debian: fix interface file templating

Make it work for base Debian and Proxmox installs.

roles/debian/tasks/main.yml

@@ -1,3 +1,11 @@
+- block:
+    - name: Determine if this is a Proxmox host
+      stat:
+        path: /etc/pve
+      register: stat_pve
+    - set_fact:
+        is_proxmox: "{{ stat_pve.stat.exists and stat_pve.stat.isdir }}"
+
 - name: Configure MOTD
   template:
     dest: /etc/motd
@@ -33,21 +41,23 @@
       - rsync
       - vim
       - tmux
-    update_cache: yes
 
-# we don’t want to template this file because it gets overwritten by proxmox
-# so just try removing anything that messes with our definitions in interfaces.d
+# for base Debian the main interfaces file is just an include
 - name: Remove interface definitions added by installer
-  lineinfile:
-    path: /etc/network/interfaces
-    regexp: '^iface [^ ]* inet'
-    state: absent
+  when: not is_proxmox
+  copy:
+    dest: /etc/network/interfaces
+    content: 'source /etc/network/interfaces.d/*'
   notify: reload interfaces
 
+# for Proxmox the main interfaces file will define bridges
+# here we just remove the vmbr0 definition created by installer to preserve idempotency
 - name: Include interfaces.d definitions
+  when: is_proxmox
   lineinfile:
     path: /etc/network/interfaces
-    line: 'source /etc/network/interfaces.d/*'
+    regexp: '^(auto vmbr0|iface vmbr0|\t)' # our definitions start with four spaces instead of tab
+    state: absent
   notify: reload interfaces
 
 - name: Set up interfaces
@@ -77,7 +87,7 @@
 
 - name: Set up firewall
   include_tasks: firewall.yml
-  when: is_virtual or cluster_type != 'proxmox' # proxmox has its own firewall configuration
+  when: not is_proxmox # proxmox has its own firewall configuration
 
 - name: Install automatic upgrade package
   package:
@@ -114,5 +124,3 @@
         name: sshd@mgmt
         enabled: yes
       notify: reboot
-
-    - meta: flush_handlers