feat: implement website alerting plan with Blackbox Exporter and VictoriaMetrics integration

hosts/web-arm/modules/grafana/alerting/websites/default.nix

@@ -0,0 +1,72 @@
+{ lib, pkgs, config, ... }:
+
+let
+  nginxVHosts = config.services.nginx.virtualHosts or {};
+  allDomains = lib.attrNames nginxVHosts;
+  httpsDomains = lib.map (d: "https://${d}") allDomains;
+  websiteAlertRules = lib.map (target:
+    let
+      domain = lib.replaceStrings ["://" "." "-" "/" ] ["-" "-" "_" "_"] target + "-down-alert";
+      uid = builtins.hashString "sha1" domain;
+    in {
+      uid           = uid;
+      title         = "Website " + target + " Down";
+      condition     = "C";
+
+      data = [
+        {
+          refId             = "A";
+          relativeTimeRange = { from = 300; to = 0; };
+          datasourceUid     = "vm-datasource-uid";
+          model = {
+            editorMode     = "code";
+            expr           = "probe_success{target=\"" + target + "\"} OR on() vector(0)";
+            hide           = false;
+            intervalMs     = 1000;
+            legendFormat   = target;
+            maxDataPoints  = 43200;
+            range          = true;
+            refId          = "A";
+          };
+        }
+        {
+          refId         = "B";
+          datasourceUid = "__expr__";
+          model = {
+            type       = "reduce";
+            expression = "A";
+            reducer    = "last";
+          };
+        }
+        {
+          refId         = "C";
+          datasourceUid = "__expr__";
+          model = {
+            type       = "math";
+            expression = "$B < 1";
+          };
+        }
+      ];
+      noDataState  = "Alerting";
+      execErrState = "Alerting";
+      for          = "5m";
+      annotations  = {
+        description = "Website " + target + " is unreachable.";
+        summary     = "Website Down";
+      };
+      labels = {
+        severity    = "critical";
+        website_url = target;
+      };
+    }
+  ) httpsDomains;
+in {
+  services.grafana.provision.alerting.rules.settings.groups = [
+    {
+      name     = "Website Alerts";
+      folder   = "Websites";
+      interval = "1m";
+      rules    = websiteAlertRules;
+    }
+  ];
+}

hosts/web-arm/modules/grafana/default.nix

@@ -31,6 +31,7 @@ in
     # Individual alert files removed, now handled by alerting/system/default.nix
     ./alerting/system/default.nix # Added: Imports the consolidated system alerts module
     ./alerting/service/default.nix # Added: Imports the new service alerts module
+    ./alerting/websites/default.nix # Added: Imports the new websites alerts module
     # ... other rule files can be added here ...
     ./datasources/victoriametrics.nix
     ./datasources/loki.nix # Add Loki datasource