Limit Borg CPU usage on single vCPU servers to 50%

This is meant to address the daily HostHighCpuLoad alert triggered on
lists.archlinux.org, which due to the large number of files it has to
process (around 1.5 million). Machines with more than one virtual CPU
don't need this as Borg is currently single-threaded and thus limited
to one core.

roles/borg_client/tasks/main.yml

@@ -57,12 +57,14 @@
   template: src=backup-gitlab.sh.j2 dest=/usr/local/bin/backup-gitlab.sh owner=root group=root mode=0755
   when: inventory_hostname == "gitlab.archlinux.org"
 
-- name: install systemd timer and service for backup
-  copy: src={{ item }} dest=/etc/systemd/system/{{ item }} owner=root group=root mode=0644
+- name: install systemd services for backup
+  template: src={{ item }}.j2 dest=/etc/systemd/system/{{ item }} owner=root group=root mode=0644
   with_items:
-    - borg-backup.timer
     - borg-backup.service
     - borg-backup-offsite.service
 
-- name: activate systemd timers for backup
+- name: install systemd timer for backup
+  copy: src=borg-backup.timer dest=/etc/systemd/system/borg-backup.timer owner=root group=root mode=0644
+
+- name: activate systemd timer for backup
   systemd: name=borg-backup.timer enabled=yes state=started daemon-reload=yes

roles/borg_client/templates/borg-backup-cpu-quota.j2

+{% if ansible_processor_vcpus == 1 %}
+{# Limit CPU usage to avoid triggering a HostHighCpuLoad alert #}
+CPUQuota=50%
+{% endif %}

roles/borg_client/files/borg-backup-offsite.service → roles/borg_client/templates/borg-backup-offsite.service.j2

@@ -5,4 +5,5 @@ Description=Borg backup (offsite)
 Type=oneshot
 Restart=on-failure
 RestartSec=5m
+{% include 'borg-backup-cpu-quota.j2' %}
 ExecStart=/usr/local/bin/borg-backup-offsite.sh

roles/borg_client/files/borg-backup.service → roles/borg_client/templates/borg-backup.service.j2

@@ -7,4 +7,5 @@ Before=borg-backup-offsite.service
 Type=oneshot
 Restart=on-failure
 RestartSec=5m
+{% include 'borg-backup-cpu-quota.j2' %}
 ExecStart=/usr/local/bin/borg-backup.sh