I noticed that GitHub was down this morning — or not down, exactly, but its web pages were profoundly broken. I tried different browsers, then jumped on Twitter to see if it was widely reported.
It was. People were saying the problem was Fastly, a content delivery network (CDN). Also that it was affecting other sites. I don’t know when CDNs started being a thing. I think they might have been recommended by some when I was still using WordPress. The idea being that a CDN can host your site’s static assets — images, mainly — while WordPress carries on with the dynamic bits, generating HTML pages on the fly, as it does. The CDN’s scale will mean it can serve those files faster than your little server.
I didn’t bother with them, not having that much traffic. But in the back of my mind there was always the thought, ‘What if the CDN goes down?’ The idea, of course, was that the CDN would be big, multiply-redundant, reliable: it’s not going to go down!
Here’s a CNN report about the outage. It affected a lot more than GitHub, it seems.
So, are CDNs single points of failure? Obviously there’s more than one CDN, but if the failure of any one can disable large chunks of the web, do they put us in a better position?