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Super slow preflight OPTIONS in Chrome only

Posted by: admin November 30, 2017 Leave a comment


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).

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.

2 requests, OPTIONS takes 3 seconds

Most of this time is spent downloading an empty content:

Downloading an empty content takes 3 seconds

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

A few other things I tried:

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

We’re using on the back-end NodeJS with the CORS package.

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

Anyone experienced this too?


Just as a note: It seems a chrome bug

I reproduced the issue using a server with two DNS names using a service in a unique domain

https://domain1.com  --> https://domain1.com (No CORS, no delay)
https://domain2.com  --> https://domain1.com (CORS, delay)

chrome cors

It is exactly the same service responding to two names, so I am testing exactly the same request, client and server code (DNS names are interchangeable)

Tested with

  • Chrome 61.0.3163.100 (Windows) –>DELAY
  • Chrome 62.0.3202.84 (Android) –>DELAY
  • Chrome 62.0.3202.84 (iOS-Ipad) –>OK!!!
  • Firefox–>OK
  • Edge –> OK

Workaround (in my case). Create a proxy in my host to respond to the same origin DNS and avoid CORS