{"id":221,"date":"2017-09-06T20:49:20","date_gmt":"2017-09-06T20:49:20","guid":{"rendered":"http:\/\/www.volucer.it\/?p=221"},"modified":"2017-09-06T20:49:20","modified_gmt":"2017-09-06T20:49:20","slug":"web-server-architecture","status":"publish","type":"post","link":"https:\/\/www.volucer.it\/?p=221","title":{"rendered":"WEB SERVER ARCHITECTURE"},"content":{"rendered":"

Web servers, browsers, and proxies communicate by exchanging HTTP messages on a network structure using the request-response virtual circuit.<\/span><\/p>\n

Web severs enable HTTP access to a collection of documents. And other information organized into a tree structure, much like a computer file system.<\/span><\/p>\n

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Figure 1 - Request-Response Schema<\/figcaption><\/figure>\n

Web server receives and interprets HTTP requests from a client generally a browser. Then it examines the requests and maps the resource identifier to a file or forwards the request to a program which then produces the requested data. Finally, the server sends the response back to the client. <\/span><\/p>\n

The behaviour of a single-tasking HTTP Server using the Petri Net<\/span><\/span>1<\/a><\/span><\/sup> formalism is shown in Fig. 2.<\/span><\/span><\/p>\n

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1<\/a> A Petri net consists of <\/span><\/span>places<\/i><\/span><\/span>, <\/span><\/span>transitions<\/i><\/span><\/span>, and <\/span><\/span>directed arcs<\/i><\/span><\/span>. Arcs run from a place to a transition or vice versa, never between places or between transitions. The places from which an arc runs to a transition are called the <\/span><\/span>input places<\/i><\/span><\/span> of the transition; the places to which arcs run from a transition are called the <\/span><\/span>output places<\/i><\/span><\/span> of the transition. More information is at link <\/span><\/span>http:\/\/en.wikipedia.org\/wiki\/Petri_net<\/span><\/span><\/a><\/u><\/span>. <\/span><\/span><\/p>\n<\/div>\n

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Figure 2 \u2013 Behavior of a single-tasking HTTP server.<\/figcaption><\/figure>\n

WEB SERVER REFERENCE ARCHITECTURE<\/h3>\n

In this section we are going to show the reference architecture for web server domain. It defines the fundamental components of the domain and the relations between these components.<\/span><\/p>\n

The reference architecture provides a common nomenclature across all software systems in the same domain, which allows: <\/span><\/p>\n

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  1. \n

    to describe uniformly the architecture of a web server and to understand a particular web server passing before through its conceptual architecture and then through its concrete architecture, which may have extra features based on its design goals. For example, not all web servers can serve Java Servlets;<\/span><\/p>\n<\/li>\n

  2. \n

    to compare different architecture by using a common level of abstraction.<\/span><\/p>\n<\/li>\n<\/ol>\n

    The web server reference architecture proposed is shown in Fig. 3. As you can see, it specifies the data flow and the dependencies between the seven subsystems. These major subsystems are divided between two layers: a <\/span><\/span>server layer<\/i><\/span><\/span> and a <\/span><\/span>support layer<\/i><\/span><\/span>.<\/span><\/span><\/p>\n

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    Figure 3 - Web Server reference architecture.<\/figcaption><\/figure>\n

    The Server Layer contains five subsystems that encapsulate the operating system and provides the requested resources to the browser using the functionality of the local operating system. We will now describe every subsystem of the layer.<\/span><\/p>\n