You can write a async function, where you can put all startup codes snippet and make sure you load env variables at very top. You can take reference of below code snippet

```

const express = require('express');

app = express();

async function main() {

// await to load env variables from secret manager

app.listen(PORT, () => { console.log('server started') });

}

main().catch(err => { throw err; })

```

I have not checked syntax of above code. But hope this solve your problem.