Writing Terraform configurations

Use locals to specify explicit dependencies between resources

Helpful way to give a hint to Terraform that some resources should be deleted before even when there is no direct dependency in Terraform configurations.

https://raw.githubusercontent.com/antonbabenko/terraform-best-practices/master/snippets/locals.tf

Terraform 0.12 - Required vs Optional arguments

1. Required argument index_document must be set, if var.website is not an empty map.

2. Optional argument error_document can be omitted.

main.tf

variable "website" {
  type    = map(string)
  default = {}
}

resource "aws_s3_bucket" "this" {
  # omitted...

  dynamic "website" {
    for_each = length(keys(var.website)) == 0 ? [] : [var.website]

    content {
      index_document = website.value.index_document
      error_document = lookup(website.value, "error_document", null)
    }
  }
}

terraform.tfvars

website = {
  index_document = "index.html"
}