prometheus: modular exporter module

modules/prometheus/default.nix

@@ -0,0 +1,100 @@
+{
+  config,
+  lib,
+  ...
+}:
+
+let
+  cfg = config.ocf.prometheus-export;
+in
+{
+  options.ocf.prometheus-export = {
+    enable = lib.mkEnableOption "exporting prometheus data";
+    textFileDir = lib.mkOption {
+      type = lib.types.str;
+      default = "/var/lib/node_exporter/textfile_collector";
+    };
+    exporters = lib.mkOption {
+      default = { };
+      type = lib.types.attrsOf lib.types.submodule {
+        enable = lib.mkEnableOption "running this exporter";
+        script = lib.mkOption {
+          type = lib.types.package;
+          description = "the script to execute, the textfile to write is passed as argv[1]";
+        };
+        interval = lib.mkOption {
+          type = lib.types.str;
+          description = "how often to run the script, use systemd format (ex: '5s')";
+          default = "5s";
+        };
+        serviceName = lib.mkOption {
+          type = lib.types.str;
+        };
+      };
+    };
+  };
+
+  config = lib.mkMerge [
+    lib.mkIf
+    cfg.enable
+    (
+      lib.mkMerge (
+        lib.mapAttrsToList (
+          name: exporter:
+          let
+            serviceName = "prometheus-textfile-exporter-${name}";
+          in
+          {
+            cfg.exporters."${name}".serviceName = serviceName;
+            systemd.services."${serviceName}" = {
+              enable = true;
+              after = [ "network.target" ];
+              wants = [ "network.target" ];
+              wantedBy = [ "multi-user.target" ];
+
+              serviceConfig = {
+                Type = "oneshot";
+                User = "root";
+                ExecStart = "${lib.getExe exporter.script} ${cfg.textFileDir}/${name}.prom";
+              };
+            };
+            systemd.timers."${serviceName}" = {
+              wantedBy = [ "timers.target" ];
+              timerConfig = {
+                OnUnitActiveSec = exporter.interval;
+                AccuracySec = "1ms";
+                Unit = "${serviceName}.service";
+              };
+            };
+          }
+        ) cfg.exporters
+      )
+      // {
+        systemd.tmpfiles.rules = [
+          "d ${cfg.textFileDir} 0755 root root -"
+        ];
+
+        services.prometheus = {
+          exporters = {
+            node = {
+              enable = true;
+              port = 9100;
+              openFirewall = true;
+              enabledCollectors = [
+                "systemd"
+                "textfile"
+                "ethtool"
+                "softirqs"
+                "tcpstat"
+                "wifi"
+              ];
+              extraFlags = [
+                "--collector.textfile.directory=${cfg.textFileDir}"
+              ];
+            };
+          };
+        };
+      }
+    )
+  ];
+}

modules/prometheus/logged-in-users-exporter.nix

@@ -0,0 +1,46 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+
+let
+  cfg = config.ocf.logged-in-users-exporter;
+  prom = config.ocf.prometheus-export;
+in
+{
+  options.ocf.logged-in-users-exporter.enable = lib.mkEnableOption "logged in users exporter";
+  config = lib.mkIf cfg.enable {
+    prom.textFileScripts = lib.singleton pkgs.writeShellScriptBin "logged-in-users-exporter" ''
+      output_file="${prom.textFileDir}/logged_in_users.prom"
+
+      # clear and reset the file, then add anyone who is logged in
+      > "$output_file"
+      loginctl list-sessions --no-legend | while read -r session_id uid user seat leader class tty idle since; do
+      if [[ $class == "user" ]] && [[ $seat == "seat0" ]] && [[ $idle == "no" ]]; then
+          # we only want to list users who are:
+          # - online: logged in but not in the foreground
+          # - active: logged in and in the foreground
+          # TODO: list logged in users but dont place a penguin if no sessions are active
+          session_status=$(loginctl show-session "$session_id" -p State --value)
+          if ! [[ $session_status == "online" || $session_status == "active" ]]; then
+          continue
+          fi
+
+          # If the locking program supports systemd-logind, LockedHint can checked instead.
+          # To support lockers that do not support logind, locked_status is only set to
+          # locked if LockedHint specifically says so.
+          session_lockedhint=$(loginctl show-session "$session_id" -p LockedHint --value)
+          if [[ $session_lockedhint == "yes" ]]; then
+          locked_status="locked"
+          else
+          locked_status="unlocked"
+          fi
+
+          # TODO: allow multiple users to be listed as logged in on a computer
+          echo "node_logged_in_user{name=\"$user\", state=\"$locked_status\"} 1" > "$output_file"
+      fi
+    '';
+  };
+}

profiles/desktop.nix

@@ -16,6 +16,7 @@
     home.tmpfs = true;
     home.mountRemote = true;
     network.wakeOnLan.enable = true;
+    prometheus-export.enable = true;
     logged-in-users-exporter.enable = true;
 
     zfs.enable = true;