Super slow preflight OPTIONS in Chrome only : <p>I've been struggling recently with a super-weird problem only happening in Chrome: as my API (NodeJS) is on a different subdomain, I need to use CORS to reach it from my front-end (EmberJS).</p>

<p>It's working pretty well but I'm very frequently (95% of the time) having very very slow OPTIONS queries, delaying any API calls by about 3 seconds.</p>

<p><a href="https://i.stack.imgur.com/59gE1.png" rel="noreferrer"><img src="https://i.stack.imgur.com/59gE1.png" alt="2 requests, OPTIONS takes 3 seconds"></a></p>

<p>Most of this time is spent downloading an empty content:</p>

<p><a href="https://i.stack.imgur.com/y9S1G.png" rel="noreferrer"><img src="https://i.stack.imgur.com/y9S1G.png" alt="Downloading an empty content takes 3 seconds"></a></p>

<p>It gets even weirder when I'm trying this on another website we made using a similar architecture, experiencing the exact same problem.</p>

<p>A few other things I tried:</p>

<ul>
<li>I've been trying this with Firefox and Safari, and didn't get any delay.</li>
<li>I've been trying this locally or in production, experimenting the same delay.</li>
<li>I've been trying this with incognito mode (no extensions), and I have the exact same problem.</li>
</ul>

<p>We're using on the back-end NodeJS with the <a href="https://www.npmjs.com/package/cors" rel="noreferrer">CORS package</a>.</p>

<p>Now, I have no idea if the problem is on either Chrome 60, NodeJS, the CORS package or EmberJS + jQuery.</p>

<p>Anyone experienced this too?</p>
