error on commas in AWS Tag values

[klauern]

There's a formatting specification for Tag Keys and Values. One issue with applying some changes is that you are disallowed from using certain characters (notably the ,) in a Tag Value, and this is not being caught by tflint currently.

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-resource-tags.html#w2ab1c25c10d254c13c17

[RyanDhuse]

I tripped on this one today with the "#" character. I'd be happy to put some effort into a merge request. Do the maintainers have some general direction on how this should be done?

[bendrucker]

Hey, working on making tags rules easier to write. The existing tags rule (missing_tags) is in pretty rough shape. terraform-linters/tflint#803 should lay the ground work. It adds a tags package within awsrules for dealing with tags that other tag-related rules can use.

https://github.com/terraform-linters/tflint/blob/master/rules/awsrules/aws_resource_missing_tags.go

I can see this being a aws_invalid_tags rule. In the mean time, might be helpful to start thinking about how to actually do this validation. If aws-sdk-go can do it (or even if not), you might also look into implementing this as field validator in terraform-provider-aws. TFLint should ideally suggest optional best practices and leave static validation to providers. The one exception is when a network connection would be required for validation, which Terraform validation forbids.

[wata727]

Yes, I think static validation should ideally be included in providers.
On the other hand, I think there are some challenges in static validations by providers:

• Since it is often performed in a later process such as CI, it is difficult to try easily.
• Validation error cannot be ignored, so it is difficult to incorporate specifications that change frequently.

I think providers should be able to solve this kind of problem in the future, but until then TFLint doesn't seem to be a bad idea to tackle this problem. So I'm positive about implementing this kind of rule.