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Web server

A web server is computer software and underlying hardware that accepts requests via HTTP (the network protocol created to distribute web content) or its secure variant HTTPS. A user agent, commonly a web browser or web crawler, initiates communication by making a request for a web page or other resource using HTTP, and the server responds with the content of that resource or an error message. A web server can also accept and store resources sent from the user agent if configured to do so.[1][2]

The hardware used to run a web server can vary according to the volume of requests that it needs to handle. At the low end of the range are embedded systems, such as a router that runs a small web server as its configuration interface. A high-traffic Internet website might handle requests with hundreds of servers that run on racks of high-speed computers.


A resource sent from a web server can be a pre-existing file (static content) available to the web server, or it can be generated at the time of the request (dynamic content) by another program that communicates with the server software. The former usually can be served faster and can be more easily cached for repeated requests, while the latter supports a broader range of applications.


Technologies such as REST and SOAP, which use HTTP as a basis for general computer-to-computer communication, as well as support for WebDAV extensions, have extended the application of web servers well beyond their original purpose of serving human-readable pages.

a graphical , called WorldWideWeb;

web browser

a portable ;

line mode web browser

a web server, later known as .

CERN httpd

implemented;

common features

performed;

common tasks

and scalability level aimed as a goal;

performances

model and techniques adopted to achieve wished performance and scalability level;

software

target hardware and category of usage, e.g. embedded system, low-medium traffic web server, high traffic web server.

Internet

number of requests per second (RPS, similar to , depending on HTTP version and configuration, type of HTTP requests and other operating conditions);

QPS

number of connections per second (CPS), is the number of connections per second accepted by web server (useful when using HTTP/1.0 or HTTP/1.1 with a very low limit of requests / responses per connection, i.e. 1 .. 20);

+ response time for each new client request; usually benchmark tool shows how many requests have been satisfied within a scale of time laps (e.g. within 1ms, 3ms, 5ms, 10ms, 20ms, 30ms, 40ms) and / or the shortest, the average and the longest response time;

network latency

of responses, in bytes per second.

throughput

Excess legitimate web traffic. Thousands or even millions of clients connecting to the website in a short amount of time, e.g., .

Slashdot effect

attacks. A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a computer or network resource unavailable to its intended users.

Distributed Denial of Service

that sometimes cause abnormal traffic because of millions of infected computers (not coordinated among them).

Computer worms

can cause high traffic because of millions of infected browsers or web servers.

XSS worms

Traffic not filtered/limited on large websites with very few network resources (e.g. bandwidth) and/or hardware resources (CPUs, RAM, disks).

Internet bots

(network) slowdowns (e.g. due to packet losses) so that client requests are served more slowly and the number of connections increases so much that server limits are reached.

Internet

Web servers, serving dynamic content, waiting for slow responses coming from computer(s) (e.g. databases), maybe because of too many queries mixed with too many inserts or updates of DB data; in these cases web servers have to wait for back-end data responses before replying to HTTP clients but during these waits too many new client connections / requests arrive and so they become overloaded.

back-end

Web servers () partial unavailability. This can happen because of required or urgent maintenance or upgrade, hardware or software failures such as back-end (e.g. database) failures; in these cases the remaining web servers may get too much traffic and become overloaded.

computers

Server (computing)

Application server

Comparison of web server software

(core part of a web server program that serves HTTP requests)

HTTP server

HTTP compression

Web application

Open source web application

List of AMP packages

Variant object

Virtual hosting

Web hosting service

Web container

Web proxy

Web service

Standard Web Server Gateway Interfaces used for dynamic contents:


A few other Web Server Interfaces (server or programming language specific) used for dynamic contents:

Mozilla: what is a web server?

Netcraft: news about web server survey