Remove code duplication in tags with for_each

Terraform
1

hello,
I have a list of tags that i’d like to apply to both EC2 and ebs volumes.
The EC2s defined as a map:

variable "vms" {
  type = map(object({
    ami     = string
    ...
    tag_productfamily = string
  }))
}

Non vm specific tags are in the “locals”:

locals {
  base_tags = {
    Client                = var.Client_abbr
     ....
  }
}

Currently I use the following code for ec2s ( and ) tags:

resource "aws_instance" "this" {
  for_each = var.vms
   ...
  ami           = data.aws_ami.AM2[each.key].id
  ....
tags = merge(
    {
      ...
      ProductFamily = "${each.value.tag_productfamily}"
      ...
    },
    local.base_tags
  )

  volume_tags = merge(
    local.base_tags,
    {
    ...
    ProductFamily = "${each.value.tag_productfamily}"
    ...
    }
  )

The desire is to eliminate the repeating lines for “ProductFamily”. But “for_each” is getting in a way.

Thank you for looking.

P.S. updated the original post by replacing “Name and Team” → “ProductFamily” to simplify the example.
P.P.S the use of “default_tags” is not ideal, since various products use different infrastructure in the same account.

2

There is no mention of “Name” or “Team” in your code, so there is nothing to eliminate.

3

@maxb ,
thank you for catching the mistake. I simplified the code, by replacing the “Name” and “Team” by “ProductFamily”, but did not update the description. Now all should be correct.

Thank you.

4

If it’s just the one tag, ProductFamily, then just live with the duplication. It’ll be shorter than what you might write instead.

If there are many tags, I guess you could compute the full set of tags within the for_each expression, but it probably won’t look very nice… something like

  for_each = { for name, info in var.vms: name => merge(info, {
    tags = merge({
      ProductFamily = info.tag_productfamily
    }, local.base_tags)
  })

  tags = each.value.tags
  volume_tags = each.value.tags

By the way, stop writing

just write

each.value.tag_productfamily

as wrapping simple expressions in "${ … }" has been deprecated since the language changes of Terraform 0.12.

1 Like
5

Agreed. The benefits for such complexity aren’t there.

Thank you @maxb!

6

i noticed that every time the code runs it either removes all tags or adds all of them.
Not sure why.

the simplified code is like this:

locals {
  base_tags = {
    Client                = var.Client_abbr
    ...
  }
}

...

resource "aws_instance" "this" {
  for_each = var.vms
  ...
  tags_all = merge(
    {
      ...
      ProductFamily = ${each.value.tag_productfamily}
      ...
    },
    local.base_tags
  )
}

the only difference i can see from the version discussed above is the use of “tags” vs current “tags_all”

The reason for using tags_all is to add provider level tags should I have them ( currently not defined).

7

looking for some help on for_each also.

I have a set of subnets that I specify via resource blocks, as everyone can imagine allot of code repetition.

sure it can be done with a for each loop based on az’s but my az’s would be az1, az2, az3 as the v of a k, v pair, where I for example need a, b, or c in my availability_zone tag.

sure someone’s done this… how could I change the 3 blocks into 1 using a for_each config.

G

resource "aws_subnet" "public_1" {
  # The VPC ID.
  vpc_id = aws_vpc.main.id

  # The CIDR block for the subnet.
  cidr_block = "192.168.11.0/24"

  # The AZ for the subnet.
  availability_zone = "af-south-1a"

  # Required for EKS. Instances launched into the subnet should be assigned a public IP address.
  map_public_ip_on_launch = true


 
# A map of tags to assign to the resource.
  tags = merge(
    local.tags,
    {
      Name                                        = "sn_pub-af-south-1a"
      "kubernetes.io/cluster/${var.cluster_name}" = "shared"
      "kubernetes.io/role/elb"                    = 1
    }
  )
}

resource "aws_subnet" "public_2" {
  # The VPC ID
  vpc_id = aws_vpc.main.id

  # The CIDR block for the subnet.
  cidr_block = "192.168.12.0/24"

  # The AZ for the subnet.
  availability_zone = "af-south-1b"

  # Required for EKS. Instances launched into the subnet should be assigned a public IP address.
  map_public_ip_on_launch = true

  # A map of tags to assign to the resource.
  tags = merge(
    local.tags,
    {
      Name                                        = "sn_pub-af-south-1b"
      "kubernetes.io/cluster/${var.cluster_name}" = "shared"
      "kubernetes.io/role/elb"                    = 1
    }
  )
}

resource "aws_subnet" "public_3" {
  # The VPC ID
  vpc_id = aws_vpc.main.id

  # The CIDR block for the subnet.
  cidr_block = "192.168.13.0/24"

  # The AZ for the subnet.
  availability_zone = "af-south-1c"

  # Required for EKS. Instances launched into the subnet should be assigned a public IP address.
  map_public_ip_on_launch = true

  # A map of tags to assign to the resource.
  tags = merge(
    local.tags,
    {
      Name                                        = "sn_pub-af-south-1c",
      "kubernetes.io/cluster/${var.cluster_name}" = "shared"
      "kubernetes.io/role/elb"                    = 1
    }
  )
}