grafana: use postgresql

Doesn't use for data, only annotation and other stuff

services/grafana/grafana.nix

@@ -26,6 +26,12 @@
         root_url = "https://${service_configs.grafana.domain}";
       };
 
+      database = {
+        type = "postgres";
+        host = service_configs.postgres.socket;
+        user = "grafana";
+      };
+
       "auth.anonymous" = {
         enabled = true;
         org_role = "Admin";
@@ -83,4 +89,15 @@
     import ${config.age.secrets.caddy_auth.path}
     reverse_proxy :${toString service_configs.ports.private.grafana.port}
   '';
+
+  services.postgresql = {
+    ensureDatabases = [ "grafana" ];
+    ensureUsers = [
+      {
+        name = "grafana";
+        ensureDBOwnership = true;
+        ensureClauses.login = true;
+      }
+    ];
+  };
 }

services/grafana/prometheus.nix

@@ -21,7 +21,7 @@ in
     port = service_configs.ports.private.prometheus.port;
     listenAddress = "127.0.0.1";
     stateDir = "prometheus";
-    retentionTime = "90d";
+    retentionTime = "0d"; # 0 disables time-based retention (keep forever)
 
     exporters = {
       node = {