Express: does cors configuration depend on server TTL? - node.js

Question

I've successfully deployed my Express API app to AWS elastic beanstalk. I have a React front end that is hosted on S3.
Both are on the same domain with the front end being at example.com & the API at api.example.com
Both have certificates and are secured.
const express = require('express');
const cors = require('cors')({
Origin: 'https://example.com'
});
// followed by required middleware
app.use(cors());
//followed by app constants
app.use((e, req, res, next) => {
res.header("Access-Control-Allow-Origin", "https://example.com");
res.header('Access-Control-Allow-Methods', 'DELETE, PUT, GET, POST');
res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
if (e) {
console.log(e);
res.status(500).send(e.message);
}
next();
})
// followed by app routes
When I try and register a user on my site, I get the error:
Access to XMLHttpRequest at 'https://api.example.com/users/signup/' from origin 'https://example.com' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.
This topic has of course been covered multiple times on Stack Overflow (which I've gone through multiple solutions this morning), but my question has to do with the actual server where the API is being hosted.
In the hosted zone for api.example.com, it has a TTL of 172800(48 hours). Does this mean that my changes won't be reflected in that time? If that is the case, does this mean that every time you deploy code it resets the TTL?
I'm a front end dev working on a side project, so this really isn't my area of expertise. Any DevOps or BackEnd Devs have any ideas? Thanks in advance!

Answer 1

In the hosted zone for api.example.com, it has a TTL of 172800(48 hours). Does this mean that my changes won't be reflected in that time? If that is the case, does this mean that every time you deploy code it resets the TTL?
No.
The TTL is how long other DNS servers are expected to cache the DNS information (e.g. which server the domain name points to).
It has nothing to do with deployment of code.
Your problem is unrelated to that. I'd add some logging to the server-side code to see which routes and middleware were actually hit as well as monitoring the precise request and response you are getting in the Network tab of your browser.

Answer 2

There a preflight OPTIONS request can be made by the browser for the particular types of cross-domain requests. If the response on that request is not successful or doesn't have CORS headers you will also get such error.
So I suppose that you should add a route in your Express app to handle preflight requests and send back the same CORS headers or just use express-cors-middleware.