Web server

HTTP, the network protocol designed to deliver web pages, or its secure version HTTPS, is used by a web server, which is composed of computer software and underlying hardware that accepts requests. A user agent, which is often a web browser or web crawler, starts communication by sending an HTTP request for a particular resource, and the server replies with the content of that resource or an error message, depending on the situation. It is also possible for the server to receive and keep resources supplied by the user agent, provided the server is configured to do so.

In theory, a server could be a single computer or even an embedded system, like a router with a built-in configuration interface. However, for websites with high traffic, web servers are typically deployed across a network of computers that are designed to handle large numbers of requests for documents, multimedia files, and interactive scripts. Depending on the web server, a resource delivered from the server may be a preexisting file that is already accessible to the server, or it can be a file that is created at the moment of the request by another programme that interacts with the web server programme. In many cases, the former is quicker and more readily stored for repeated queries, while the latter offers a wider variety of application scenarios. When it is feasible, websites that offer produced content will integrate saved files into their design.

Using HTTP as the foundation for universal computer-to-computer communication, technologies such as REST and SOAP have broadened the scope of web servers' use well beyond their initial goal of delivering human-readable pages.