prometheus-snmp-exporter: added nixos module

nixos/modules/services/monitoring/prometheus/snmp-exporter.nix

@@ -0,0 +1,127 @@
+{ config, pkgs, lib, ... }:
+
+with lib;
+
+let
+  cfg = config.services.prometheus.snmpExporter;
+  mkConfigFile = pkgs.writeText "snmp.yml" (if cfg.configurationPath == null then builtins.toJSON cfg.configuration else builtins.readFile cfg.configurationPath);
+in {
+  options = {
+    services.prometheus.snmpExporter = {
+      enable = mkEnableOption "Prometheus snmp exporter";
+
+      user = mkOption {
+        type = types.str;
+        default = "nobody";
+        description = ''
+          User name under which snmp exporter shall be run.
+        '';
+      };
+
+      group = mkOption {
+        type = types.str;
+        default = "nogroup";
+        description = ''
+          Group under which snmp exporter shall be run.
+        '';
+      };
+
+      port = mkOption {
+        type = types.int;
+        default = 9116;
+        description = ''
+          Port to listen on.
+        '';
+      };
+
+      listenAddress = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        description = ''
+          Address to listen on for web interface and telemetry.
+        '';
+      };
+
+      configurationPath = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        description = ''
+          Path to a snmp exporter configuration file. Mutually exclusive with 'configuration' option.
+        '';
+        example = "./snmp.yml";
+      };
+
+      configuration = mkOption {
+        type = types.nullOr types.attrs;
+        default = {};
+        description = ''
+          Snmp exporter configuration as nix attribute set. Mutually exclusive with 'configurationPath' option.
+        '';
+        example = ''
+          {
+            "default" = {
+              "version" = 2;
+              "auth" = {
+                "community" = "public";
+              };
+            };
+          };
+        '';
+      };
+
+      logFormat = mkOption {
+        type = types.str;
+        default = "logger:stderr";
+        description = ''
+          Set the log target and format.
+        '';
+      };
+
+      logLevel = mkOption {
+        type = types.enum ["debug" "info" "warn" "error" "fatal"];
+        default = "info";
+        description = ''
+          Only log messages with the given severity or above.
+        '';
+      };
+
+      openFirewall = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          Open port in firewall for incoming connections.
+        '';
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    networking.firewall.allowedTCPPorts = optional cfg.openFirewall cfg.port;
+
+    assertions = singleton
+      {
+        assertion = (cfg.configurationPath == null) != (cfg.configuration == null);
+        message = "Please ensure you have either 'configuration' or 'configurationPath' set!";
+      };
+
+    systemd.services.prometheus-snmp-exporter = {
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network.target" ];
+      script = ''
+        ${pkgs.prometheus-snmp-exporter.bin}/bin/snmp_exporter \
+          -config.file ${mkConfigFile} \
+          -log.format ${cfg.logFormat} \
+          -log.level ${cfg.logLevel} \
+          -web.listen-address ${optionalString (cfg.listenAddress != null) cfg.listenAddress}:${toString cfg.port}
+      '';
+
+      serviceConfig = {
+        User = cfg.user;
+        Group = cfg.group;
+        Restart  = "always";
+        PrivateTmp = true;
+        WorkingDirectory = "/tmp";
+      };
+    };
+  };
+}