Actually we can do it all from a single package.nix

nix/package.nix

@@ -0,0 +1,20 @@
+{pkgs}: let
+  oott-backend = pkgs.rustPlatform.buildRustPackage rec {
+    pname = "oott-backend";
+    version = "0.0.1";
+    src = ./../backend;
+    cargoLock = {
+      lockFile = ./../backend/Cargo.lock;
+    };
+
+    nativeBuildInputs = [pkgs.pkg-config];
+    PKG_CONFIG_PATH = "${pkgs.openssl.dev}/lib/pkgconfig";
+  };
+in
+  pkgs.stdenv.mkDerivation {
+    name = "oott";
+    buildInputs = [oott-backend];
+    installPhase = ''
+      cp ${oott-backend}/bin/* $out/bin/
+    '';
+  }