modules: services: add monitoring

This includes a dashboard to monitor system ressources, using
Prometheus.

modules/services/default.nix

@@ -14,6 +14,7 @@
     ./lohr.nix
     ./matrix.nix
     ./miniflux.nix
+    ./monitoring.nix
     ./nextcloud.nix
     ./nginx.nix
     ./pirate.nix

modules/services/monitoring.nix

@@ -0,0 +1,116 @@
+# Grafana dashboards for all the things!
+{ config, lib, pkgs, ... }:
+let
+  cfg = config.my.services.monitoring;
+
+  domain = config.networking.domain;
+  grafanaDomain = "monitoring.${config.networking.domain}";
+in
+{
+  options.my.services.monitoring = with lib; {
+    enable = mkEnableOption "monitoring";
+
+    grafana = {
+      port = mkOption {
+        type = types.port;
+        default = 9500;
+        example = 3001;
+        description = "Internal port";
+      };
+
+      username = mkOption {
+        type = types.str;
+        default = "ambroisie";
+        example = "admin";
+        description = "Admin username";
+      };
+
+      passwordFile = mkOption {
+        type = types.str;
+        example = "/var/lib/grafana/password.txt";
+        description = "Admin password stored in a file";
+      };
+    };
+
+    prometheus = {
+      port = mkOption {
+        type = types.port;
+        default = 9501;
+        example = 3002;
+        description = "Internal port";
+      };
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    services.grafana = {
+      enable = true;
+      domain = grafanaDomain;
+      port = cfg.grafana.port;
+      addr = "127.0.0.1"; # Proxied through Nginx
+
+      security = {
+        adminUser = cfg.grafana.username;
+        adminPasswordFile = cfg.grafana.passwordFile;
+      };
+
+      provision = {
+        enable = true;
+
+        datasources = [
+          {
+            name = "Prometheus";
+            type = "prometheus";
+            url = "http://localhost:${toString cfg.prometheus.port}";
+          }
+        ];
+
+        dashboards = [
+          {
+            name = "Node Exporter";
+            options.path = pkgs.nur.repos.alarsyo.grafana-dashboards.node-exporter;
+            disableDeletion = true;
+          }
+        ];
+      };
+    };
+
+    services.prometheus = {
+      enable = true;
+      port = cfg.prometheus.port;
+      listenAddress = "127.0.0.1";
+
+      retentionTime = "2y";
+
+      exporters = {
+        node = {
+          enable = true;
+          enabledCollectors = [ "systemd" ];
+          port = 9100;
+          listenAddress = "127.0.0.1";
+        };
+      };
+
+      scrapeConfigs = [
+        {
+          job_name = config.networking.hostName;
+          static_configs = [{
+            targets = [ "127.0.0.1:${toString config.services.prometheus.exporters.node.port}" ];
+          }];
+        }
+      ];
+    };
+
+    services.nginx = {
+      virtualHosts.${grafanaDomain} = {
+        forceSSL = true;
+        useACMEHost = domain;
+
+        locations."/" = {
+          proxyPass = "http://127.0.0.1:${toString cfg.grafana.port}";
+          proxyWebsockets = true;
+        };
+      };
+    };
+  };
+}