Use log retention setting in promtail and loki config

nixos/modules/monitoring/exporters/promtail.nix

@@ -11,6 +11,7 @@
 let
   cfg = config.services.private-storage.monitoring.exporters.promtail;
   hostName = config.networking.hostName;
+  logRetention = toString(config.services.private-storage.monitoring.policy.logRetentionSeconds) + "s";
 
 in {
   options.services.private-storage.monitoring.exporters.promtail = {
@@ -40,7 +41,7 @@ in {
     services.journald.extraConfig = ''
       # This tells journald it can discard log files that contain only log
       # entries that are older than 29 days.
-      MaxRetentionSec=29day
+      MaxRetentionSec=${logRetention}
 
       # This tells journald to start a new log file once a day.  Together with
       # the MaxRetentionSec setting, this means that entries are kept for

nixos/modules/monitoring/server/loki.nix

@@ -7,7 +7,11 @@
 #     https://grafana.com/docs/loki/latest/configuration/examples/#complete-local-configyaml
 #
 
-{
+{ config, ...}:
+let
+  logRetention = toString(config.services.private-storage.monitoring.policy.logRetentionSeconds) + "s";
+
+in {
   config.networking.firewall.interfaces.monitoringvpn.allowedTCPPorts = [ 3100 ];
 
   config.services.loki = {
@@ -61,7 +65,7 @@
 
         table_manager = {
           retention_deletes_enabled = true;
-          retention_period = "336h"; # two weeks
+          retention_period = logRetention;
         };
       };
   };