dynamic blocks

expected time	requirements
45 minutes	A computer with Terraform installed, terraform knowledge.

Goal: See how you may use Terraform dynamic blocks.

Explanation

Sometimes you want to loop over a list and repeat a “block”. For example tcp-ports that should be allowed to access a resource.

This can be a challenge because the looping need to happen in a resource. Think if this example:

resource "x" "y" {
  name = "my-thing"
  allow {
    port = 80
  }
  allow {
    port = 443
  }
}

It’s anoying to repeat this allow block. Dynamic blocks to the rescue!

Howto

With the resource and variables as described above, you can use a dynamic block:

variable "allow" {
  default = [
    {
      port = 80
    },
    {
      port = 443
    }
  ]
}

resource "x" "y" {
  name = "my-thing"
  dynamic "allow" {
    for_each = var.allow
    content {
      port = allow.value.port
    }
  }
}

Dynamic blocks are required from time to time, but a person less terraform-skilled may find this construct difficult to understand.

You can use blocks-in-blocks, making the code even harder to read.

Demo

Have a look here.

Assignment

1. Find a resource with a repeating block in it. Here are some suggestions:

• bigquery_dataset.
• pubsub_topic.
• compute_instance_group.
• Or any other that you know or can find.

1. Write the resource, but replace the repeating block with a dynamic block.
2. Add a variable to pass the values used in the dynamic_block.

Questions

1. Is there currently any (root) module in use that can benefit from a dynamic block?