server.js

const fs = require("fs");
const { createServer } = require("http");
const path = require("path");

const { createRequestHandler } = require("@remix-run/express");
const compression = require("compression");
const express = require("express");
const morgan = require("morgan");

const MODE = process.env.NODE_ENV;
const BUILD_DIR = path.join(process.cwd(), "build");

if (!fs.existsSync(BUILD_DIR)) {
  console.warn(
    "Build directory doesn't exist, please run `npm run dev` or `npm run build` before starting the server."
  );
}

const app = express();

// You need to create the HTTP server from the Express app
const httpServer = createServer(app);

app.use(compression());

// You may want to be more aggressive with this caching
app.use(express.static("public", { maxAge: "1h" }));

// Remix fingerprints its assets so we can cache forever
app.use(express.static("public/build", { immutable: true, maxAge: "1y" }));

app.use(morgan("tiny"));
app.all(
  "*",
  MODE === "production"
    ? createRequestHandler({ build: require("./build") })
    : (req, res, next) => {
        purgeRequireCache();
        const build = require("./build");
        return createRequestHandler({ build, mode: MODE })(req, res, next);
      }
);

const port = process.env.PORT || 3000;

// instead of running listen on the Express app, do it on the HTTP server
httpServer.listen(port, () => {
  console.log(`Express server listening on port ${port}`);
});

function purgeRequireCache() {
  for (const key in require.cache) {
    if (key.startsWith(BUILD_DIR)) {
      delete require.cache[key];
    }
  }
}