With this method you can package any type of Next.js App including Apps w/ SSR, API Routes, Server Actions and Proxy (Middleware).

Prerequisites

Obviously Git
Your Next.js App remote Repository w/ package.json and package-lock.json
Your NixOS Server

Getting started

Add the required output mode to your next.config.ts:

import type { NextConfig } from "next";

const nextConfig: NextConfig = {
    output: "standalone",
};

export default nextConfig;

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Your npmDepsHash is the unique id of your package-lock.json. We will need it for the next step, so prefetch it:

nix run --extra-experimental-features "nix-command flakes" nixpkgs#prefetch-npm-deps package-lock.json

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Create your own flake.nix in the same directory as the package.json, make sure to edit the generic "Your Next.js App" Labels and insert your prefetched npmDepsHash from the last step:

{
  description = "Your Next.js App Description";

  # Feel free to choose the input channel yourself 
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };

  outputs = { self, nixpkgs }:
    let
      # Support all Nix-capable Systems
      supportedSystems = [
        "x86_64-linux"   # Standard Intel/AMD Linux
        "aarch64-linux"  # ARM Linux
        "x86_64-darwin"  # Intel Macs
        "aarch64-darwin" # Apple Silicon Macs
      ];

      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
    in {
      packages = forAllSystems (system:
        let
          pkgs = nixpkgs.legacyPackages.${system};
        in {
          default = pkgs.buildNpmPackage {
            pname = "your-nextjs-app";
            version = "1.0.0";
            src = ./.;

            # Insert your prefetched npmDepsHash from the last step
            npmDepsHash = "sha256-...";

            postBuild = ''
              cp -r public .next/standalone/
              cp -r .next/static .next/standalone/.next/
            '';

            installPhase = ''
              cp -r .next/standalone $out
            '';
          };
        }
      );

      nixosModules.default = { config, lib, pkgs, ... }:
        let
          cfg = config.services.your-nextjs-app;

          basePackage = self.packages.${pkgs.system}.default;

          customPackage = basePackage.overrideAttrs (oldAttrs: cfg.environment);
        in {
          options.services.your-nextjs-app = {
            enable = lib.mkEnableOption "Your Next.js App";

            environment = lib.mkOption {
              type = lib.types.attrsOf lib.types.str;
              default = {};
              description = "Key-Value Pairs for Build-Time and Run-Time";
              example = {
                PORT = "3000";
                NODE_ENV = "production";
              };
            };
          };

          config = lib.mkIf cfg.enable {
            systemd.services.your-nextjs-app = {
              description = "Your Next.js App Service";
              wantedBy = [ "multi-user.target" ];
              after = [ "network.target" ];

              environment = cfg.environment;

              serviceConfig = {
                ExecStart = "${pkgs.nodejs_24}/bin/node ${customPackage}/server.js";
                Restart = "always";
              };
            };
          };
        };
    };
}

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With every package update and newly added package to your Next.js App you will need to prefetch your npmDepsHash again (repeat step 2) and update your flake.nix.

Generate your flake.lock for reproducitbility, commit and push:

nix flake lock --extra-experimental-features "nix-command flakes" && git commit -m "Added flake.nix and flake.lock" && git push

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Update your NixOS Server. Example minimal NixOS Build Flake, keep in mind to replace all generic values:

{
  description = "Your NixOS Server";

  # Feel free to choose the input channel yourself
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    your-nextjs-app.url = "github:YourUsername/YourRepository"; 
    # Example input with Codeberg SSH: 
    # "git+ssh://git@codeberg.org/YourUsername/YourRepository.git"
  };

  outputs = { self, nixpkgs, your-nextjs-app, ... }:
    {
      nixosConfigurations = {
        "your-hostname-x86_64" = nixpkgs.lib.nixosSystem {
          system = "x86_64-linux";
          modules = [ configuration.nix ];
        };

        "your-hostname-aarch64" = nixpkgs.lib.nixosSystem {
          system = "aarch64-linux";
          modules = [ configuration.nix ];
        };
      };
    };
}

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Use the provided Service of your Package. Example minimal configuration.nix in the same directory as flake.nix from step 5, keep in mind to replace all generic values:

{ config, pkgs, lib, ... }:
{
  # Demo User feel free to insert your own
  users.users."your-user" = {
      isNormalUser = true;
      initialPassword = "changeme";
      extraGroups = [ "wheel" ];
      openssh.authorizedKeys.keys = "Your .pub SSH Key";
    };

  services.your-nextjs-app = {
    enable = true;

    # Define all environment variables your App needs
    environment = {
      PORT = "3000";
      NODE_ENV = "production";
    };
  };

  networking = {
    hostname = "your-hostname";

    firewall = {
      enable = true;

      # Open the Port used by your Next.js App
      allowedTCPPorts = [ 3000 ];
    };
}

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Rebuild your NixOS System, keep in mind to replace all generic values:

nixos-rebuild switch --flake /path/to/flakeAndConf#<your-hostname-x86_64> or <your-hostname-aarch64> --extra-experimental-features "nix-command flakes"

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Now the your Next.js App should be available as a Service on your NixOS Server. Enjoy <3