2-IntrinsicFunctions.yaml

## =================== DESCRIPTION ===================
Description: >-
  AWS CloudFormation sample template. 
  Create a new EC2 instance and if environment is 'prod' then attach a new EBS volume to it

## =================== PARAMETERS ===================
Parameters:
  paramEnvironmentType: # ask a user to define whether it is 'dev', 'qa' or 'prod' environment
    Description: Environment type
    Default: dev # by default it is 'dev' environment
    Type: String
    AllowedValues: [dev, qa, prod]
    ConstraintDescription: Must specify 'dev', 'qa' or 'prod'
  paramTagValues: #ask a user to specify some values for tags
    Description: 'Comma-delimited list of tag values'
    Type: CommaDelimitedList
    Default: 'JonSnow, DaenerysTargaryen, AryaStark'

## =================== MAPPINGS ===================
Mappings: # map image ids with regions
  mapRegion:
    us-east-1:
      AMI: ami-1853ac65
    us-west-1:
      AMI: ami-bf5540df
    eu-west-1:
      AMI: ami-3bfab942
    ap-southeast-1:
      AMI: ami-e2adf99e
    ap-southeast-2:
      AMI: ami-43874721

## =================== CONDITIONS ===================
Conditions:
  isProd: !Equals [!Ref paramEnvironmentType, prod] # if 'prod' then TRUE, otherwise FALSE
  isDev: !Equals [!Ref paramEnvironmentType, dev]   # if 'dev' then TRUE, otherwise FALSE

## =================== RESOURCES ===================
Resources:
  myEC2Instance: # create a new EC2 instance
    Type: 'AWS::EC2::Instance'
    Properties:
      ImageId: !FindInMap # define imageId based on region
        - mapRegion # map's name
        - !Ref 'AWS::Region' # top level key which is a region where a new instance is being created
        - AMI # second level key - e.g. for 'us-east-1' the value for ImageId is 'ami-0ff8a91507f77f867'  
      InstanceType: !If [isProd, t2.micro, !If [isDev, t2.nano, t1.micro] ] # if 'prod', then t2.micro, (else) if 'dev' then t2.nano otherwise (if 'qa') then t1.micro  
      Tags:
      - Key: CloudFormationLab
        Value: !Join [' ', ['EC2 Instance for', !Ref AWS::Region] ] 

  myVolume: # create a new EBS volume only if environment is 'prod'
    Type: 'AWS::EC2::Volume'
    Condition: isProd # conditionally create EBS volume (only if environment is 'prod')
    Properties:
      Size: 100 # 100 GiB
      AvailabilityZone: !GetAtt myEC2Instance.AvailabilityZone # get AZ of a new EC2 instance
      Tags:
        - Key: CloudFormationLab
          Value: !Select [ 0, !Ref paramTagValues ] # output is 'JonSnow'
  
  myMountPoint: # attach an Amazon EBS volume to an EC2 instance only i environment is 'prod'
    Type: 'AWS::EC2::VolumeAttachment'
    Condition: isProd # conditionally attach EBS volume (only if environment is 'prod')
    Properties:
      InstanceId: !Ref myEC2Instance # ref to a new EC2 instance
      VolumeId: !Ref myVolume # ref to a new EBS volume
      Device: /dev/sdh