The Shots APP we use the following technology to serve many millions of Photos, Videos and Cached Links.
RedHat Enterprise 6 on the Front ends and DBs. Amazon Linux (Centos) on Elastic Search and Go servers
Percona 5.6 XTRADB with some minor custom stuff (sharded)
we have a little bit of Python, JAVA and a lot of GO!
One of the current features which has wildly been successful is sharing links on mobile, which is very hard. Mobile is not built for links but fortunately Instagram and YouTube are. To make this work; we have the client read from the clipboard. The client makes a call home where the link is sent to a distributed worker system which fetches the content of the HTML page, finds the media, manipulates the media and then distributes the media on our CDN. Links only last for a few days.
This is like a poor man's AMP and only took us a few days to write. We even retranscode videos to make sure the format fits our timeline and doesn't hog up to much bandwidth.
MySQL keeps state so the same link is not rebuilt and everything is fronted with Redis - since redis supports pipelined commands - which is great for a feed our size. The next feed version will be a go-tao-like system.
All in all for 3 days of work, the system works great and scales linearly. It is near real time. Give it a try. Link a Instagram or Youtube url and you will see for yourself.
Some things that I'd like to do in the future is use QUIC on a websocket layer. To have a non-blocking messaging system which is blazing fast and works on spotty networks and integrate ROCKSDB.
But that's another post.