“What It Takes to Run Stack Overflow”, Nick Craver2013-11-22 (computer hardware; backlinks; similar)⁠:

I like to think of Stack Overflow as running with scale but not at scale. By that I meant we run very efficiently, but I still don’t think of us as “big”, not yet…We like to call it magic, other people call it “multiple servers with multi-core processors”—but we’ll stick with magic. Here’s what runs the Stack Exchange network in that data center:

• 4 MS SQL Servers

• 11 IIS Web Servers

• 2 Redis Servers

• 3 Tag Engine servers (anything searching by tag hits this, eg. /question/tagged/c++)

• 3 Elasticsearch servers

• 2 Load balancers (HAProxy)

• 2 Networks (each a Nexus 5596 + Fabric Extenders)

• 2 Cisco 5525-X ASAs (think Firewall)

• 2 Cisco 3945 Routers

…Performance is a feature, a very important feature to us. The main page loaded on all of our sites is the question page, affectionately known as Question/Show (its route name) internally. On November 12^th, that page rendered in an average of 28 milliseconds. While we strive to maintain 50ms, we really try and shave every possible millisecond off your pageload experience. All of our developers are certifiably anal curmudgeons when it comes to performance, so that helps keep times low as well. Here are the other top hit pages on SO, average render time on the same 24 hour period as above:

• Question/Show: 28 ms (29.7 million hits)

• User Profiles: 39 ms (1.7 million hits)

• Question List: 78 ms (1.1 million hits)

• Home page: 65 ms

…It’s definitely worth noting that these servers run at very low usage. Those web servers average between 5–15% CPU, 15.5 GB of RAM used and 20–40 Mb/s network traffic. The SQL servers average around 5–10% CPU, 365 GB of RAM used, and 100–200 Mb/s of network traffic.

…The primary reason the usage is so low is efficient code…Now that we know how Stack Overflow performs on its current hardware, next time we can see why we don’t run in the cloud.

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