPC resource type also returns the following:
  • CidrBlock
  • DefaultNetworkAcl
  • DefaultSecurityGroup
  • Ipv6CidrBlocks