add node-exporter disk space alert

Author: sjpb

environments/common/files/prometheus/rules/node-exporter.rules

@@ -0,0 +1,14 @@
+groups:
+- name: node-exporter
+  rules:
+  # Please add ignored mountpoints in node_exporter parameters like
+  # "--collector.filesystem.ignored-mount-points=^/(sys|proc|dev|run)($|/)".
+  # Same rule using "node_filesystem_free_bytes" will fire when disk fills for non-root users.
+  - alert: HostOutOfDiskSpace
+    expr: (node_filesystem_avail_bytes{fstype!~"^(fuse.*|tmpfs|cifs|nfs)"} / node_filesystem_size_bytes < .10 and on (instance, device, mountpoint) node_filesystem_readonly == 0)
+    for: 2m
+    labels:
+      severity: critical
+    annotations:
+      summary: Host out of disk space (instance {{ $labels.instance }})
+      description: 'Disk is almost full (< 10% left)\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}'