Memcached is a well known, simple, inmemory caching solution. This paper describes how Facebook leverages memcached as a building block to
construct and scale a distributed keyvalue store that
supports the world’s largest social network. Our system
handles billions of requests per second and holds trillions of items to deliver a rich experience for over a billion users around the world.

Resources
https://www.usenix.org/system/files/c...
https://en.wikipedia.org/wiki/Consist...
https://www.nginx.com/resources/gloss...
https://memcached.org/