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22 - Creating DNS Records ​

Working Code: terraform/exercise-22-creating-dns-records/

The Problem: Manually creating DNS records in a web UI is repetitive and error-prone (duplicates, CNAMEs pointing to themselves).

The Solution: Use Terraform to manage DNS as code with validation to catch errors.

Objective ​

Create:

  1. workhorse.g02... (A Record) → 1.2.3.4
  2. www.g02... (CNAME) → workhorse
  3. mail.g02... (CNAME) → workhorse
  4. Validation to prevent duplicates

How-to ​

1. Variables with Validation ​

hcl
variable "server_aliases" {
  default = ["www", "mail"]

  validation {
    condition     = length(distinct(var.server_aliases)) == length(var.server_aliases)
    error_message = "Duplicate server alias names found."
  }
}

2. Multiple Records with for_each ​

hcl
resource "dns_cname_record" "aliases" {
  for_each = toset(var.server_aliases)
  zone  = "sdi.hdm-stuttgart.cloud."
  name  = each.value
  cname = "workhorse.g02.sdi.hdm-stuttgart.cloud."
}

Troubleshooting ​

"Missing Resource State": DNS server accepted the request but didn't return confirmation. Fix by importing manually:

bash
terraform import 'dns_cname_record.aliases["www"]' 'g02.sdi.hdm-stuttgart.cloud./www'

Verify records resolved correctly:

bash
dig +noall +answer @ns1.hdm-stuttgart.cloud g2.sdi.hdm-stuttgart.cloud
dig +noall +answer @ns1.hdm-stuttgart.cloud workhorse.g2.sdi.hdm-stuttgart.cloud
dig +noall +answer @ns1.hdm-stuttgart.cloud www.g2.sdi.hdm-stuttgart.cloud
dig +noall +answer @ns1.hdm-stuttgart.cloud mail.g2.sdi.hdm-stuttgart.cloud