terraform-setsubtract

#terraform-setsubtract

I recently used setsubtract to solve a buggy terraform pipeline. In short I needed to remove the listitem “latest”. The problem was the new list afterwards I could not reference item 0 in the list. I am not sure why because using terraform output to check the two lists they look good. Adding a typecast tolist() worked though.

code

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❯❯ cat variables.tf
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locals {
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  images = ["1", "latest", "2"]
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  remove_list = ["latest"]
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  # need tolist here: https://github.com/hashicorp/terraform/issues/23882
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  image_list = tolist(setsubtract(local.images , ["latest"]))
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}
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output orig_list {
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  value = local.images
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}
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output new_list {
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  value = local.image_list
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}
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output images_0 {
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  value = local.image_list[0]
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}

check it

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❯❯ terraform plan
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Changes to Outputs:
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  + images_0  = "1"
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  + new_list  = [
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      + "1",
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      + "2",
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    ]
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  + orig_list = [
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      + "1",
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      + "latest",
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      + "2",
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    ]