Terrfaform execution plan

Terraform Providers Plugin Development
1

I’m creating a simple tag resource in my custom provider that will look something like:

resource "provider_tag" "my-foo-tag" {
  name = "foo"
}

It will have name attribute and another id that will have the same value as name. When changing the name I get:

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:

  # provider_tag.my-foo-tag will be updated in-place
  ~ resource "provider_tag" "my-foo-tag" {
      ~ id   = "foo" -> (known after apply)
      ~ name = "foo" -> "bar"
    }

Plan: 0 to add, 1 to change, 0 to destroy.

I’m curios how does Terraform execution plan knows when to perform an update in-place or a complete destroy and recreation? It seems to me that since the id changes it should not be an update in place, but maybe I’m missing something.

Thanks for any input!

2

Hi @zuzuleinen,

There is nothing special about id from Terraform’s perspective, it’s just an attribute like any other. It’s up to the provider to indicate when a change is going to cause replacement. For example, if you are using the plugin framework you could add a stringplanmodifier.RequiresReplace() to indicate that a change to an attribute will force replacement of the resource instance.

1 Like
3

Thanks @jbardin,

stringplanmodifier.RequiresReplace() is useful. So it is safe to assume that when an attribute is changed, the update will alayws be in-place, and if this behavior has to be changed a RequiresReplace modified should be added?

later edit: Actually I see this is the case as I wrote above:

In-place update is part of the basic Terraform lifecycle for managing resources. To ensure that Terraform plans replacement of a resource, rather than perform an in-place update, use the [resource.RequiresReplace() attribute plan modifier](https://pkg.go.dev/github.com/hashicorp/terraform-plugin-framework/resource#RequiresReplace) in the schema or implement [resource plan modification](https://developer.hashicorp.com/terraform/plugin/framework/resources/plan-modification). source

Thank you!