fix: Use coalesce when desired default value is not null

[Roberdvs]

First of all, thanks for the work on this module. We've been using it for a couple of years now ❤️

Description

Use coalesce when the desired default value of an expression is not null.

Motivation and Context

We maintain an opinionated wrapper module around this one where we used to install the EKS add-ons using their separate Terraform resources but eventually switched to doing it through this module since it supports it.

On our module, we would like to support providing add-on versions while still keeping the default behavior from this module of retrieving the matching version from a data_source if no version is provided.

This would be a snippet from our module.

variable "coredns_version" {
  type    = string
  default = null
}

variable "kube_proxy_version" {
  type    = string
  default = null
}

...
  cluster_addons = {
    coredns = {
      addon_version = var.coredns_version
    }
    kube-proxy = {
      addon_version = var.kube_proxy_version
    }
...

But since null is a valid expression when using the try function; try(each.value.addon_version, data.aws_eks_addon_version.this[each.key].version) is returning null instead of defaulting to use the version from the data_source as we would like.

Using coalesce instead should fix this.

> try(null, "v1.26.2-eksbuild.1")
null
> coalesce(null, "v1.26.2-eksbuild.1")
"v1.26.2-eksbuild.1"

As a workaround, we could re-implement the same logic for retrieving add-on versions from data sources in our wrapper module or maybe use dynamic blocks, but if you don't see anything wrong with this change it would simplify our module a bit.

Breaking Changes

This might be be considered a breaking change since it would change the behavior for end users that are explicitly passing null as input variable to the module, but it probably won't affect many users.

How Has This Been Tested?

After an upgrade from EKS 1.25 to EKS 1.26 with this input:

  cluster_addons = {
    kube-proxy = {
      addon_version = var.kube_proxy_version <-- null
    }
}

plan with try:

No changes. Your infrastructure matches the configuration

plan with coalesce:

Terraform will perform the following actions:

  # module.cluster.module.eks.aws_eks_addon.this["kube-proxy"] will be updated in-place
  ~ resource "aws_eks_addon" "this" {
      ~ addon_version     = "v1.25.6-eksbuild.2" -> "v1.26.2-eksbuild.1"
        id                = "test:kube-proxy"
        tags              = {}
        # (7 unchanged attributes hidden)

      + timeouts {}
    }

I hope I've made myself clear 😛. Let me know your thoughts and if you are OK with this change. And if you wish I can extend it to all try occurrences where null is not the desired default value.

[bryantbiggs]

my apologies, I gave you one too many parenthesis:

Suggested change

	addon_version = coalesce(try(each.value.addon_version, null), data.aws_eks_addon_version.this[each.key].version))
	addon_version = coalesce(try(each.value.addon_version, null), data.aws_eks_addon_version.this[each.key].version)

[Roberdvs]

Changed! Thanks for the fix and sorry for the delay, I was disconnected these past days.

[bryantbiggs]

thank you!

[antonbabenko]

This PR is included in version 19.15.4 🎉

[github-actions]

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