Introduction
Part of the 2023 Cornell AWS Direct Connect Architecture Migration process creates new tags on Cornell AWS VPCs that use Direct Connect. Those tags, prefixed by "cit:", can cause Terraform to hiccup if you use Terraform to manage AWS network resources.
Please don't allow Terraform to delete the tags prefixed by "cit:", or the "Cost Center" tag! They are important for the migration to the v2 Direct Connect architecture. If you (or Terraform) delete those tags, they will be recreated before the migration proceeds. Deleting the "Cost Center" tag on TGW attachments will result in customers paying for TGW attachment costs instead of CIT.
This is what it looks like when Terraform finds those tags, and makes a plan to delete them:
# terraform plan
aws_vpc.blank-vpc: Refreshing state... [id=vpc-cde7e0a8]
...
aws_route_table_association.v2-private-1: Refreshing state... [id=rtbassoc-08f9e7ea923cc8454]
Terraform used the selected providers to generate the following execution plan. Resource actions are
indicated with the following symbols:
~ update in-place
Terraform will perform the following actions:
# aws_subnet.example will be updated in-place
~ resource "aws_subnet" "example" {
id = "subnet-0d705338215b4d08b"
~ tags = {
- "cit:dc-arch-migration-description" = "No change." -> null
- "cit:dc-arch-migration-target" = "no" -> null
- "cit:dc-arch-version" = "v1" -> null
- "cit:subnet-type" = "public" -> null
# (1 unchanged element hidden)
}
~ tags_all = {
- "cit:dc-arch-migration-description" = "No change." -> null
- "cit:dc-arch-migration-target" = "no" -> null
- "cit:dc-arch-version" = "v1" -> null
- "cit:subnet-type" = "public" -> null
# (1 unchanged element hidden)
}
# (14 unchanged attributes hidden)
}
Plan: 0 to add, 1 to change, 0 to destroy.
Tell Terraform to Ignore the Tags
You can tell Terraform to ignore those tags by adding a lifecycle stanza to the resource and setting the ignore_changes attribute as shown below. The next time you run Terraform plan/apply, Terraform will ignore any of those tags.
Terraform Versions >= 0.12.3
Recent Terraform Versions (>= v0.13)
resource "aws_subnet" "example" {
cidr_block = "10.92.117.128/25"
vpc_id = aws_vpc.example.id
...
tags = {
Name = "example-subnet"
}
lifecycle {
ignore_changes = [
tags["cit:dc-arch-migration-description"],
tags["cit:dc-arch-migration-target"],
tags["cit:dc-arch-version"],
tags["cit:dc-vgw"],
tags["cit:subnet-type"],
tags["cit:tgw-attachment-target"],
tags["cit:tgw-attachment-guidance"],
tags["Cost Center"],
]
}
}
Terraform Version 0.12.0 through 0.12.2
You will need to upgrade Terraform to at least version 0.12.3 and then use the configuration above.
Terraform Versions 0.11.x
Terraform v0.11.x
resource "aws_subnet" "example" {
cidr_block = "10.92.117.128/25"
vpc_id = aws_vpc.example.id
...
tags = {
Name = "example-subnet"
}
lifecycle {
ignore_changes = [
"tags.%",
"tags.cit:dc-arch-migration-description",
"tags.cit:dc-arch-migration-target",
"tags.cit:dc-arch-version",
"tags.cit:dc-vgw",
"tags.cit:subnet-type",
"tags.cit:tgw-attachment-target",
"tags.cit:tgw-attachment-guidance",
"tags.Cost Center",
]
}
}
Last Ditch Options
If your Terraform version or AWS provider version doesn't support (or behave as expected) with the options above, you should be able to, at least, tell Terraform to ignore all changes to tags, as shown below:
lifecycle {
ignore_changes = [ tags ]
}
Or...
lifecycle {
ignore_changes = [ "tags" ]
}