I’ve spent the last 30 minutes looking into strange behavior on Github.com with pages failing to be styled. The initial issues pointed to a CORS (cross-origin resource sharing) issue with the browser blocking content hosted on various alternative domains.

These domains exist to have CDN’s (content delivery networks) cache resource files (scripts, images, video, stylesheets or other static or relatively static content) closer to the consumer. This aids in speeding the loading of these resources and generally adds a layer of failure prevention by routing a request to the nearest available system that hosts the content. If the one local to you is down, you should get forwarded on to the next closest and so on.

The CDN services appear to be returning HTTP\503 (service unavailable) errors and not the expected content, causing CORS issues to show up in browsers, image/video content not loading in and the general layout of websites being broken with CSS files failing to download.

I’ve seen reports of Twitter being affected, Fastly is entirely inaccessible for me, even when attempting to connect to different CDN’s by “changing” my location using VPNs.

I’m still having issues with Github and SquareSpace.

UPDATE:

It looks like the CDN that failed was most likely Fastly’s.

Some sites have started to recover from the outage but not all, hopefully there will be more insights into why this happened and what the root cause was.

UPDATE:

Github.com, SquareSpace.com, Fastly.com all appear to be back online.

UPDATE:

I’m still having some difficulties getting information down from Github. A similar issue is occurring with ParrotSec’s mirrors so this may be unrelated to the CDN failure.