Several major websites around the internet went down out of the blue on June 8. A lot of popular websites like Reddit, Twitch, Forbes, BBC News, Quora, Vimeo, CNN and even Amazon were affected by the outage.
There was one thing in common among all of them, they all displayed 'Error: 503'.
What is Error 503?
To understand Error 503, let's take a look at how a website operates. On its own, a website is just a collection of codes and pages. These codes help dictate the formatting and layout of a page and what content is displayed on the layout.
The real workhorse is the webserver. Think of it as another computer but one that is specifically set up to handle requests to display a certain page. When you use the browser to navigate to a page, the webserver handles that request and pulls the information from its database and displays the relevant web page. Error 503 is what happens when a web server can't handle that request.
It doesn't mean that the webserver is faulty or malfunctioning, it just means that it is overloaded with so many requests that it cannot complete all of them.
Why does this happen?
There can be several reasons. One is a faulty firewall configuration on the server-side that is blocking requests. Another could be faulty hardware, one more could be a bug in a website's code that stops it from displaying properly. The error will also be shown in case there is too much web traffic, meaning more users are trying to log in to a website than what is supported.
Large-scale websites usually have a server farm which is a network of connected web servers that handle requests. If some of them go down, it puts a strain on the remaining servers, which reduces the number of active connections possible on a website drastically.
What happened in this case?
As per several media reports, the cause of the outage was traced to the content delivery network (CDN) provider Fastly.
According to a tweet put out by the company, the issue was caused by a faulty service configuration. Think of it as a set of rules that govern the distribution of content across websites. The problem here seemed to be caused by one of those rules breaking or a faulty rule.
Fastly is a CDN that hosts servers for several popular websites, so it makes sense that an error there caused a widespread outage. This issue has since been investigated and fixed.
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