StackOverflow: 560 million hits per month, 25 servers

StackOverflow has published attendance statistics for all StackExchange sites. At the moment, StackExchange ranks 54th in the Internet by audience. The site has 4 million registered users, 8 million questions and 40 million answers have been published. Attendance is 560 million views per month.

Surprisingly, only 25 servers are enough for StackOverflow to work. But since the CPU load is about 10-15%, then all the work could be performed by 5 servers.

Statistics

• Annual attendance growth of 100%
• 2 TB of SQL data on SSDs
• Each server has two 320 GB SSDs in RAID 1
• 40:60 read-write ratio
• On database servers, the average CPU load is 10%
• 11 web servers on IIS
• 2 servers for load balancers (load balancers), 1 active, installed HAProxy
• 4 active database nodes, installed MS SQL
• 3 application servers with tag search engine
• 3 servers with ElasticSearch search engine
• 2 machines with distributed cache under Redis
• 2 network hubs (Nexus 5596 + Fabric Extenders)
• 2 Cisco 5525-X ASA Firewalls
• 2 Cisco 3945 routers
• 2 read-only SQL servers for use with the Stack Exchange API
• Virtual machines for various functions

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