initial observability setup

modules/nixos/services/observability/promtail/default.nix

@@ -0,0 +1,56 @@
+{ pkgs, config, lib, namespace, ... }:
+let
+  inherit (lib.modules) mkIf;
+  inherit (lib.options) mkEnableOption;
+
+  cfg = config.${namespace}.services.observability.promtail;
+in
+{
+  options.${namespace}.services.observability.promtail = {
+    enable = mkEnableOption "enable Grafana Promtail";
+  };
+
+  config = mkIf cfg.enable {
+    services.promtail = {
+      enable = true;
+
+      # Ensures proper permissions
+      extraFlags = [
+        "-config.expand-env=true"
+      ];
+
+      configuration = {
+        server = {
+          http_listen_port = 9004;
+          grpc_listen_port = 0;
+        };
+
+        positions = {
+          filename = "filename";
+        };
+
+        clients = {
+          url = "http://127.0.0.1:3100/loki/api/v1/push";
+        };
+
+        scrape_configs = [
+          {
+            job_name = "journal";
+            journal = {
+              max_age = "12h";
+              labels = {
+                job = "systemd-journal";
+                host = "ulmo";
+              };
+            };
+            relabel_configs = [
+              { source_labels = [ "__journal__systemd_unit" ]; target_label = "unit"; }
+            ];
+          }
+        ];
+      };
+    };
+    
+    networking.firewall.allowedTCPPorts = [ 9004 ];
+  };
+}