Node VPN alert for Subscription

[DavidePrincipi]

Raise a my.nethserver.com / my.nethesis.it alert if a worker node Wireguard VPN link is down.

[gsanchietti]

The new monitor system uses node_exporter metrics to generate the alerts.
Before proceeding with QA of this issue, please make sure to have installed the latest version from #7162

An alert is raised when Prometheus can't reach a target node.

Test case

• Register the cluster with a valid subscription token
• Disable node_exporter on the worker node: systemctl stop node_exporter
• Verify no alert is sent, inside the logs you should see something like:

  Feb 25 08:48:53 rl1.leader.cluster0.gs.nethserver.net alert-proxy[137405]: ALERT CRITICAL node:offline:1
  

• Verify the alert is received by my.nethesis.it
• Restart node_exporter on the worker_node: systemctl start node_exporter
• Verify the alert is resolved inside my.nethesis.it

[DavidePrincipi]

In testing core 3.5.0-dev.5

[DavidePrincipi]

VERIFIED

Node is offline:

[root@rl4 ~]# curl  -s  http://127.0.0.1:9091/api/v1/alerts | jq
{
  "status": "success",
  "data": {
    "alerts": [
      {
        "labels": {
          "alertname": "node_offline",
          "instance": "10.5.4.2:9100",
          "job": "providers",
          "node": "2",
          "severity": "critical"
        },
        "annotations": {
          "description": "A cluster target has disappeared. An exporter might be crashed.\n  VALUE = 0\n  LABELS = map[__name__:up instance:10.5.4.2:9100 job:providers node:2]",
          "summary": "Cluster node offline (instance 10.5.4.2:9100)"
        },
        "state": "firing",
        "activeAt": "2025-03-05T10:41:08.181011444Z",
        "value": "0e+00"
      }
    ]
  }
}

Mail received from my.nethserver.com when alarm is fired and on resolution.