Day-08: Meta Arguments in terraform

Source: Dev.to

Meta arguments

Terraform provides five meta‑arguments that control resource behavior:

• depends_on
• count
• for_each
• provider
• lifecycle

count

count is used for iterating over a list of values.

// variables.tf
variable "bucket_count_list" {
  type    = list(string)
  default = [
    "bhaskaratejabulusu-bucket-day-08-list-1",
    "bhaskaratejabulusu-bucket-day-08-list-2"
  ]
}

// main.tf
resource "aws_s3_bucket" "bucket1" {
  count  = length(var.bucket_count_list)
  bucket = var.bucket_count_list[count.index] // iterates from 0 to count‑1
}

for_each

for_each iterates over values or key‑value pairs. It works with maps and sets; the variable’s type must be either map or set.

Set example

// variables.tf
variable "bucket_count_set" {
  type    = set(string)
  default = [
    "bhaskaratejabulusu-bucket-day-08-set-1",
    "bhaskaratejabulusu-bucket-day-08-set-2"
  ]
}

// main.tf
resource "aws_s3_bucket" "bucket2" {
  for_each = var.bucket_count_set
  bucket   = each.value // iterates over the set
}

Map example

// variables.tf
variable "bucket_count_map" {
  type = map(string)
  default = {
    bucket1 = "bhaskaratejabulusu-bucket-day-08-map-1",
    bucket2 = "bhaskaratejabulusu-bucket-day-08-map-2"
  }
}

// main.tf
resource "aws_s3_bucket" "bucket3" {
  for_each = var.bucket_count_map
  bucket   = each.value
}

depends_on

depends_on explicitly declares a dependency between resources, ensuring Terraform creates them in the correct order.

// main.tf
resource "aws_s3_bucket" "bucket1" {
  count  = length(var.bucket_count_list)
  bucket = var.bucket_count_list[count.index]
}

resource "aws_s3_bucket" "bucket2" {
  for_each = var.bucket_count_set
  bucket   = each.value

  depends_on = [aws_s3_bucket.bucket1]
}

In this example, bucket2 depends on bucket1; Terraform will wait for bucket1 to be created before provisioning bucket2.