Use mkIf cfg.enable pattern

Should be pure refactoring

morph/lib/base.nix

@@ -62,6 +62,8 @@
       "172.23.23.1" = [ "monitoring" "monitoring.monitoringvpn" ];
     };
 
+    services.private-storage.monitoring.exporters.promtail.enable = true;
+
     assertions = [
       # This is a check to save somebody in the future trying to debug why
       # setting `nixpkgs.config` is not having an effect.

morph/lib/issuer.nix

@@ -8,7 +8,6 @@ in {
   imports = [
     ../../nixos/modules/monitoring/vpn/client.nix
     ../../nixos/modules/monitoring/exporters/node.nix
-    ../../nixos/modules/monitoring/exporters/promtail.nix
   ];
 
   options.grid.issuer = {

morph/lib/monitoring.nix

@@ -33,7 +33,6 @@ in {
     ../../nixos/modules/monitoring/server/loki.nix
     ../../nixos/modules/monitoring/exporters/node.nix
     ../../nixos/modules/monitoring/exporters/blackbox.nix
-    ../../nixos/modules/monitoring/exporters/promtail.nix
   ];
 
   options.grid.monitoring = {

morph/lib/storage.nix

@@ -15,8 +15,6 @@ in {
     ../../nixos/modules/monitoring/exporters/node.nix
     # Collect Tahoe OpenMetrics statistics.
     ../../nixos/modules/monitoring/exporters/tahoe.nix
-    # Send logs to central logging server.
-    ../../nixos/modules/monitoring/exporters/promtail.nix
   ];
 
   options.grid.storage = {

nixos/modules/default.nix

@@ -12,5 +12,6 @@
   imports = [
     ./packages.nix
     ./issuer.nix
+    ./monitoring/exporters/promtail.nix
   ];
 }

nixos/modules/monitoring/exporters/promtail.nix

@@ -6,15 +6,21 @@
 #              exporters, but it is very similar in what it is doing -
 #              preparing local data and sending it off to a TSDB.
 
-{ config, ... }:
+{ config, options, lib, ... }:
 
 let
+  cfg = config.services.private-storage.monitoring.exporters.promtail;
   hostName = config.networking.hostName;
 
 in {
-  config.services.promtail.enable = true;
-  config.networking.firewall.interfaces.monitoringvpn.allowedTCPPorts = [ 9080 ];
-  config.services.promtail.configuration = {
+  options.services.private-storage.monitoring.exporters.promtail = {
+    enable = lib.mkEnableOption "Promtail log exporter service";
+  };
+
+  config = lib.mkIf cfg.enable {
+    services.promtail.enable = true;
+    networking.firewall.interfaces.monitoringvpn.allowedTCPPorts = [ 9080 ];
+    services.promtail.configuration = {
       server = {
         http_listen_port = 9080; # Using /metrics for health check
         grpc_listen_address = "127.0.0.1"; # unused, but no option to turn it off.
@@ -39,4 +45,5 @@ in {
         }];
       }];
     };
+  };
 }