Add NodeSystemdServiceCrashlooping alert to mixin (#3039)

* Add NodeSystemdServiceCrashlooping alert

---------

Signed-off-by: Vitaly Zhuravlev <[email protected]>

Author: v-zhuravlev

docs/node-mixin/alerts/alerts.libsonnet

@@ -407,6 +407,20 @@
               description: 'Systemd service {{ $labels.name }} has entered failed state at {{ $labels.instance }}',
             },
           },
+          {
+            alert: 'NodeSystemdServiceCrashlooping',
+            expr: |||
+              increase(node_systemd_service_restart_total{%(nodeExporterSelector)s}[5m]) > 2
+            ||| % $._config,
+            'for': '15m',
+            labels: {
+              severity: 'warning',
+            },
+            annotations: {
+              summary: 'Systemd service keeps restaring, possibly crash looping.',
+              description: 'Systemd service {{ $labels.name }} has being restarted too many times at {{ $labels.instance }} for the last 15 minutes. Please check if service is crash looping.',
+            },
+          },
           {
             alert: 'NodeBondingDegraded',
             expr: |||