Reuse list of CloudFormation tags

Question

I have a rather complex set of CloudFormation templates that I use for provisioning the different environments of our infrastructure. However I recently got the request to tag the created resources with a rather extensive list of tags (like 15).

Hardcoding the tags into each of the template file doesn't seem like a good idea to me. I would rather create the list of tags once and refer to them for every taggeable resource. Problem is: I am not even sure this is possible. Do you know of any way that a reusable list of tags can be achieved?

I want to write this:

ECSAutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties: 
        ...
        Tags: !Ref ElTags

rather than

ECSAutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties: 
        ...
        Tags: !Ref ElTags
            - Key: Name
              Value: !Join ["-", [!Ref EnvironmentName, 'ecs-as-group'] ]
              PropagateAtLaunch: true
            - Key: TEAM
              Value: !Ref TeamName
              PropagateAtLaunch: true

Answer 1

You can easily reuse tags if you don't pass them to the template but instead reference them during deployment. The tags will be propagated to all ressources of the stack. A command similar to the one below might meet your needs:

aws cloudformation create-stack --stack-name mystack \
--template-body file://my_template.yaml --tags file://my_tags.json

The file my_tags.json is of the format

[
    {"Key": "mytag", "Value": "val"},
    ...
]

Alternatively, you could deploy your stack through CodePipeline and define the tags in the template configuration

Answer 2

This is possible using Fn::Transform function and AWS macro AWS::Include.

Fn::Transform specifies a macro to perform custom processing on part of a stack template

More about Fn::Transform on https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-transform.html

AWS::Include is an AWS CloudFormation macro which inserts a code snippet anywhere in your template.

More about AWS::Include on https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/create-reusable-transform-function-snippets-and-add-to-your-template-with-aws-include-transform.html

You can reuse your tags that way:

Resources:
  TestSG:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: 'SG for testing'
      GroupName: testSG
      SecurityGroupIngress:
        - CidrIp: '0.0.0.0/0'
          FromPort: 80
          IpProtocol: tcp
          ToPort: 80
      'Fn::Transform': 
        Name: AWS::Include 
        Parameters: 
          Location: 's3://bucket-name/tags.yaml'

  TestRole:
    Type: AWS::IAM::Role
    Properties: 
      AssumeRolePolicyDocument:
        Version: 2012-10-17
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns: 
        - 'arn:aws:iam::aws:policy/AmazonS3ReadOnlyAccess'
      RoleName: testRole
      'Fn::Transform': 
        Name: AWS::Include 
        Parameters: 
          Location: 's3://bucket-name/tags.yaml'

Your tags will be in a different template which will be placed on an S3 Bucket. This is the content of the file tags.yaml:

Tags: 
  - Key: tag1
    Value: value1
  - Key: tag2
    Value: value2
  - Key: tag3
    Value: value3
  - Key: tag4
    Value: value4
  - Key: tag5
    Value: value5
  - Key: tag6
    Value: value6
  - Key: tag7
    Value: value7
  - Key: tag8
    Value: value8
  - Key: tag19
    Value: value9
  - Key: tag10
    Value: value10