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17 - Host Metadata Generation ​

Working Code: terraform/exercise-17-host-metadata/

The Problem: Other tools (Ansible, monitoring) need server IPs/names, but Terraform locks that in its state file.

The Solution: Terraform generates a JSON file for each server with its metadata.

Objective ​

Create a module that builds a server and writes Gen/<hostname>.json with its details.

How-to ​

1. The Module ​

hcl
# modules/host_metadata/main.tf
resource "local_file" "meta" {
  filename = "Gen/${var.name}.json"
  content  = jsonencode({
    ipv4     = var.ipv4
    ipv6     = var.ipv6
    location = var.location
  })
}

2. Call the Module ​

hcl
module "web_metadata" {
  source = "./modules/host_metadata"

  name     = hcloud_server.web.name
  ipv4     = hcloud_server.web.ipv4_address
  location = hcloud_server.web.location
}

3. Result ​

After terraform apply, Gen/ folder contains JSON files for other tools to parse.

Problems & Learnings ​

Common Issues

  • Terraform server creation takes 5+ minutes — caused by package_reboot_if_required: true triggering a server reboot mid-provisioning. The Hetzner provider polls through the reboot. Set to false.
  • Gen/web-server-01.json not found — the metadata file is named after the actual server (e.g. Gen/metadata-server-1.json). Use terraform output -raw server_name to get the correct name.

Key Takeaways

  • The metadata filename is dynamic — always use terraform output -raw server_name to reference it
  • Auto-incrementing server names query existing Hetzner servers at plan time, so the name is only known after apply