prometheus: fix HostOutOfDiskSpace alert expression

It previously used mountpoint="/rootfs" which didn't match any mounts.

Also fix HostOutOfInodes and tweak HostDiskWillFillIn24Hours slightly.

roles/prometheus/files/node.rules.yml

@@ -57,16 +57,16 @@ groups:
           description: "Host network interfaces are probably sending too much data (> 100 MB/s)\n  VALUE = {{ $value }}\n  LABELS: {{ $labels }}"
 
       - alert: HostOutOfDiskSpace
-        expr: (node_filesystem_avail_bytes{mountpoint="/rootfs"}  * 100) / node_filesystem_size_bytes{mountpoint="/rootfs"} < 10
+        expr: (node_filesystem_avail_bytes{fstype!="tmpfs",mountpoint!~"/backup.*"} * 100) / node_filesystem_size_bytes < 10
         for: 5m
         labels:
           severity: warning
         annotations:
           summary: "Host out of disk space (instance {{ $labels.instance }})"
-          description: "Disk is almost full (< 20% left)\n  VALUE = {{ $value }}\n  LABELS: {{ $labels }}"
+          description: "Disk is almost full (< 10% left)\n  VALUE = {{ $value }}\n  LABELS: {{ $labels }}"
 
       - alert: HostDiskWillFillIn24Hours
-        expr: (node_filesystem_avail_bytes{mountpoint!~"/backup"} * 100) / node_filesystem_size_bytes < 10 and ON (instance, device, mountpoint) predict_linear(node_filesystem_avail_bytes{fstype!~"tmpfs",mountpoint!~"/backup"}[1h], 24 * 3600) < 0 and ON (instance, device, mountpoint) node_filesystem_readonly == 0
+        expr: (node_filesystem_avail_bytes{fstype!="tmpfs",mountpoint!~"/backup.*"} * 100) / node_filesystem_size_bytes < 10 and predict_linear(node_filesystem_avail_bytes[1h], 24 * 3600) < 0
         for: 2m
         labels:
           severity: warning
@@ -75,7 +75,7 @@ groups:
           description: "Filesystem is predicted to run out of space within the next 24 hours at current write rate\n  VALUE = {{ $value }}\n  LABELS: {{ $labels }}"
 
       - alert: HostOutOfInodes
-        expr: node_filesystem_files_free{mountpoint ="/rootfs"} / node_filesystem_files{mountpoint ="/rootfs"} * 100 < 10
+        expr: (node_filesystem_files_free{fstype!="tmpfs",mountpoint!~"/backup.*"} * 100) / node_filesystem_files < 10
         for: 5m
         labels:
           severity: warning