Make local_admin, base_volume and ssh_private_key optional

When trying to use this module with my own configuration, I found myself
with some needs that think can be usefull to make this module more
reusable:

* Storage management: added two variables to use existing base images an
  not always uploading a base image
  * base_pool_name: define an existing pool name
  * base_volume_name: define an existing base volume name
* Local user management: when this variable is empty do not create a
  local_user. Changed default value to make this a default behaviour.
* Test vm connection: in almost all cases users would use their default
  private key, that may be loaded with ssh-agent. So default behaviour
  seems to be null value, but allow to define a different value

Author: chrodriguez

main.tf

@@ -66,12 +66,11 @@ resource "libvirt_domain" "virt-machine" {
       "echo \"Virtual Machine \"$(hostname)\" is UP!\"",
       "date"
     ]
-
     connection {
       type                = "ssh"
       user                = var.ssh_admin
       host                = self.network_interface.0.addresses.0
-      private_key         = file(var.ssh_private_key)
+      private_key         = var.ssh_private_key != null ? file(var.ssh_private_key): null
       timeout             = "2m"
     }
   }

storage.tf

@@ -1,4 +1,5 @@
 resource "libvirt_volume" "base-volume-qcow2" {
+  count = var.base_volume_name != null ? 0 : 1
   name   = format("${var.vm_hostname_prefix}-base.qcow2")
   pool   = var.pool
   source = var.os_img_url
@@ -10,7 +11,10 @@ resource "libvirt_volume" "volume-qcow2" {
   name   = format("${var.vm_hostname_prefix}%02d.qcow2", count.index + var.index_start)
   pool   = var.pool
   size   = 1024*1024*1024*var.system_volume
-  base_volume_id = libvirt_volume.base-volume-qcow2.id
+  base_volume_id = var.base_volume_name != null ? null : element(libvirt_volume.base-volume-qcow2, 0).id
+  base_volume_name = var.base_volume_name
+  base_volume_pool = var.base_pool_name
+
   format = "qcow2"
 }
 
@@ -20,4 +24,4 @@ resource "libvirt_cloudinit_disk" "commoninit" {
   user_data      = data.template_cloudinit_config.init_config[count.index].rendered
   network_config = data.template_file.network_config[count.index].rendered
   pool           = var.pool
-}
+}

templates/cloud_init.tpl

@@ -22,12 +22,14 @@ users:
     system: False
     ssh_authorized_keys: ${ssh_keys}
     shell: /bin/bash
+%{ if local_admin != "" }
   - name: ${local_admin}
     gecos: Local admin (no SSH)
     lock-passwd: false
     sudo: ALL=(ALL) ALL
     passwd: ${local_admin_passwd}
     shell: /bin/bash
+%{ endif }
 
 write_files:
   - path: /etc/ssh/sshd_config

variables.tf

@@ -3,6 +3,17 @@ variable "os_img_url" {
   default     = "https://cloud-images.ubuntu.com/focal/current/focal-server-cloudimg-amd64.img"
 }
 
+variable "base_volume_name" {
+  description = "Name of base OS image"
+  default     = null
+}
+
+variable "base_pool_name" {
+  description = "Name of base OS image"
+  default     = null
+}
+
+
 variable "autostart" {
   description = "Autostart the domain"
   default = true
@@ -111,7 +122,7 @@ variable "ssh_keys" {
 
 variable "local_admin" {
   description = "Admin user without ssh access"
-  default     = "local-admin"
+  default     = ""
 }
 
 variable "local_admin_passwd" {
@@ -126,5 +137,5 @@ variable "time_zone" {
 
 variable "ssh_private_key" {
   description = "Private key for SSH connection test"
-  default     = "~/.ssh/id_ed25519"
+  default     = null
 }