nixos/promtail: Add a promtail module

nixos/modules/module-list.nix

@@ -394,6 +394,7 @@
   ./services/logging/logcheck.nix
   ./services/logging/logrotate.nix
   ./services/logging/logstash.nix
+  ./services/logging/promtail.nix
   ./services/logging/rsyslogd.nix
   ./services/logging/syslog-ng.nix
   ./services/logging/syslogd.nix

nixos/modules/services/logging/promtail.nix

@@ -0,0 +1,95 @@
+{ config, lib, pkgs, ... }: with lib;
+let
+  cfg = config.services.promtail;
+
+  prettyJSON = conf: pkgs.runCommandLocal "promtail-config.json" {} ''
+    echo '${builtins.toJSON conf}' | ${pkgs.buildPackages.jq}/bin/jq 'del(._module)' > $out
+  '';
+
+in {
+  options.services.promtail = with types; {
+    enable = mkEnableOption "the Promtail ingresser";
+
+    configuration = mkOption {
+      type = with lib.types; let
+        valueType = nullOr (oneOf [
+          bool
+          int
+          float
+          str
+          (lazyAttrsOf valueType)
+          (listOf valueType)
+        ]) // {
+          description = "JSON value";
+          emptyValue.value = {};
+          deprecationMessage = null;
+        };
+      in valueType;
+      description = ''
+        Specify the configuration for Promtail in Nix.
+      '';
+    };
+
+    extraFlags = mkOption {
+      type = listOf str;
+      default = [];
+      example = [ "--server.http-listen-port=3101" ];
+      description = ''
+        Specify a list of additional command line flags,
+        which get escaped and are then passed to Loki.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    services.promtail.configuration.positions.filename = mkDefault "/var/cache/promtail/positions.yaml";
+
+    systemd.services.promtail = {
+      description = "Promtail log ingress";
+      wantedBy = [ "multi-user.target" ];
+      stopIfChanged = false;
+
+      serviceConfig = {
+        Restart = "on-failure";
+
+        ExecStart = "${pkgs.grafana-loki}/bin/promtail -config.file=${prettyJSON cfg.configuration} ${escapeShellArgs cfg.extraFlags}";
+
+        ProtectSystem = "strict";
+        ProtectHome = true;
+        PrivateTmp = true;
+        PrivateDevices = true;
+        ProtectKernelTunables = true;
+        ProtectControlGroups = true;
+        RestrictSUIDSGID = true;
+        PrivateMounts = true;
+        CacheDirectory = "promtail";
+
+        User = "promtail";
+        Group = "promtail";
+
+        CapabilityBoundingSet = "";
+        NoNewPrivileges = true;
+
+        ProtectKernelModules = true;
+        SystemCallArchitectures = "native";
+        ProtectKernelLogs = true;
+        ProtectClock = true;
+
+        LockPersonality = true;
+        ProtectHostname = true;
+        RestrictRealtime = true;
+        MemoryDenyWriteExecute = true;
+        PrivateUsers = true;
+      } // (optionalAttrs (!pkgs.stdenv.isAarch64) { # FIXME: figure out why this breaks on aarch64
+        SystemCallFilter = "@system-service";
+      });
+    };
+
+    users.groups.promtail = {};
+    users.users.promtail = {
+      description = "Promtail service user";
+      isSystemUser = true;
+      group = "promtail";
+    };
+  };
+}

nixos/tests/loki.nix

@@ -12,15 +12,28 @@ import ./make-test-python.nix ({ lib, pkgs, ... }:
       enable = true;
       configFile = "${pkgs.grafana-loki.src}/cmd/loki/loki-local-config.yaml";
     };
-    systemd.services.promtail = {
-      description = "Promtail service for Loki test";
-      wantedBy = [ "multi-user.target" ];
-
-      serviceConfig = {
-        ExecStart = ''
-          ${pkgs.grafana-loki}/bin/promtail --config.file ${pkgs.grafana-loki.src}/cmd/promtail/promtail-local-config.yaml
-        '';
-        DynamicUser = true;
+    services.promtail = {
+      enable = true;
+      configuration = {
+        server = {
+          http_listen_port = 9080;
+          grpc_listen_port = 0;
+        };
+        clients = [ { url = "http://localhost:3100/loki/api/v1/push"; } ];
+        scrape_configs = [
+          {
+            job_name = "system";
+            static_configs = [
+              {
+                targets = [ "localhost" ];
+                labels = {
+                  job = "varlogs";
+                  __path__ = "/var/log/*log";
+                };
+              }
+            ];
+          }
+        ];
       };
     };
   };