alloy: Actually implement the functionality

modules/system/services/alloy.nix

@@ -13,6 +13,18 @@ in
       type = lib.types.port;
       default = 12345;
     };
+    metricsEndpoint = lib.mkOption {
+      type = lib.types.nonEmptyStr;
+      default = "https://metrics.${config.custom.services.tailscale.domain}/prometheus/api/v1/write";
+    };
+    logsEndpoint = lib.mkOption {
+      type = lib.types.nonEmptyStr;
+      default = "https://logs.${config.custom.services.tailscale.domain}/insert/loki/api/v1/push";
+    };
+    collect = {
+      hostMetrics = lib.mkEnableOption "";
+      sshdLogs = lib.mkEnableOption "";
+    };
   };
 
   config = lib.mkIf cfg.enable {
@@ -28,5 +40,44 @@ in
         "--disable-reporting"
       ];
     };
+
+    environment.etc = {
+      "alloy/endpoints.alloy".text = ''
+        prometheus.remote_write "default" {
+          endpoint {
+            url = "${cfg.metricsEndpoint}"
+          }
+        }
+
+        loki.write "default" {
+          endpoint {
+            url = "${cfg.logsEndpoint}"
+          }
+        }
+      '';
+
+      "alloy/node-exporter.alloy" = lib.mkIf cfg.collect.hostMetrics {
+        text = ''
+          prometheus.exporter.unix "default" {
+            enable_collectors = [ "systemd" ]
+          }
+
+          prometheus.scrape "node_exporter" {
+            targets = prometheus.exporter.unix.default.targets
+            forward_to = [prometheus.remote_write.default.receiver]
+            scrape_interval = "15s"
+          }
+        '';
+      };
+
+      "alloy/sshd-logs.alloy" = lib.mkIf cfg.collect.sshdLogs {
+        text = ''
+          loki.source.journal "sshd" {
+            matches = "_SYSTEMD_UNIT=sshd.service"
+            forward_to = [loki.write.default.receiver]
+          }
+        '';
+      };
+    };
   };
 }