nixos/services.kubernetes.kubelet: handle non-lower case characters in hostname

nixos/doc/manual/release-notes/rl-2411.section.md

@@ -112,6 +112,10 @@
   services.portunus.ldap.package = pkgs.openldap.override { libxcrypt = pkgs.libxcrypt-legacy; };
   ```
 
+- The default value of `services.kubernetes.kubelet.hostname` is now lowercased.
+  Explicitly set `kubelet.hostname` to `networking.fqdnOrHostName` to get back
+  the old default behavior.
+
 - `keycloak` was updated to version 25, which introduces new hostname related options.
   See [Upgrading Guide](https://www.keycloak.org/docs/25.0.1/upgrading/#migrating-to-25-0-0) for instructions.
 

nixos/modules/services/cluster/kubernetes/kubelet.nix

@@ -356,7 +356,7 @@ in
       boot.kernelModules = ["br_netfilter" "overlay"];
 
       services.kubernetes.kubelet.hostname =
-        mkDefault config.networking.fqdnOrHostName;
+        mkDefault (lib.toLower config.networking.fqdnOrHostName);
 
       services.kubernetes.pki.certs = with top.lib; {
         kubelet = mkCert {