config_subset.nix

  # Commented-out is a minimal example of what works, uncommented has an internal error
  
  services.uwsgi.enable = true;
  services.uwsgi.plugins = [ "python3" ];
  # services.uwsgi.instance = {
  #   type = "emperor";
  #   vassals.hello = {
  #     type = "normal";
  #     master = true;
  #     workers = 2;
  #     http = ":8000";
  #     module = "wsgi:application";
  #     chdir = path/to/app;
  #     pythonPackages = self: with self; [ flask ];
  #   };
  # };
  services.uwsgi.instance = {
    type = "emperor";
    vassals.hello = {
      type = "normal";
      master = true;
      workers = 2;
      http = ":8000";
      module = "wsgi:application";
      chdir = path/to/app;
      pythonPackages = self: with self; let
        src = pkgs.fetchFromGitHub {
          owner = "nix-community";
          repo = "poetry2nix";
          rev = "e7c69a288c10e4d97816fdabda5ae3f38e21914e";
          sha256 = "1sygililyh44igkj57ihyv1i0kjmj646nw80q1jrj9pvs8m97hgm";
        };
      in
      with import "${src.out}/overlay.nix" pkgs pkgs;
      [
        poetry2nix.mkPoetryApplication {
          projectDir = path/to/app;
        }
      ];
    };
  };

shell.nix

with import <nixpkgs> {};
let
  src = fetchFromGitHub {
    owner = "nix-community";
    repo = "poetry2nix";
    rev = "e7c69a288c10e4d97816fdabda5ae3f38e21914e";
    sha256 = "1sygililyh44igkj57ihyv1i0kjmj646nw80q1jrj9pvs8m97hgm";
  };
in
  with import "${src.out}/overlay.nix" pkgs pkgs;
  let
    pythonEnv = poetry2nix.mkPoetryEnv {
      projectDir = ./.;
    };
  in
  mkShell {
    name = "dev-environment";

    nativeBuildInputs = [
    ];

    buildInputs = [
      pythonEnv
      pkgs.python37.pkgs.poetry
    ];
  }

syslog

Jun 21 16:47:52 nixos uwsgi[21476]: --- no python application found, check your startup logs for errors ---
Jun 21 16:47:52 nixos uwsgi[21476]: [pid: 21483|app: -1|req: -1/3] 127.0.0.1 () {28 vars in 287 bytes} [Sun Jun 21 16:47:52 2020] GET / => generated 21 bytes in 0 msecs (HTTP/1.1 500) 2 headers in 83 bytes (0 switches on core 0)