AWS CloudFormation条件标记

Question

I have a requirement to conditionally tag resources based on user response to the downtime parameter and the value of environment defined in map. This tag is later used by the lambda function to turn off the instances at night.

I tried it like this with no luck -

Conditions -

    "EnvCheck": {
        "Fn::Not": [
            {"Fn::Equals": [{"Ref": "EnvironmentType"}, "prod"]}
        ]
    },
    "EnableDowntimeTag": {
        "Fn::And": [
            {"Fn::Equals": [{"Ref": "CustodianDowntime"}, "true"]},
            {"Condition": "EnvCheck"}
        ]
    }

Tags section

    "Tags": [
                {
                    "Key": "OwnerContact",
                    "PropagateAtLaunch": "true",
                    "Value": {
                        "Ref": "OwnerContact"
                    }
                },
                {
                    "Condition" : "EnableDowntimeTag",
                    "Key": "custodian_downtime",
                    "PropagateAtLaunch": "true",
                    "Value": "Offhours tz=ET"
                }
            ],

Any idea on how to add a conditional tag?

Thanks!

Answer 1

I have a similar need and don't want unused tags lying around either. I've gotten it working using the following snippet:

"Tags": [
  ...,
  {
    "Fn::If": [
      "MyCondition",
      {"Key": "MyKey", "Value": "MyValue"},
      {"Ref": "AWS::NoValue"}
    ]
  }
],

Answer 2

Unfortunately I don't think it's possible to conditionally add a tag. The best you can do is use the condition to modify the data for the tag - either the key or value or both. If you modify the key, then any automated searching for the expected tag key will not find resources with the modified key. But you will get left with unnecessary tags lying around.

eg

"Tags": [
    {
        "Key": "OwnerContact",
        "PropagateAtLaunch": "true",
        "Value": {
            "Ref": "OwnerContact"
        }
    },
    {
        "Key": { 
            "Fn::If" : [
                "EnableDowntimeTag",
                "custodian_downtime",
                "no_custodian_downtime"
            ]
        },
        "PropagateAtLaunch": "true",
        "Value": { 
            "Fn::If" : [
                "EnableDowntimeTag",
                "Offhours tz=ET",
                ""
            ]
        }
    }
],

With this, if the condition EnableDowntimeTag is true, then a tag with key custodian_downtime is created, and a value of Offhours tz=ET .

If the condition is not true, a tag with key no_custodian_downtime is created, with an empty value.

If you are using the tags to identify resources from an automated process, this should help it to only identify the required resources - while also providing an explicit reference on those with the no_custodian_downtime tag that there is no downtime required - so it could be even more helpful.

Answer 3

And if you're using YAML

  Tags:
    - 'Fn::If':
      - MyCondition
      -
        Key: MyKey
        Value: MyValue
      - !Ref AWS::NoValue