Create Prometheus metrics

This patch allows the automation to provide Prometheus metrics exposing
the last time a backup succeeded.

Author: lkiesow

README.md

@@ -10,10 +10,23 @@ There are three required variables you need to set:
 * `backup_smb_user`: the user that will access the backup cloud
 * `backup_smb_password`: the password for this user
 * `backup_script`: The shell commands to run for creating a backup
+* `backup_metrics_path`: Write Prometheus metrics about updates to this file
 
 Have a look at the [defaults](defaults/main.yml) to see all variables and how to set them.
 
 
+## Prometheus Metrics
+
+The backup automation can create metrics for Prometheus.
+The metrics are written to file which can then be exposed via a web server like Apache or Nginx.
+The metrics provide the time of the last successful backup.
+
+```openmetrics
+# HELP backup_time Time stamp of backup
+# TYPE backup_time counter
+backup_time 1735876976
+```
+
 ## Example Playbook
 
 Your playbook, could look like this:
@@ -29,6 +42,7 @@ Your playbook, could look like this:
         backup_script: |
           FILENAME="{{ backup_mountpoint }}/$(date '+%Y%m%d-%H%M%S').sql.gz"
           mysqldump -u root dbname | gzip > "${FILENAME}"
+        backup_metrics_path: /var/lib/nginx/backup/metrics
 ```
 
 ## License

defaults/main.yml

@@ -29,3 +29,6 @@ backup_cleanup: >-
   -mindepth 2
   -mtime "+{{ backup_keep_days }}"
   -exec rm -rfv '{}' \;
+
+## Path for backup metrics
+backup_metrics_path: ""

tasks/main.yml

@@ -59,6 +59,17 @@
     - backup.timer
   notify: Restart backup
 
+- name: Set permissions of backup file
+  ansible.builtin.file:
+    path: '{{ backup_metrics_path }}'
+    state: touch
+    mode: '0644'
+    owner: '{{ backup_user }}'
+    group: '{{ backup_group }}'
+    modification_time: preserve
+    access_time: preserve
+  when: backup_metrics_path != ""
+
 - name: Start backup timer
   ansible.builtin.service:
     name: backup.timer

templates/backup

@@ -3,3 +3,9 @@
 set -eux
 
 {{ backup_script }}
+
+{% if backup_metrics_path %}
+echo '# HELP backup_time Time stamp of backup' > "{{ backup_metrics_path }}"
+echo '# TYPE backup_time counter' >> "{{ backup_metrics_path }}"
+echo "backup_time $(date +%s)" >> "{{ backup_metrics_path }}"
+{% endif %}