CloudFormation

Related to CloudFormation Init

Terraform-be-like:

AWSTemplateFormatVersion – helps us to increase functionality over time by choosing needed Version
Description – must follow after AWSTemplateFormatVersion.
Metadata – many functions, can control how UI presents CF template etc.
Parameters – add fields that prompt user for more information.
Mappings – allows to create lookup tables
Conditions – do something if met.
Outputs – how outputs, std

Template are working trough stacks.
Resources in templates are Logical Resources with specific naming.
Stacks are using Logical Resources from Template to create Physical resources
When updating template, you update stack and physical resources.

Stack Create Logical – Updates Create resource
Stack Updates Logical – Updates Physical resource
Stack Delete Logical – Delete Physical resource

Templates

Templates can be non-portable usually if configured improperly. Templates can be provided with paramenters (variables..). There can be Deafult, Allowedvalues, Min&Max lenght & allowed patterns, NoEcho (good for passwords) & Type.
Decrease number of input parameters if possible (more Defaults to) for best practice for better automation.

Also pseudo-parameters which auto-populated by AWS based on the environment

Intrinsic Functions

Intrinsic function reference - AWS CloudFormation

• Ref & Fn::GetAtt - reference value from one logical resource in another.
  • Ref literally return reference information when used on a logical resource, link instance ID
    Fn:GetAtt returns the attribute of a logical resource
    
• Fn:Join & Fn::Split
  • Split string to list with a delimiter and Join is vice-versa.
    
• Fn::GetAZs & Fn::Select
  • Important thing that GetAZs returns AZs where defaul VPC has subnets, generally this configuration is untouched (no need to delete default VPC), but be ware :O
    
    
• Conditions (Fn:: IF, And, Equals, Not & Or)
• Fn::Base64 (encode text (like user data)) & Fn::Sub (substitute text)
  • Just in case, instance variable here is incorrect on purpose
    
• Fn::Cidr – helps building cidr blocks
  • Creates Cidr ranges fro subnets
    
• Later.. Fn::ImportValue, Fn::FindInMap, Fn::Transform