nix eval --impure --expr 'let nixpkgs = builtins.getFlake "nixpkgs"; lib = nixpkgs.lib; pkgs = nixpkgs.legacyPackages.x86_64-linux; systemCfg = lib.nixosSystem {
  system = "x86_64-linux";
  modules = [ ./nix/modules/nix-nos/topology.nix ./nix/modules/first-boot-automation.nix {
    networking.hostName = "node01";
    nix-nos.enable = true;
    nix-nos.clusters.plasmacloud = {
      name = "plasmacloud";
      bootstrapNode = null;
      nodes.node01 = { role = "control-plane"; ip = "10.0.1.10"; services = [ "chainfire" ]; };
    };
    services.first-boot-automation = {
      enable = true;
      useNixNOS = true;
      nixnosClusterName = "plasmacloud";
      configFile = "/etc/nixos/secrets/cluster-config.json";
    };
  } ];
}; in systemCfg.config.environment.etc."nixos/secrets/cluster-config.json".text'

Output:
{"bootstrap":true,"cluster_name":"plasmacloud","flaredb_peers":["10.0.1.10:2479"],"initial_peers":[{"addr":"10.0.1.10:2380","id":"node01"}],"leader_url":"https://10.0.1.10:2379","metadata":{},"node_id":"node01","node_role":"control-plane","raft_addr":"10.0.1.10:2380","services":["chainfire"]}