Unix Web Application Architectures. Unix Web Application Architectures. Samuli K. Other Places to Store the Session ID in. Expiring the Sessions. Explicit Session State is Good. Session State Mechanism Should be Flexible. Access Control and Authentication. HTTP Authentication. Implementing Authentication Yourself. Using a SQL Database as a Backend. Transactions and Error Recovery. Locking Between Simultaneous Requests. SQL as a Method of Communication. Reports. Request Parameter Validation. World Wide Web Server Software. Note: Some of this information may be out of date. A World Wide Web server, like the ftp daemon, is a program which responds to an incoming tcp connection and provides a service to the caller. Free support for linux, unix, unix commands, linux commands, linux server, linux ubuntu, shell scripts. Discuss Web Programming and Web Server Administration, including LAMP, Apache, MySQL, HTML. Unix Web Application Architectures. One might call a hit counter a web application, but a program so simple is not of much interest from an architectural point of view. Web server returns the response to Squid. Windows Web Servers vs. Unix/Linux Web Servers. Algorithm and Program For Area of. This includes making the standard freely available on the web, permitting reuse of the standard documentation in open source. Create a Web Server with XAMPP Lite's Apache HTTP Server. New webmasters coding primarily in HTML should choose a UNIX-based website hosting plan. Minimize the Number of Function Parameters. Separating Code and Output. HTML Templates. An Example. Advantages. Locking Data Between Requests. Security. Robustness Against Programmer Errors. An Alternate Approach: Abstracted HTMLIn this document I discuss various aspects of writing web. Unix. By a web application I mean a piece of software. Java or. other major extensions. The reader is expected to have a basic. HTML. Java. Script, HTTP and CGI. The focus is on problems that emerge when the. Issues related to building web sites in general. HTML pages, aren't considered. Rather, this can be seen as an essay about. I have learned when writing custom web applications for fun. Because I use Linux as my platform, only the. Linux are considered. However, everything. Unix variants. I mention. Apache a lot of times throughout the text as an example of a HTTP. This is simply because I use it, many others use it, and it's a. All feedback is very welcome. To give a picture. There are three user classes: admins, normal users and customers. Therefore it makes sense to try. When someone. codes a framework that does these things, and makes a product of it. The term used in this document shall be . Often done by a separate web server. Can be implemented by HTTP authentication, but other approaches can be better. However, it's not necessary to start building things. CGI. In this chapter I will. Some have high end features like. Many come with easily reusable component library. Usually. these also address non- coding related issues such as web site. HTML. writers. Most have a price tag of at least $1. But why bother since products like this already exist? Learning curve is another one: these are full development. If you already know well a programming. Perl, Python or Java, this. Flexibility may be another important factor: having. Then again, many are not. In any case, these products are not. In this. approach, the code is put into the HTML files. Before the web server sends. It's typically easy to start programming in these languages. They come with a comprehensive. I found PHP easy to learn. C++, Perl and shell), and. If not, the PHP web site gives more information. PHP. offers some kind of a solution to most points mentioned in section 2. Some features are implemented in a way that is in my opinion not. Therefore. the memory consumption can become quite high with a large number of. This is discussed in more detail in chapter. Memory Consumption. This way the perl bytecode is cached in the. Apache processes, which speeds up execution a lot. There exists a very large number of third. These things make it a good. PHP is probably easier to learn for those not. There was just the GET method with no additional. Not much was. won by using a separate web server, instead of embedding one as part of. But this was the situation 5 years ago. It includes 6 different methods, and 1. A good implementation should also work around bugs in. For example, some browsers don't work properly with. User- Agent field). For these reasons, if good. HTTP protocol compliance matters, it's a good idea to use a separate HTTP. An additional benefit of doing that is that often a part of the. HTTP access control or redirections. This might be a serious. That is, clients won't be normal browsers. It probably sounds. In some extreme cases. When. serving static files, the performance tends to be always sufficient. In. a quick test I performed, an Apache 1. Linux 2. 0. 3. 8 on a Pentium. II 3. 00 MHz, with quite default configuration, served over 3. If each of those small files mentioned. This is about two T1's. When serving 2. 5 kilobytes. T3. Even then. only a third of the CPU was used. I personally follow a rule of thumb that request. This kind of. delay will get lost in other delays in fetching a page and rendering it. For more rarely used operations the latency can of course. In 2. 00 ms you can do a lot with current CPU's. The compilation to bytecode. For example the. the command . Connections should. Starting the CGI program can be slow, especially if it's. Fundamentally, the benefit of having an always running. DB connection, precompiled HTML. In the Fast. CGI model, the CGI program is a. TCP/IP or. other mechanism once for each HTTP request. Fast. CGI defines how the CGI. CGI daemon over this connection, and how the reply is passed back. This also makes it possible to have the daemon. When a new request arrives, one of idle processes is. If there are no idle processes, more may be. This technique is called preforking. For example Apache works. Fast. CGI is. implemented as a CGI program written in C, because a computer such as. If you think latency significantly. This means that once you have generated a. This. is especially useful if the data from which the dynamic pages are. For instance, an application might cache the complex but rarely. When serving. a request, the pieces are merged and sent to the browser. This idea can. be generalized into any sub- results, such as commonly occurring database. Trying to add in caching once. Nothing is. easier than getting the cache and real data out of sync with each other. A lot has been written about this subject. Try for. Google search. Sometimes custom data storage code is necessary, but more. Using a. database doesn't automatically make things fast, sometimes almost the. Be familiar with your database, and do benchmarks. This can be an easy although not free way to. Usually. there are not many simultaneous requests underway, so latency matters. Of course, adding CPU's only helps if the application is able to. Remember though. that it may not be possible to distribute the database, which can thus. If. most of data isn't in buffers, things will slow down a great deal. This. of course applies to any kind of application. If no amount of RAM is. Not even in very high traffic sites. This should be. proof enough that performance isn't something you should excessively worry. Just don't make really stupid things, most. I listed above, and you should be okay for most. Assume processing a. CPU time, but 5 seconds of wall. If a site. gets 1. CPU time. Apache is an example of such server design. Apache 2. 0 is supposed to be able to run in a multithreaded. Especially the latter approach can lead into very small. The idea is that the. This way the process generating the. HTTP server accelerating means that you have Squid sitting. Squid. receives the HTTP request, and if the request is for a static or otherwise. Otherwise, Squid forwards the. Web server returns the response to Squid. Dynamic page serving speed isn't significantly degraded. In the example application, a. In our example application. Orders the customer has already placed, but not yet confirmed. The. user might want to still cancel or modify these orders. For. example assume some page shows a list of old orders by the user, and the. If. the user goes view other pages, and later comes back to the list, it should. For example a reference to the username of the. Each HTTP. request has no relation with any other HTTP request (aside from possibly. TCP connection). Therefore it's the job of the application to. In traditional GUI programming, each screen element. GUI toolkit object that holds all the data and state of the screen. In web applications, this data must be kept somewhere else. Included in that state. URLs for which that state is valid. The state object is called a cookie, for no. If session state is. Set- Cookie: HTTP response header. This. straightforward scheme has a number of problems that are discussed next. Even the size of. This may exceed the. RFC, or set by the browser. More likely, it will slow things down to have a lot of. HTTP request. Especially without SSL, it can also be seen to improve security. A new row. (record) is created into table Sessions to represent the new session. Let's say ID 4. 38. Other fields of the record contain the session. Note however that most of time people don't bother explicitly. From now on. I'll assume this kind of a system is used. This benefit is unique to cookies, and can't be achieved. They may have cookies disabled in their browser, or refuse to use. If a user has multiple browser. This effectively prevents a. One. mechanism, mentioned on Slashdot, keeps. ID in DNS name that the browser uses for referring the server. I have. not tried to use this method, so the details may be a little off, but here. If your application is on domain foo. DNS entry. *. foo. IP. When creating a new session with. ID, say, 9. 87. 65. Due. to the DNS wild card, this maps to the web server IP. The server application. ID that way. On the other. The server may. issue such redirection too, as Apache does for instance when one refers. This also binds the application. DNS of the domain, which complicates installation, and. I can imagine that in. DNS setup for sake of a single application. I also feel cautious. DNS and web caching mechanisms. DNS names referred in process of. For example, if the session ID is 9. HTTP method is. GET, the request for . If this can be semi- automated, it's quite doable. All the links and ACTION attributes of FORM elements must be. ID field into them, and that's. Of course the session will be lost if the user leaves the site and. URL's manually. The. Using this method, a request might be . The CGI program will. ID by looking at CGI PATH. If the application then only uses relative URL's for referring. ID stays automatically in the URL. For example. if the view given above has a link . For instance if a view. This means a link to a view must be. Therefore it may be best to not use hierarchical view names when. ID. It also requires. World Wide Web server software. Note. Some of this information may be out of date. A World Wide Web server, like the ftp. Includes the. complete source code. Platforms: unix. CERN server. The World Wide Web daemon program, full featured, with access. This daemon is also used as a basis. Platforms: unix, VMS. NCSA server. A server for files, written in C, public domain. Many features as. CERN's httpd. Platforms: unix. Spinner. Spinner is a modularised, object oriented World Wide Web HTTP/1. HTTP/0. 9 compliant server, distributed under the GPL license. Alibaba. A server for Windows NT provided by Computer Software Manufaktur. CL- HTTPCL- HTTP is a full- featured, object- oriented HTTP server written in Common. Lisp by John. Mallery at the M. I. T. It runs on MAC, UNIX, and the. Lisp Machine, and ports are underway to the PC. Go. Serve. A server for OS/2 supporting both HTTP and Gopher, from Mike. Cowlishaw of IBM UK Laboratories. GNA single server providing both HTTP and Gopher access to the same. In C, General Public License. Designed to help servers transition. WWW. Platforms: unix. GWHIS. Server. Specialized WWW Servers. Commercial, from Quadralay, Inc. HTTPS for Windows/NTService for NT. Configurable using control panel. Jungle. Server in Tk/TCL being written by Lindsay Marshall. Mac. HTTPServer for the Macintosh. Netsite. Commercially supported server from Netscape Communications Inc. Perl. serverfrom Marc Van. Heyningen at Indiana University. Written in. perl. Written by Peter Eriksson. Signum Support AB. Platforms. unix. Purveyor. Process Software's server for Windows NT and future Win. Windows 9. 5. REXX for VMA server consisting of a amall C program which passes control to a. REXX. HTTP for. VMBy R. M. Troth. Fields. A server which allows a world of data to be seen as part of the. World Wide Web universe is known as a gateway. For short tutorials with examples, see. It is a good idea to pick the basic daemon or one of the servers in the list as a starting point when making a. See. Last updated 1. January 2. 00. 2.
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