fix: restore host disk alerts validation in main.yml and remove redundant check from alerting.yml

Author: tazlin

roles/horde_monitoring/tasks/alerting.yml

@@ -4,19 +4,9 @@
 #
 # The rendered rules file is placed in the Prometheus rules directory where
 # it is automatically loaded by Prometheus via the rule_files glob.
-
-- name: Fail when host disk alerts are enabled without host filesystem metrics
-  ansible.builtin.fail:
-    msg: >-
-      horde_monitoring_install_host_disk_alerts=true requires
-      node_filesystem_* metrics in Prometheus.
-      Set horde_monitoring_host_filesystem_metrics_available=true only when
-      host filesystem metrics are actually ingested (node_exporter or Alloy),
-      or disable host disk alerts with horde_monitoring_install_host_disk_alerts=false.
-  when:
-    - horde_monitoring_start_services | bool
-    - horde_monitoring_install_host_disk_alerts | default(true) | bool
-    - not (horde_monitoring_host_filesystem_metrics_available | default(false) | bool)
+# NOTE: the host-filesystem metrics prerequisite guard lives in tasks/main.yml
+# (before any include_tasks) so it fires as a true pre-flight check regardless
+# of which backends are being installed.
 
 - name: Probe Prometheus targets for postgres job (when postgres alerts enabled)
   ansible.builtin.uri:

roles/horde_monitoring/tasks/main.yml

@@ -5,6 +5,19 @@
 # using the prometheus.prometheus.prometheus community role.
 
 # ── Flag-combination validation ────────────────────────────
+- name: Fail when host disk alerts are enabled without host filesystem metrics
+  ansible.builtin.fail:
+    msg: >-
+      horde_monitoring_install_host_disk_alerts=true requires
+      node_filesystem_* metrics in Prometheus.
+      Set horde_monitoring_host_filesystem_metrics_available=true only when
+      host filesystem metrics are actually ingested (node_exporter or Alloy),
+      or disable host disk alerts with horde_monitoring_install_host_disk_alerts=false.
+  when:
+    - horde_monitoring_start_services | bool
+    - horde_monitoring_install_host_disk_alerts | default(true) | bool
+    - not (horde_monitoring_host_filesystem_metrics_available | default(false) | bool)
+
 - name: Warn when backup is enabled but S3 storage is disabled
   ansible.builtin.debug:
     msg: >-