refactor(role): Copy unit files instead of symlinking them

On each target machine we're storing the Git repo that has our unit
files underneath '/opt/git'. Prior to this commit we used to place
symlinks from '/etc/systemd/system' into the appropriate '/opt/git'
subdir. On most machines this worked fine, however, on some we
encountered a race condition on system start.

Sometimes '/opt/git' is not the same file system as '/'. If that's
the case chances are that systemd initializes the system and fails to
access a unit file at '/opt/git' because that file system is just
barely not yet visible early in the boot process.

For a timer unit for example this could result in enabling the unit
and upon reboot seeing that the unit no longer existed in systemd's
world view e.g. via 'systemctl list-timers' even though the symlink
at '/etc/systemd/system' still pointed to an '/opt/git' subdir when
inspected manually seconds after boot. journalctl, however, would
clearly confirm that at system initialization the symlink target was
inaccessible.

We could fiddle around with delaying boot until '/opt/git' and its
descendants are visible but the sane solution is to just not rely on
a separate file system for important stuff such as unit files. We now
copy unit files to '/etc/systemd/system' instead of symlinking them.

tasks/archlinux-auto-updates.yml

@@ -41,19 +41,18 @@
   notify:
     - 'Reload systemd unit configs'
 
-- name: 'If Arch Linux create symlinks to repo for OS auto-upgrades'
+- name: 'If Arch Linux copy systemd unit files for OS auto-upgrades to ''/etc/systemd/system'''
   when: 'ansible_facts[''os_family''] | lower == ''archlinux'''
   loop_control:
-    loop_var: 'genvm_os_auto_upgrades_symlink'
-    label: 'Create symlink to ''{{ genvm_os_auto_upgrades_symlink.target | basename }}'''
+    loop_var: 'genvm_os_auto_upgrades_unit'
+    label: 'Copy ''{{ genvm_os_auto_upgrades_unit.source | basename }}'' to ''/etc/systemd/system'''
   loop:
-    - { target: '{{ genvm_os_auto_upgrades_git_clone_dir }}/arch-linux-update-and-restart.service', symlink: '/etc/systemd/system/arch-linux-update-and-restart.service' }
-    - { target: '{{ genvm_os_auto_upgrades_git_clone_dir }}/arch-linux-update-and-restart.timer', symlink: '/etc/systemd/system/arch-linux-update-and-restart.timer' }
-  ansible.builtin.file:
-    src: '{{ genvm_os_auto_upgrades_symlink.target }}'
-    dest: '{{ genvm_os_auto_upgrades_symlink.symlink }}'
-    state: 'link'
-    force: true
+    - { source: '{{ genvm_os_auto_upgrades_git_clone_dir }}/arch-linux-update-and-restart.service', target: '/etc/systemd/system/arch-linux-update-and-restart.service' }
+    - { source: '{{ genvm_os_auto_upgrades_git_clone_dir }}/arch-linux-update-and-restart.timer', target: '/etc/systemd/system/arch-linux-update-and-restart.timer' }
+  ansible.builtin.copy:
+    src: '{{ genvm_os_auto_upgrades_unit.source }}'
+    dest: '{{ genvm_os_auto_upgrades_unit.target }}'
+    remote_src: true
   notify:
     - 'Reload systemd unit configs'