DeploymentName:
    Type: String
    Description: A name for this deployment

A deployment is a deployed application, potentially comprised of many CloudFormation stacks. This is sometimes called an "environment", but that is an overloaded and confusing term. Use the DeploymentName to indicate which logical deployment a stack belongs to.

If a deployment is completely specified by exactly one CloudFormation template, the DeploymentName and the AWS::StackName refer to the same things. In that case, consider not using a DeploymentName parameter.

  KeyName:
    Type: AWS::EC2::KeyPair::KeyName
    Description: The name of an EC2 KeyPair
    Default: test

AWS does not provide a CloudFormation type for EC2 KeyPairs. This is a deliberate choice: a KeyPair consists of a public and private key, and AWS does not want to expose the private key in CloudFormation outputs.

This is one example where Terraform has an advantage: since Terraform runs locally, it can create a KeyPair and save the private key locally.

In CloudFormation, you have two options:

1. Create the KeyPair beforehand, then provide the KeyName to your CloudFormation template as a parameter.
2. Create the KeyPair using a CloudFormation Custom Resource (i.e. a Lambda Function) defined in your CloudFormation template. The Custom Resource must save the private key somewhere (like SecretsManager or SSM Parameter Store).

  SSHCIDR:
    Type: String
    Description: IP CIDR range

Allow SSH access from this CIDR range.