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560 MILLION pages views per month

It’s all about performance
That means we transfer 34 TB data / month

9 web servers

RAM: 48GB

4 sql servers

Organized as 2 clusters

Stack Overflow

RAM: 384 GB • DB size: 1.6 TB

Stack Exchange, Careers, Meta

RAM: 288 GB • DB size: 1.2 TB

2 redis servers

RAM: 96GB
redis
Master
redis
Slave
It’s a unique custom, high performance index of Stack Exchange questions.
server server server

3 tag engine servers

RAM: 32GB

3 elasticsearch servers

RAM: 196GB • Load balanced
server server server

2 Haproxy servers

HAProxy Server
1 live
HAProxy Server
1 fail over
Websockets

Web Sockets

Programming

Stack

All of these make the pages render in

52ms
home page
33ms
questions page