Why are Facebook and Google never down for maintenance?

1. Why are Facebook and Google never down for maintenance? #1 Scenario: You uploaded a file ‘ABC’ on the server, and now for the maintenance, you have to unplug the server. So, this will shut down the services connected with the server, and when the user requests the file, an error will appear until and unless it gets live again after maintenance. #2 Scenario: You uploaded a file ‘ABC’ on the server, and now the server is down for maintenance. To keep the services running, you can install another server. However, for this, you need to maintain redundant data- duplicated and synced regularly on both the servers so that they can operate together or simultaneously with a load balancer. When the user requests the file, the request goes to the router, which re-routes it to the new data destination that is towards the new server. Old requests which are already connected to the 1st server is maintained further taking no requests while the new traffic is diverted to the active server. What’s the mystery with Google & Facebook servers? With billions of daily active users, the tech giants Google (Video) and Facebook (Video) has built an extensive infrastructure to support this already massive and still growing user base. They have housed tens of thousands of computer servers, which are networked together in numerous gigantic data centers spread across the globe. Every time you make a request to Facebook or Google, the servers in these data centers receive the requests and distribute it across its network through fiber optics cables. Since the load is distributed among many servers and throughout the data centers, so the downtime is not visible to the end-user. But since the servers are machines, these require maintenance. However, the data is redundant and may be lying on a different server or maybe at some other data center location, so it is secured during the maintenance works or preserved even in disastrous situations and is available to the user whenever requested. A look at numbers: Facebook Datacenters: It has built 4 huge data centers with two more sites under construction as of September 2016, and leases additional server space from data center providers in several locations in and outside of the US. Facebook has not stopped building new data centers and is continuously seeking sites for new data centers. Google Datacenters: There are many data centers operated by Google across the world. At least 12 significant Google data center installations in the United States itself, with another 3 under construction. In Europe, Google is known to have equipment in at least 5 locations.