feat(k3s-node): Add k3s-node role and enable on john-endesktop

Add reusable k3s-node role with configurable options for server/agent
modes. Configure john-endesktop as a k3s agent joining the cluster at
10.0.0.222.

Role supports:
- Server or agent role selection
- Configurable server address and token file
- Graceful node shutdown
- Optional firewall port opening
- Cluster initialization for first server

Note: NixOS nodes must be labeled with `k3s-upgrade=disabled` to exclude
them from the system-upgrade-controller, since NixOS manages k3s upgrades
through Nix rather than in-place binary replacement.

machines/john-endesktop/configuration.nix

@@ -104,6 +104,14 @@ with lib;
   # User configuration
   roles.users.enable = true;
 
+  # k3s agent configuration
+  roles.k3s-node = {
+    enable = true;
+    role = "agent";
+    # serverAddr defaults to https://10.0.0.222:6443
+    # tokenFile defaults to /etc/k3s/token
+  };
+
   # Time zone
   time.timeZone = "America/Los_Angeles"; # Adjust as needed
 

roles/default.nix

@@ -9,6 +9,7 @@ with lib;
     ./bluetooth
     ./btrfs
     ./desktop
+    ./k3s-node
     ./kodi
     ./nfs-mounts
     ./nvidia

roles/k3s-node/default.nix

@@ -0,0 +1,81 @@
+{ lib, config, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.roles.k3s-node;
+in
+{
+  options.roles.k3s-node = {
+    enable = mkEnableOption "Enable k3s node";
+
+    role = mkOption {
+      type = types.enum [ "server" "agent" ];
+      default = "agent";
+      description = "k3s role: server (control plane) or agent (worker)";
+    };
+
+    serverAddr = mkOption {
+      type = types.str;
+      default = "https://10.0.0.222:6443";
+      description = "URL of k3s server to join (required for agents, used for HA servers)";
+    };
+
+    tokenFile = mkOption {
+      type = types.path;
+      default = "/etc/k3s/token";
+      description = "Path to file containing the cluster join token";
+    };
+
+    clusterInit = mkOption {
+      type = types.bool;
+      default = false;
+      description = "Initialize a new cluster (first server only)";
+    };
+
+    extraFlags = mkOption {
+      type = types.listOf types.str;
+      default = [];
+      description = "Additional flags to pass to k3s";
+    };
+
+    gracefulNodeShutdown = mkOption {
+      type = types.bool;
+      default = true;
+      description = "Enable graceful node shutdown";
+    };
+
+    openFirewall = mkOption {
+      type = types.bool;
+      default = true;
+      description = "Open firewall ports for k3s";
+    };
+  };
+
+  config = mkIf cfg.enable {
+    # k3s service configuration
+    services.k3s = {
+      enable = true;
+      role = cfg.role;
+      tokenFile = cfg.tokenFile;
+      extraFlags = cfg.extraFlags;
+      gracefulNodeShutdown.enable = cfg.gracefulNodeShutdown;
+      serverAddr = if (cfg.role == "agent" || !cfg.clusterInit) then cfg.serverAddr else "";
+      clusterInit = cfg.role == "server" && cfg.clusterInit;
+    };
+
+    # Firewall rules for k3s
+    networking.firewall = mkIf cfg.openFirewall {
+      allowedTCPPorts = [
+        6443  # k3s API server
+        10250 # kubelet metrics
+      ] ++ optionals (cfg.role == "server") [
+        2379  # etcd clients (HA)
+        2380  # etcd peers (HA)
+      ];
+      allowedUDPPorts = [
+        8472  # flannel VXLAN
+      ];
+    };
+  };
+}