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Using Dynamic Blocks in Terraform

9/20/2023: The open source version of Terraform is now OpenTofu 

 

Want to read it with nice formatting? Check out the Notion page. Continuing from the post about Modules, let's look at Dynamic Blocks.

What are Dynamic Blocks?

It's a way to construct dynamically repeatable nested blocks in Terraform code. Think about using for_each - This is often used to make individual resources with a value to iterate over.

Is This a Dynamic Block?

I’ve done something like this, but it involved the multiple function (*) and a stand-in variable ${var.ex} .

network_interface_ids = ["${element(azurerm_network_interface.CA-NetInt.*.id, 01)}"]

The index (01) was the number of network_interface_ids one would want.

Was that unknowingly a dynamic block, or something else? By all means, comment what you think.

Apparently, It Wasn’t

resource "aws_elastic_beanstalk_environment" "tfenvtest" {
  name                = "tf-test-name"
  application         = "${aws_elastic_beanstalk_application.tftest.name}"
  solution_stack_name = "64bit Amazon Linux 2018.03 v2.11.4 running Go 1.12.6"

  dynamic "setting" {
    for_each = var.settings
    content {
      namespace = setting.value["namespace"]
      name = setting.value["name"]
      value = setting.value["value"]
    }
  }
}
  • There are different kinds of dynamic blocks - setting up there is one. Others are list and map,and will reference different values.
  • for_each - The ieterative variable
  • Not to be confused with the ieterator argument, which is option, and sets the name of a temp var. Since it’s not here, it’s defaulting to setting up there.
  • setting has two attributes;
    • keymaps the key or lists element index for the current element. It will be identical to valueif the expression has the set value.
    • value is the value of the current element.
  • Nested content defines the body of each generated block. It doesn’t seem to match the variables in the resource block.

We can’t generate meta-argument blocks like lifecycle or provisioner.

References:

Using Dynamic Blocks in Terraform - Ned In The Cloud

Terraform docs

 

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