Better interaction between provider default_tags and aws_instance volume_tags

[acdha]

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Description

3.38.0 introduced the very handy provider-level default_tags which avoids a lot of tedious boilerplate. While migrating a large project, I noticed that EBS resources created by aws_instance do not use default_tags.

Obviously this could be resolved by changing volume_tags to inherit the default_tags values but I put this in as a feature request because it seems like a more generally useful situation would be making the provider's default_tags queryable in some way so it could be used for every resource type which has the concept of tags separate from the standard tags attribute — I'm pretty sure the same situation will arise with AWS Backup, for example — and it would be handy if you could reference the provider's configuration in something like merge(provider.aws.default_tags, var.extra_tags).

New or Affected Resource(s)

• aws_instance

Potential Terraform Configuration

aws_instance {
  volume_tags = merge(provider.aws.default_tags, var.extra_tags)
}

References

• Default tags for all resources #7926

[devopsrick]

I would argue that volume_tags should definitely inherit default_tags, if the idea behind default_tags is to replace the general use of tags on resources (except for overrides). Otherwise root ebs volumes of ec2 instances will not get tagged, while separate ebs volume will, and everything else.

[jtdoepke]

It should be documented that default_tags does not currently apply to aws_instance volume tags (and any resources with the same arguments like aws_spot_instance_request).

This note from the aws_instance documentation makes me think implementing default_tags here could be tricky:

NOTE:

Do not use volume_tags if you plan to manage block device tags outside the aws_instance configuration, such as using tags in an aws_ebs_volume resource attached via aws_volume_attachment. Doing so will result in resource cycling and inconsistent behavior.

[wedneyyuri]

Potential workaround where the provider is not available:

data "aws_default_tags" "example" {}
aws_instance {
  volume_tags = merge(aws_default_tags.example.default_tags, var.extra_tags)
}

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[github-actions]

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