feat: implement centralized alerting with vmalert and Grafana, add alert rules for CPU, disk, inode, RAM usage, and host status

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

@@ -0,0 +1,38 @@
+{ config, pkgs, lib, ... }:
+{
+  imports = [
+    ./rules/cpu_usage.nix
+    ./rules/disk_usage.nix
+    ./rules/host_down.nix
+    ./rules/inode_usage.nix
+    ./rules/ram_usage.nix
+  ];
+
+  # Standard vmalert service configuration
+  services.vmalert = {
+    enable = true;
+    settings = {
+      "datasource.url" = "http://localhost:8428"; # VictoriaMetrics address
+      "notifier.url" = [ "http://localhost:3001/api/alertmanager/grafana/api/v2/alerts" ]; # Must be a list of strings
+    };
+    # 'rules' is now set by the mkMerge block above.
+  };
+
+  # Override the User and Group for the systemd service managed by the official vmalert module.
+  systemd.services.vmalert = {
+    serviceConfig = {
+      User = "victoriametrics";
+      Group = "victoriametrics";
+    };
+  };
+
+  # Ensure the user/group itself exists on the system.
+  users.users.victoriametrics = lib.mkIf (config.services.victoriametrics.enable || config.services.vmalert.enable) {
+    isSystemUser = true;
+    group = "victoriametrics"; # Primary group for the user
+    home = "/var/lib/victoriametrics"; # Standard home for VictoriaMetrics components
+  };
+  users.groups.victoriametrics = lib.mkIf (config.services.victoriametrics.enable || config.services.vmalert.enable) {
+    # Ensures the group exists.
+  };
+}