Why is XXX website down?

Incident reportedly occur around UTC 9:18PM 7/17/2020;

Cloudflare – an American web-infrastructure and website-security company most famously known for it’s Content delivery network (CDN) went down in certain region, taking out all websites that use its service.

cloudflare status update
cloudflare status update

While the origin is unknown, it has put up status update on its website as investigation and all sites seemly back up and running at the time of this writing.

What is CDN?

Content delivery network is essentially group of servers geographically distributed around the world to provide faster access to content of websites by caching them.

To use the service, websites let its DNS (Domain Name Server) managed by the provider. A DNS is basically a phone book, except it translates the domain of the site you’re accessing to an actual IP that hosts the site.

content delivery network
content delivery network

So instead of the server delivering content to potentially far away user, a regional server that hosts cache does the delivery instead. This greatly reduces latency, bandwidth cost, increase content availability even if origin server is down, and added benefit of mitigating DDoS (distributed denial-of-service attack).

I won’t be going into details of above list. In short, what happen is if the website you try to access uses cloudflare service, the DNS will come back with one of it’s regional server IP (instead of IP of the server that actually runs the website); But because the delivery server is down, you ended up not loading the website.

Due to popularity of its service, a lot of websites nowadays use Cloudflare CDN. And this kind of instance has happened before. So next time when you can’t access most of internet and there ain’t alien invading or huge solar flare knocking out all electronic, you know what’s up :)

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