CloudFormation

Building Blocks

Resources: AWS resources declared in the template (can use !Ref function to refer to others resources in the same YAML file)
Parameters: the dynamic inputs (use with !Ref function)
Mappings: the static variables (use with !FindInMap[ MapName, TopLevelKey, SecondLevelKey ] function)
Outputs: export to be used by other stacks (other stacks use !ImportValue function to reference). Exported output names must be unique within region
Conditionals: List of conditions to perform resource creation (!If, !Not, !Equal...)
Metadata

Stack Creation Fails:
- Default: everything rolls back (gets deleted)
- Option to disable rollback and troubleshoot what happened
Stack Update Fails:
- The stack automatically rolls back to the previous known working state
- Ability to see in the log what happened and error messages

Can I create a dynamic amount of resources?
- No, you can't. Everything in CloudFormation templates has to be declared. Can't perform code generation here
Is every AWS Service supported in CloudFormation's resources?
- Almost. Only a select few niches are not there yet
- You can work around that using AWS Lambda Custom Resources
Exported output names must be unique within region
!GetAtt
!Join
- want to create "a:b:c" ⇒ !Join [ ":", [a, b, c] ]

!Sub

with a Mapping

  Name: !Sub
    - www.${Domain}
    - { Domain: !Ref RootDomainName }

without a Mapping

  !Sub 'arn:aws:ec2:${AWS::Region}:${AWS::AccountId}:vpc/${vpc}'