[Enhancement]: Allow setting ignore_tags via environment variables

[bberg-indeed]

Description

We would like to be able to configure the ignore_tags parameter of the AWS provider using environment variables.

We have a process that applies a tag to AWS resources, and want to prevent this tag from being overwritten every time a Terraform plan is applied. Our organization has thousands of different instances of the AWS provider across several hundred repositories, making it difficult to ensure that every instance has ignore_tags configured correctly.

If ignore_tags were configurable via an environment variable, we could set it globally via a shared Terraform Enterprise variable set, eliminating the need to modify every instance of the AWS provider.

I propose the following environment variables:

• TF_AWS_IGNORE_TAGS_KEYS=<comma-separated list of keys>
• TF_AWS_IGNORE_TAGS_KEY_PREFIXES=<comma-separated list of key prefixes>

HCL string tuples would be another option for the format of the variables.

There is an additional question of how to resolve explicit specification of ignore_tags with specification via environment variables. I see a few options:

1. An explicit ignore_tags argument overrides both environment variables, regardless of whether keys, key_prefixes, or both are specified.
2. An explicit ignore_tags argument overrides TF_AWS_IGNORE_TAGS_KEYS iff it has a keys argument, and TF_AWS_IGNORE_TAGS_KEY_PREFIXES iff it has a key_prefixes argument.
3. Key and prefix sets specified via ignore_tags are merged with those specified via environment variables, rather than fully overriding them.

If we go with option 1 or 2, it would still be possible for module owners to explicitly merge the lists specified in TF_AWS_IGNORE_TAGS_KEYS or TF_AWS_IGNORE_TAGS_KEY_PREFIXES with an additional set of keys or prefixes via setunion(). With option 3, there would be no way for module owners to remove keys or prefixes from the ignore list, which may be regarded as a feature or limitation, depending on use case.

My preference is for option 3, merging, but I'm not sure which is more in line with Terraform's overall design philosophy. It would also be possible to specify override/merge behavior via an additional environment variable, although this would complicate things more than may be desirable.

Affected Resource(s) and/or Data Source(s)

• All resources managed by affected AWS providers

Potential Terraform Configuration

# Assume the following environment variables:
# TF_AWS_IGNORE_TAGS_KEYS=owner,commit
# TF_AWS_IGNORE_TAGS_KEY_PREFIXES=author_,team_

# Provider definition as written:
provider "aws" {
  region = "us-east-1"
  ignore_tags {
    keys = ["env"]
  }
}

# Effective provider definition, if option 3 is implemented (my preference):
provider "aws" {
  region = "us-east-1"
  ignore_tags {
    keys = ["owner", "commit", "env"]
    key_prefixes = ["author_", "team_"]
  }
}

# Effective provider definition if option 1 is implemented:
provider "aws" {
  region = "us-east-1"
  ignore_tags {
    keys = ["env"]
  }
}

# Effective provider definition if option 2 is implemented:
provider "aws" {
  region = "us-east-1"
  ignore_tags {
    keys = ["env"]
    key_prefixes = ["author_", "team_"]
  }
}

References

• Similar ticket with a pending PR to set default_tags via environment variable: [Enhancement]: default_tags from environment variables #33255
• Documentation for ignore_tags

Would you like to implement a fix?

Yes

[github-actions]

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[github-actions]

This functionality has been released in v5.62.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

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