A designer is preparing for a demo to the development lead. He is using a Cloudformation template as the template could be version controlled. He wants the template to be able to get the SSH Key as a user input in order to SSH to an EC2 instance that will be created by the Cloudformation stack later on. Which below approach is the proper one to make this happen?

Answer options:

A.Design the template using XML format and add a parameter as the SSH Key. Refer to this parameter for new EC2 instances.
B.Use an editor to write a template using JSON or YAML. Add a parameter section for the SSH Key such as “MyKeyPair”. For new instances, use the keyword of “Ref” to use this parameter. Save the template in S3 and upload it during stack creation.
C.In the template editor that has been provided by AWS, design the template using JSON or YAML. Add a parameter for the SSH Key such as “MyKeyPair”. For new instances, use the keyword “Reference” to link to the “key” parameter.
D.Design the template using XML format. Add a parameter called “MyKeyPair” with the “Type” as “Key”. For new EC2 instances, use the keyword of “Ref” to refer to this parameter in the Metadata section. Save the template in a S3 and refer to the S3 link during stack creation.

Corrrect Answer: B
You can author AWS CloudFormation templates in JSON or YAML formats.
The optional Parameters section is used to customize your templates. Parameters enable you to input custom values to your template each time you create or update a stack.
You use the Ref intrinsic function to reference a parameter, and AWS CloudFormation uses the parameter`s value to provision the stack. You can reference parameters from the Resources and Outputs sections of the same template.
The below is an example of using “MyKeyPair” as a parameter:
Option A is incorrect: because XML cannot be used for Cloudformation template.
Option C is incorrect: because the keyword to refer to parameter is “Ref” rather than “Reference”.
Option D is incorrect: because for Parameter, the type should be a string for this case. The type of “Key” is wrong. XML also cannot be used for Cloudformation template.
Please refer to https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/parameters-section-structure.html for the structure of parameter section. Other than that, to use the parameter for instances, the “Ref” should be put into “Properties” section rather than “Metadata”.