A server is a computer, or a piece of software running on one, that listens for requests from clients over a network and sends back a response. The word covers both the physical machine and the program, such as a web server process.
Why it matters
Every website, API and email system depends on at least one server being reachable. When people say a site is down, the usual cause is that the server stopped answering, ran out of resources, or became unreachable from the network. Knowing which layer failed (hardware, operating system, or application) decides how you fix it.
Example
A browser asks GET / from a web server at 203.0.113.10 on port 443. The server software, such as nginx, reads the request, builds the page, and replies with an HTTP status 200 and the HTML. If nginx crashes, the machine can still be powered on and pingable while the website is down.
Common mistakes
- Treating a successful ping as proof the site works. Ping tests the network path, not the web application.
- Running the web server, database and mail on one machine with no monitoring, so one failure takes everything down.
- Confusing the hardware with the software role; a restart of the program is much faster than a reboot of the machine.
Related
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This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.