  Apache Overview HOWTO
  Daniel Lopez Ridruejo, ridruejo@apache.org
  v0.6, 8 March 2001

  This documents gives you an overview of the Apache webserver and
  related projects. It provides pointers for further information and
  implementation details.
  ______________________________________________________________________

  Table of Contents



  1. Introduction

  2. Apache

  3. Apache Software Foundation

  4. Developing web applications with Apache

     4.1 Static
     4.2 Dynamic content
     4.3 CGI scripts
     4.4 Site generators
     4.5 Out of process servers
     4.6 Fast CGI
     4.7 Java servlets
     4.8 Embeded interpreters

  5. Performance and bandwidth management

  6. Virtual hosting

  7. Load balancing

  8. Secure transactions

  9. SNMP

  10. Authentication modules

  11. GUIs for Apache

  12. Writing Apache modules

  13. Apache books

  14. WebDAV

  15. Java projects

     15.1 Ant
     15.2 ORO and Regexp
     15.3 Slide
     15.4 Struts
     15.5 Taglibs
     15.6 Tomcat
     15.7 Velocity
     15.8 Watchdog
     15.9 JServ
     15.10 JSSI
     15.11 Apache JMeter
     15.12 Server Pages Foundation Classes
     15.13 Element Construction Set
     15.14 Avalon
     15.15 JAMES (Java Apache Mail Enterprise Server)
     15.16 PicoServer
     15.17 Jetspeed
     15.18 Turbine
     15.19 Jyve
     15.20 Alexandria
     15.21 Log4j

  16. XML projects

     16.1 Introduction to XML
     16.2 Xerces
     16.3 Xalan
     16.4 FOP
     16.5 Cocoon
     16.6 Xang
     16.7 SOAP
     16.8 Batik
     16.9 Crimson
     16.10 Other XML projects

  17. Perl

     17.1 Embperl
     17.2 Mason
     17.3 Mod_Perl

  18. PHP

  19. Python

  20. Tcl

  21. Modules for other languages

  22. Apache 2.0

  23. Migrating from Netscape (iPlanet) web servers

  24. Migrating from Microsoft IIS

  25. Links

     25.1 Websites
     25.2 Java application servers

  26. Contacting the author

     26.1 Translations


  ______________________________________________________________________

  1.  Introduction

  This document gives you an overview of the Apache web server and
  related projects.  Apache is the most popular server on the Internet
  <http://www.netcraft.com/survey/>. New Apache users, specially those
  coming from a Windows background, are often unaware of the
  possibilities of Apache, useful addons and, more in general, how
  everything works together. This document aims to show a general
  picture of such possibilities with a brief description of each one and
  pointers for further information.  The information has been gathered
  from many sources, including projects' web pages, conference talks,
  mailing lists, Apache websites and my own hands-on experience. Full
  credit is given to these authors. Without them and their work this
  document would not have been possible or necessary.

  Disclaimer: I work for Covalent <http://www.covalent.net>. We provide
  products and support services for the Apache webserver, and I mention
  some of them here, as I do for our competitors and similar open source
  projects.

  If you find typos, errors or you have suggestions for improvement or
  comments, please let me know so I can correct the document.



  2.  Apache

  Apache is the leading internet web server, with over 60% market share,
  according to the Netcraft survey <http://www.netcraft.com/survey>.
  Several key factors have contributed to Apache's success:

  ·  The Apache license <http://www.apache.org/LICENSE.txt>. It is an
     open source, BSD-like license that allows for both commercial and
     non-commercial uses of Apache.

  ·  Talented community of developers
     <http://www.apache.org/contributors/index.html> with a variety of
     backgrounds and an open development process based on technical
     merits.

  ·  Modular architecture. Apache users can easily add functionality or
     taylor Apache to their specific enviroment.

  ·  Portable: Apache runs on nearly all flavors of Unix (and Linux),
     Windows, BeOs, mainframes...

  ·  Robustness and security

     Many commercial vendors have adopted Apache based solutions for
     their products, including Oracle <http://www.oracle.com>, Red Hat
     <http://www.redhat.com> and IBM <http://www.ibm.com>.  In addition,
     Covalent <http://www.covalent.net> provides add-on modules and 24x7
     support for Apache.

  The following websites use Apache or derivatives. Chances are that if
  Apache is good enough for them, it is also good enough for you :)

  ·  Amazon.com <http://www.amazon.com>

  ·  Yahoo! <http://www.yahoo.com>

  ·  W3 Consortium <http://www.w3c.org>

  ·  Financial Times <http://www.ft.com>

  ·  Network solutions <http://www.networksolutions.com>

  ·  MP3.com <http://www.mp3.com>

  ·  Stanford <http://www.stanford.edu>

  >From the Apache website <http://www.apache.org>:

  The Apache Project is a collaborative software development effort
  aimed at creating a robust, commercial-grade, featureful, and freely-
  available source code implementation of an HTTP (Web) server.

  The Apache project has grown beyond building just a web server into
  other critical server side technologies like Java or XML. The Apache
  Software Foundation, described in the next section serves as an
  umbrella for these projects.


  Related talk

  ·  W09: Introduction to the Apache Web Server

  ·  F16: Licensing issues in commercial OSS products



  3.  Apache Software Foundation

  The Apache Software Foundation exists to provide organizational,
  legal, and financial support for the Apache open-source software
  projects. Formerly known as the Apache Group, the Foundation has been
  incorporated as a membership-based, not-for-profit corporation in
  order to ensure that the Apache projects continue to exist beyond the
  participation of individual volunteers, to enable contributions of
  intellectual property and funds on a sound basis, and to provide a
  vehicle for limiting legal exposure while participating in open-source
  software projects.

  Or, as Roy T. Fielding, the chairman of the ASF describes it: The
  mission of the Apache Software Foundation is to facilitate and support
  collaborative software development projects that use the Apache
  methods of collaboration over the Internet to create, maintain, and
  extend the infrastructure of the Web and enforce the standards that
  define it.

  You can learn more about the foundation here
  <http://www.apache.org/foundation/>.


  4.  Developing web applications with Apache

  There are several ways of providing content with Apache.


  Related talk

  ·  W07: Web Application Technologies - surveying the landscape


  4.1.  Static

  Apache can serve static content, like HTML files, images, etc.  If
  this is all you need, Apache is probably right for you.  A low end
  Pentium running Linux and Apache can easily saturate a 10Mbps line
  serving static content. If that is your primary use of Apache, make
  sure you also check the ``performance'' section.

  4.2.  Dynamic content

  For many websites, the information changes constantly and pages need
  to be updated periodically or generated on the fly. This is what
  server side programming is all about: programming languages, tools and
  frameworks that help developers query and modify information from
  different sources (databases, directory services, customer records,
  other websites) and deliver the content to the user.

  4.3.  CGI scripts

  CGI stands for Common Cateway Interface. CGI scripts are external
  programs that are called when a user requests a certain page. The CGI
  receives information from the web server (forms variable values, type
  of browser, IP address of the client, etc) and uses that information
  to output a web page for the client.

  Pros: Since it is an external program, it can be coded any language
  and the same script will also be portable among different web servers.
  The CGI protocol is simple, and the return result consists of writing
  the response to the standard output. It is a mature technology, and
  there are plenty of online and book references and examples.

  Cons: Spawning and initializing a process takes time. Since a CGI is
  external to the server and an instance has to be launched/destroyed
  for every request there is a performance hit. If the process has to
  load external libraries or perform a connection to an external
  database the delay can be important. Same thing if the number of hits
  per second is high. CGIs are stateless and session management has to
  be achieved by external means.

  Since CGI usually involves heavy text manipulation, scripting
  languages are the natural choice. Part of Perl <http://www.perl.com/>
  popularity stems from being the CGI programming language of choice.
  This is due to its extensive support for string handling and text
  processing. There are plenty of freely available CGI scripts and
  libraries. A good starting point is: the Open Directory CGI section
  <http://dmoz.org/Computers/Programming/Internet/CGI/>

  4.4.  Site generators

  If your site is high volume, you may run into performance problems
  when generating content dynamically. Offline content generators are an
  alternative.  These solutions separate content from presentation. The
  HTML generator reads both sources and outputs the static files that
  build the website. The generator can be run periodically or triggered
  by content changes.

  Future versions of ``Cocoon'' plan on having a batch mode to
  accomplish this. Another option is the Web site meta language
  <http://www.engelschall.com/sw/wml/>.

  4.5.  Out of process servers

  The web server can pass dynamic requests to another program. This
  program sits idle until a request comes. The request is processed and
  returned to the webserver which in turn returns it to the client. This
  eliminates the overhead associated with CGI scripts. Examples of this
  approach are ``Fast CGI'', ``Java servlets'', etc.

  4.6.  Fast CGI

  This standard was developed to address some shortcomings of the CGI
  protocol. The main improvement is that a single spawned process can
  process more than one request. There is an Apache module that
  implements the Fast CGI protocol and libraries for Tcl, Perl etc. More
  information at


  Related talk

  ·  F18: FastCGI -- The forgotten treasure


  4.7.  Java servlets

  An external Java virtual machine processes requests. The JVM can
  reside in the same computer or in a different one. This is how a lot
  of application servers work. Usually standard libraries are included
  for server side processing. You want to check ``JServ'' and
  ``Tomcat''. Related Java application server projects can be found
  ``here''


  Related talk

  ·  W16: Recommendations for Java-Based Web Application Architectures



  4.8.  Embeded interpreters

  An alternative to out-of-process webservers is to embed the
  interpreter in the server itself. There are roughly two categories in
  this kind of modules: Modules that answer or modify requests directly
  and modules aimed to process commands embeded in HTML pages before
  serving it to the client. The most representative approaches are
  ``mod_perl'' and ``PHP''


  5.  Performance and bandwidth management

  Raw performance is only one of the factors to consider in a web server
  (flexibility and stability come usually first).

  Having said that, there are solutions to improve performance on heavy
  loaded webservers serving static content. If you are in the hosting
  business Apache also provides ways in which you can measure and
  control bandwidth usage.  Throttling in this context usually means
  slowing down the delivery of content based on the file requested, a
  specific client IP address, etc. This is done to prevent abuse.

  ·  mod_mmap: Included in current Apache releases, it maps to memory a
     statically configured list of frequently requested but not changed
     files.

  ·  Mod_bandwidth <http://www.cohprog.com/mod_bandwidth.html>: Enables
     the setting of server-wide or per connection bandwidth limits,
     based on the specific directory, size of files and remote
     IP/domain.

  ·  Bandwidth share module
     <http://www.topology.org/src/bwshare/README.html>: provides
     bandwidth throttling and balancing by client IP address. It is
     actively maintained.

  ·  Mod_throttle
     <http://www.snert.com/Software/Throttle/index.shtml>:Throttle
     bandwidth per virtual host or user.

  ·  Mod_throttle_access <http://www.fremen.org/apache/>: useful if you
     are slashdotted <http://everything2.com/index.pl?node_id=13464>.
     Allows throttling based on resources (file, directory, etc.)


  6.  Virtual hosting

  Apache provides extensive virtual hosting support, there are
  additional modules that provide specific functionality:


  ·  mod_dynvhost <http://funkcity.com/0101/>

  ·  mod_pweb <http://www.joytec.de/mod_pweb.html>

  ·  mod_v2h <http://www.fractal.net/mod_v2h.tm>

  In addition, Apache 2.0 allows children serving different domains to
  have different user ids, improving security.


  7.  Load balancing

  Apache has several modules that allow distribution of requests among
  servers, for redundancy, increased availability, etc.

  ·  Reverse proxying + mod_rewrite: There is nothing in Apache that you
     can not do with mod_rewrite
     <http://www.apache.org/docs/mod/mod_rewrite.html> ... :) This
     technique consists of having an Apache front-end server acting as a
     proxy for the backend servers. You can find more information here
     <http://www.apache.org/docs/misc/rewriteguide.html>

  ·  Mod_redundacy: Takeover web and ip in case of failure. You can find
     more information here <http://www.ask-the-guru.com>.

  ·  Mod_backhand: Allows seamless redirection of HTTP requests from one
     web server to another. This redirection can be used to target
     machines with under-utilized resources, thus providing fine-
     grained, per-request load balancing of web requests. More
     information at .


  Related talk

  ·  TH06: mod_backhand: Internals explained


  8.  Secure transactions

  There are several solutions that provide secure transactions for
  Apache servers.  This enables Apache servers to be used for ecommerce
  or other scenarios where sensitive information is exchanged (like
  credit card numbers).

  ·  Mod_ssl <http://www.modssl.org> and Apache-SSL <http://www.apache-
     ssl.org> are open source implementations. They are European based,
     unencumbered by RSA patents.

  ·  Red Hat <http://www.redhat.com> offers a secure server derived from
     Apache. Red Hat adquired C2Net, makers of StrongHold, another
     Secure server derived from Apache.

  ·  Covalent <http://www.covalent.net> sells secure versions of Apache
     as well as the CovalentSSL module that plugs on existing Apache
     installations.

  Credit card transactions

  Apache specific solutions exist for credit card transactions:

  ·  Cypay <http://www.cypay.com/> credit card module for Apache.
     Template based, tax calculations.

  ·  Covalent credator <http://www.covalent.net>, multiple
     clearinghouses support, failover operation, PHP, Perl, Java
     support.



  9.  SNMP

  SNMP stands for Simple Network Management Protocol. It allows
  monitoring and management of network servers, equipment, etc. SNMP
  modules for Apache help manage large deployments of web servers,
  measure the quality of service offered and integration of Apache in
  existing management frameworks.

  ·  Open source Mod SNMP
     <http://www.simpleweb.org/software/packages/mod-snmp/> for Apache
     1.3.
  ·  Covalent SNMP <http://www.covalent.net> provides a commercial SNMP
     module, support for the latest SNMPv3 standard, integration with
     HP-Openview, Tivoli, etc.



  10.  Authentication modules

  In many situations (subscription services, sensitive information,
  private areas), user authentication is required. Apache includes basic
  authentication support. Additional authentication modules exist that
  connect Apache to existing security frameworks or databases,
  including: NT Domain controller, Oracle, mySQL, PostgresSQL, etc.

  The LDAP modules are specially interesting, as they allow integration
  with company and enterprise wide existing directory services.

  You can find these modules at .



  11.  GUIs for Apache

  Apache is configured thru text configuration files. This has
  advantages and disadvantages. Management can be done from any computer
  that has internet access via ssh <http://www.openssh.com>. Editing a
  configuration file by hand implies a learning curve. There are open
  source graphical tools that make this task easier:

  ·  Comanche <http://www.comanche.org>: It is crossplatform and runs on
     Unix/Linux, Windows and Mac. Check the website for screenshots and
     in-depth information. Disclaimer: I am the main author of Comanche,
     so remember, there are no bugs, only undocumented features :)

  ·  gui.apache.org <http://gui.apache.org>: GUI interfaces for Apache
     project. Programs with various degrees of development.

  ·  Webmin <http://www.webmin.com/webmin/>: A nice web based interface.


  12.  Writing Apache modules

  Apache, like many other successful open source projects has a modular
  architecture.  This means that to add or modify functionality you do
  not need to know the whole code base.  Source code access for Apache
  means that you can custom build the server with only the modules that
  you need and include your owns.

  Extending Apache can be done in C or in a variety of other languages
  using appropriate modules.  These modules expose Apache's internal
  functionality to different programming languages like Perl or Tcl.

  Writing modules in C: Apache is written in C and so they are the
  modules distributed with Apache.  The best way to get started writing
  Apache modules is to read Doug MacEachern and Lincoln Stein Writing
  Apache modules with Perl and C <http://www.modperl.com>. It is a well-
  written, easy to read book by two Apache and Perl gurus. The above
  link will lead you to the book website, which has some of its chapters
  online.  If you have not the money to buy the book or cannot borrow it
  from a friend, there are other ways.  You can read some of the online
  tutorials on writing Apache modules: Ken Coar, an Apache Group member,
  has a nice tutorial and slides online
  <http://web.golux.com/coar/slides/>.  An overview of the Apache
  architecture can be found here
  <http://www.grad.math.uwaterloo.ca/~oadragoi/CS746G/a1/apache_conceptual_arch.html>.
  The Apache website has some API notes
  <http://www.apache.org/docs/misc/API.html> that can help you get
  started. You are also encouraged to browse the source code of the
  modules included with Apache. Apache includes a simple one
  (mod_example.c) for that purpose.

  Writing Apache modules in other languages: There is a variety of
  Apache modules that enable third party languages to access the
  internal Apache API.  The most popular is ``mod_perl''.

  If you have any questions about the development of an Apache module
  you should join the Apache modules mailing list at .  Remember to do
  your homework first, research past messages and check all the
  documentation previously described. Chances are somebody had the same
  problem that you are experiencing and he got an useful response.

  If you are interested in the development of core Apache itself, you
  should checkout the Apache development site <http://dev.apache.org>.



  13.  Apache books

  A comprehensive list of Apache books can be found athere
  <http://www.apache.org/info/apache_books.html>.

  A couple of books that I personally recommend are:

  ·  Writing Apache Modules with Perl and C <http://www.modperl.com> if
     you are interested in Apache internals.

  ·  Apache server for dummies <http://apache-server.com/> if you want
     to get started with Apache. Do not get fooled by the name. This is
     a comprehensive book packed with useful information.


  14.  WebDAV

  >From the WebDAV website <http://www.webdav.org>: WebDAV stands for
  "Web-based Distributed Authoring and Versioning". It is a set of
  extensions to the HTTP protocol which allows users to collaboratively
  edit and manage files on remote web servers.

  It is the open standards equivalent of the MS FrontPage protocol, but
  it takes the idea several steps further. It enables other protocols to
  be built on top of it (See the Subversion website
  <http://subversion.tigris.org/> for an example.



  15.  Java projects

  For historical reasons, Java projects can be found both under the
  java.apache.org and jakarta.apache.org umbrellas. The final goal is
  that over time all Java projects will move under the Jakarta umbrella.

  The goal of the Jakarta Project is to provide commercial-quality
  server solutions based on the Java Platform that are developed in an
  open and cooperative fashion.

  The Java on Apache community is a very dynamic and active one, as
  shows the quantity and quality of its subprojects, which are described
  now.


  15.1.  Ant

  You can think of Ant as the Java equivalent of make. It is a big
  success with Java related projects. Developers can write Java instead
  of shell commands. This means increased portability and extensibility.
  Instead of Makefiles Ant has XML files.  You can learn more about ANT
  here <http://jakarta.apache.org/ant/index.html>.


  Related talk

  ·  F19: Using Ant to build Java code


  15.2.  ORO and Regexp

  ORO is a complete package that provides regular experession support
  for Java. It includes Perl5 regular expression support, glob
  expressions, etc.  All under the Apache license.  You can learn more
  about ORO here <http://jakarta.apache.org/oro/index.html>. You can
  find another lightweight regular expression package, Regexp
  <http://jakarta.apache.org/regexp/>.

  15.3.  Slide

  Slide is a high-level content management framework.  Conceptually, it
  provides a hierarchical organization of binary content which can be
  stored into arbitrary, heterogenous, distributed data stores. In
  addition, Slide integrates security, locking and versioning services.

  If you are familiar with WedDAV <http://www.webdav.org>, Slide uses it
  extensively. In simple words, what Slides provides is an unified,
  simple way to access resources and information. These resources can be
  stored in a database, the filesystem, etc. and accessed either thru a
  WebDAV interface or Slide own API.

  You can learn more at the Slide home page
  <http://jakarta.apache.org/slide/index.html>.


  15.4.  Struts

  Struts is an Apache project that tries to bring the Model-View-
  Controller (MVC) design paradigm to web development. It builds on
  Servlet <http://java.sun.com/products/servlet> and JavaServer Pages
  <http://java.sun.com/products/jsp> technologies. The model part are
  the Java server objects, which represent the internal estate of the
  application.  Enterprise Java Beans are commonly used here. The view
  part is constructed via JavaServer Pages (JSP) which are a combination
  of static HTML/XML and Java. JSPs also allow the developer to define
  its own tags.  The controller part are servlets, which take requests
  (GET/POST) from the client, perform actions on the model and update
  the view by providing the appropriate JSP.  You can learn more at the
  Struts project pages <http://jakarta.apache.org/struts/index.html>.

  15.5.  Taglibs

  The JavaServer pages technology allows developers to provide
  functionality by adding custom tags. The Taglibs project intends to be
  a common repository for these extensions. It includes tags for common
  utilities (for, date), SQL database access, etc.

  You can learn about TagLibs here
  <http://jakarta.apache.org/taglibs/index.html>.  More documentation is
  included in the package.

  15.6.  Tomcat

  Tomcat is the flagship product of the Jakarta project.  It is the
  official reference implementation for the Java Servlet 2.2 and
  JavaServer Pages 1.1 technologies.

  You can learn more in the Tomcat homepage
  <http://jakarta.apache.org/tomcat/index.html>. The Tomcat project was
  started with a code donation from Sun Microsystems.



  15.7.  Velocity

  Velocity is a Java based template engine. It can be used as a stand-
  alone utility for generating source code, HTML, reports, or it can be
  combined with other systems to provide template services.  Velocity
  has a Model View Controller paradigm that enforces separation of Java
  code and the HTML template.

  You can learn more about Velocity here
  <http://jakarta.apache.org/velocity/index.html>. Velocity is part of
  other projects like ``Turbine''


  15.8.  Watchdog

  The Watchdog project provides the validation tests for the Servlet and
  JavaServer Pages specifications. You can find more information here
  <http://jakarta.apache.org/watchdog/index.html>


  15.9.  JServ

  Apache JServ is a 100% pure Java servlet engine fully compliant with
  the JavaSoft java Servlet APIs 2,0 specification.(...)The result is a
  pure servlet engine that works on any "version 1.1" Java Virtual
  Machine.

  JServ is one of the original Java Apache projects. ``Tomcat'' will be
  the successor of JServ once it is finished.  You can learn more at the
  JServ home page <http://java.apache.org/jserv/index.html>.


  15.10.  JSSI

  JSSI is an implementation of server side included in the Java
  language.  Server side includes are tags includes in files that get
  processed before the page is served to the client (for example to
  include the current date) You can find more information here
  <http://java.apache.org/jservssi/index.html>.

  15.11.  Apache JMeter

  The Apache JMeter is a 100% pure Java desktop application designed to
  load test functional behavior and measure performance. It was
  originally designed for testing Web Applications but has since
  expanded to other test functions.

  It can be used to test static and dynamic resources and get inmediate
  visual feedback.

  You can see some screenshots and learn more here
  <http://java.apache.org/jmeter/index.html>.

  15.12.  Server Pages Foundation Classes

  Is a set of libraries to help solve common problems in server side
  application development. They focus on two of them:

  ·  Mixing HTML and Java: Provides a library of classes that takes care
     of the HTML generation and that can be integrated with the rest of
     the Java code.

  ·  HTTP is a stateless protocol: SPFC provides session support, so
     applications can keep track of users as they navigate the website.
     The application developer does not need to worry about the specific
     details of page generation. He can think in more general
     traditional application terms.  You can learn more about SPFC here
     <http://java.apache.org/spfc/index.html>


  15.13.  Element Construction Set

  Element Construction Set (ECS) is a JAVA API or generating elements
  for various markup languages it directly supports HTML 4.0 and XML,
  but can easily be extended to create tags for any markup language.

  It allows the generation of mark up tags using Java function calls,
  leading to a much cleaner solution that mixing HTML and Java code.
  You can learn more at the ECS project page
  <http://java.apache.org/ecs/index.html>.

  15.14.  Avalon

  If you are familiar with Perl or BSD systems, Avalon is roughly the
  equivalent of CPAN <http://www.cpan.org> or the Ports collection for
  Java Apache technologies. It does not only provide guidelines for a
  common repository of code, it goes one step further: is an effort to
  create, design, develop and maintain a common framework for server
  applications written using the Java language. It provides the means so
  server side Java projects can be easily integrated and build on each
  other.

  15.15.  JAMES (Java Apache Mail Enterprise Server)

  Complementary to the other Apache server side technologies, JAMES
  provides a 100% pure Java server designed to be a complete and
  portable enterprise mail engine solution based on currently available
  open protocols (SMTP, POP3, IMAP, HTTP)

  More information can be found here
  <http://java.apache.org/james/index.html>.

  15.16.  PicoServer

  A lightweight HTTP/1.0 server in pure Java. The project seems to be
  stalled and no code is available. The website can be found here
  <http://java.apache.org/picoserver/index.html>.

  15.17.  Jetspeed

  Jetspeed <http://java.apache.org/jetspeed/site/overview.html> is a web
  based portal written in Java. It has a modular API that allows
  aggregation of different data sources (XML, SMTP, iCalendar)


  Related talk:

  ·  TH11: Writing an enterprise information portal with JetSpeed

  15.18.  Turbine

  Turbine is a servlet based framework that allows experienced Java
  developers to quickly build secure web applications. Turbine brings
  together a platform for running Java code and reusable components,
  everything under the Apache license. Some of it features

  ·  Integration with template systems

  ·  MVC style development

  ·  Access Control Lists

  ·  Localization support

  ·  etc.

     If you are interested, you can visit the Turbine web site
     <http://java.apache.org/turbine/features.html>.


  15.19.  Jyve

  The Jyve project <http://java.apache.org/jyve/index.html> is built on
  top of the Turbine framework. It is an application that provides a web
  based FAQ system

  15.20.  Alexandria

  Alexandria is an integrated documentation management system. It brings
  together technologies common to many open source projects like CVS and
  JavaDoc.  The goal is to integrate source code and documentation to
  encourage code documentation and sharing. More information here
  <http://java.apache.org/alexandria/index.html>


  Related talk

  ·  W06: An introduction to Alexandria


  15.21.  Log4j

  This package provides a logging framework that Java applications can
  use.  It can be enabled at runtime without modifying the binary and
  has been designed with performance in mind. It can be found here
  <http://jakarta.apache.org/log4j/docs/index.html>



  16.  XML projects

  Directly from the Apache XML project website, its goals are:

  ·  To provide commercial-quality standards-based XML solutions that
     are developed in an open and cooperative fashion.

  ·  To provide feedback to standards bodies (such as IETF and W3C) from
     an implementation perspective.

  ·  To be a focus for XML-related activities within Apache projects

  The project homepage is located at .  It is an umbrella for a variety
  of subprojects.


  16.1.  Introduction to XML

  This is a quick introduction to XML. To know more about XML, a good
  starting point is . XML is a markup language (think HTML) for
  describing structured content using tags and attributes. Once content
  is separated from presentation, you can choose how to display
  (cellphone, html, text) or exchange it. The XML standard only
  describes how the tags and attributes can be arranged, not its names
  of what they mean.  Apache provides the tools described in the
  following sections.


  16.2.  Xerces

  The Xerces project provides XML parsers for a variety of languages,
  including Java, C++ and Perl. The Perl bindings are based on the C++
  sources.  There are Tcl bindings for Xerces in the 2.0 version of
  TclXML <http://www.zveno.com/>, by Steve Ball. This 2.0 version is
  only available at the moment thru Ajuba CVS repository
  <http://dev.ajubasolutions.com/software/tcltk/netcvs.html>.  A XML
  parser is a tool used for programatic access to XML documents.  This
  is a description of the standards supported by Xerces:

  ·  DOM <http://www.w3.org/TR/1998/REC-DOM-Level-1-19981001/level-one-
     core.html>: DOM stands for Document Object Model. XML documents are
     hierarchical by nature (nested tags). XML documents can be accessed
     thru a tree like interface. The process is as follow:

  ·  Parse document

  ·  Build tree

  ·  add/delete/modify nodes

  ·  Serialize tree

  ·  SAX <http://www.megginson.com/SAX/index.html>:Simple API for XML.
     This is a stream based API. This means that we will receive
     callbacks as elements are encountered. These callbacks can be used
     to construct a DOM tree for example.

  ·  XML Namespaces <http://www.w3.org/TR/REC-xml-names/>

  ·  XML Schema: The XML standard provides the syntax for writing
     documents. XML Schema provides the tools for defining the contents
     of the XML document (semantics). It allows to define that a certain
     element in the document must be an integer between 10 and 20, etc.

     The Xerces XML project initial code base was donated by IBM. You
     can find more information in the Xerces Java
     <http://xml.apache.org/xerces-j/index.html>, Xerces C
     <http://xml.apache.org/xerces-c/index.html> and Xerces Perl
     <http://xml.apache.org/xerces-p/index.html> homepages.


  16.3.  Xalan

  Xalan is an XSLT processor available for Java and C++.  XSL is a style
  sheet language for XML. The T is for Transformation. XML is good at
  storing structured data (information). We sometimes need to display
  this data to the user or apply some other transformation.  Xalan takes
  the original XML document, reads transformation configuration
  (stylesheet) and outputs HTML, plain text or another XML document.
  You can learn more about Xalan at the Xalan Java
  <http://xml.apache.org/xalan/index.html> and Xalan C
  <http://xml.apache.org/xalan-c/index.html> project homepages.
  16.4.  FOP

  From the website FOP is a Java application that reads a formatting
  object tree and then turns it into a PDF document. So FOP takes an XML
  document and outputs PDF, in a similar way that Xalan does with HTML
  or text. You can learn more about FOP here
  <http://xml.apache.org/fop>.



  16.5.  Cocoon

  Cocoon leverages other Apache XML technologies like Xerces, Xalan and
  FOP to provide a comprehensive publishing framework. Cocoon is based
  around XML and XSL and targeted to sites of medium - high complexity.
  It separates content, logic and presentation as described in the
  website:

  ·  XML creation: the XML file is created by the content owners.  They
     do not require specific knowledge on how the XML content is further
     processed rather than the particular chosen DTD/namespace.  This
     layer is always performed by humans directly through normal text
     editors or XML-aware tools/editors.

  ·  XML process generators: the logic is separated from the content
     file.

  ·  XSL rendering: The created document is then rendered by applying an
     XSL stylesheet to it and formatting it to the specified resource
     type (HTML, PDF, XML, WML, XHTML)

     You can learn more about Cocoon at the project homepage
     <http://xml.apache.org/cocoon/index.html>



  16.6.  Xang

  The goal of the Xang project is make it easy for developers to build
  commercial quality XML aware applications for the Web. The application
  logic is defined in a hierarchical XML file which can be scripted via
  JavaScript. This file defines how to access the data (which can be
  other XML files, Java plug-ins, etc.). The Xang engine takes care of
  mapping HTTP requests to the appropriate handlers.  You can learn more
  about Xang at the project homepage
  <http://xml.apache.org/xang/samples.html>.

  16.7.  SOAP

  Apache SOAP ("Simple Object Access Protocol") is an implementation of
  the SOAP submission <http://www.w3.org/TR/SOAP> to W3C.  It is based
  on, and supersedes, the IBM SOAP4J implementation.

  From the draft W3C specification: SOAP is a lightweight protocol for
  exchange of information in a decentralized, distributed environment.
  It is an XML based protocol that consists of three parts:

  ·  An envelope that defines a framework for describing what is in a
     message and how to process it,

  ·  a set of encoding rules for expressing instances of application-
     defined datatypes,

  ·  and a convention for representing remote procedure calls and
     responses.
     Think of SOAP as an XML based remote procedure call or CORBA
     system. It is based on HTTP and XML. In one hand this means it is
     verbose and slow compared to other systems. On the other hand it
     eases interoperatibility, debugging and development of clients and
     servers for a variety of languages (C, Java, , Perl, Python, Tcl,
     etc.) since most modern languages have HTTP and XML modules. You
     can learn more at the Apache SOAP homepage
     <http://xml.apache.org/soap/>

  Related talk

  ·  W02: Rub-a-dub-dub-dubya: SOAP and the Web


  16.8.  Batik

  Batik is a Java based toolkit for applications that want to use images
  in the Scalable Vector Graphics (SVG) <http://www.w3.org/TR/SVG/>
  format for various purposes, such as viewing, generation or
  manipulation.

  It is XML centric and compliant with the W3C specification. It is a
  bit atypical from other Apache projects, in that it provides a
  graphical component. Batik provides hooks to extend the framework thru
  custom tags and it allows conversion from SVG to other formats like
  JPEG or PNG.

  Batik homepage <http://xml.apache.org/batik/index.html>

  Related talk

  ·  W14: Introduction to the Batik project.


  16.9.  Crimson

  It is an alternative, Java-based, XML parser with support for XML 1.0
  thru a variety of interfaces. It is the parser currently shipping in
  Sun products, and an intermediate step until the version 2 of Xerces
  is released.

  Crimson homepage <http://xml.apache.org/crimson/index.html>


  Related talk

  ·  TH08: Java API for XML processing (JAXP) version 1.1


  16.10.  Other XML projects

  There are other projects based on Apache and XML that do not live
  under the Apache XML umbrella

  ·  mod_xslt <http://modxslt.userworld.com/>.  It is a C based module
     for delivering XML/XSL based content. It has a GPL license.

  ·  AxKit <http://axkit.org> is an XML based Application Server for
     mod_perl and Apache. It allows separation of content and
     presentation.


  Related talk

  ·  TH04: AxKit - An XML Application server for Apache

  17.  Perl

  Perl and Apache make a powerful and popular combination. There are
  several projects that use these two technologies.

  17.1.  Embperl

  Allows embedding of Perl in HTML pages. These pages are processed in
  the server before they are delivered to the client. It is similar to
  ``PHP''.  You can learn more here
  <http://perl.apache.org/embperl/index.html>.

  17.2.  Mason

  The Mason project <http://www.masonhq.com/> embeds Perl in HTML with a
  reusable component model approach. It allows caching, templating, etc.

  17.3.  Mod_Perl

  Mod_perl is one of the most veteran and successful Apache projects. It
  embeds a Perl interpreter in Apache and allows access to the web
  server internals from Perl. This allows for entire modules to be
  written in Perl or a mixture of Perl and C code.  In the 1.3 Apache
  versions, one interpreter has to be embedded in each child, since the
  server is multiprocess based.  In heavy traffic dynamic sites, the
  increased size could make a difference.  Apache 2.0 is
  multithreadeded, as recent versions of Perl are. The next generation
  of mod_perl takes advantage of this and allows for sharing of code,
  data and session state among interpreters. This results in a faster,
  leaner solution.

  Make sure you check also ``Axkit''



  18.  PHP

  From the PHP website <http://www.php.net> website: PHP is a server-
  side, cross-platform, HTML embedded scripting language. PHP is a
  scripting language like Perl, Python or Tcl. It is the most popular
  module for Apache
  <http://www.securityspace.com/s_survey/data/man.200102/apachemods.html>
  and this is due to a variety of reasons:

  ·  Learning curve is quite low

  ·  Great documentation

  ·  Extensive database support

  ·  Modularity

     PHP has a modular design. There are modules that provide support
     for:

  ·  Database connetivity for Oracle, ODBC, mySQL, mSQL, PostgreSQL, MS-
     SQL server... and many more, check the PHP website
     <http://www.php.net>.

  ·  XML support

  ·  File transfer: FTP


  ·  HTTP

  ·  Directory support: LDAP

  ·  Mail support: IMAP, POP3, NNTP

  ·  PDF document generation

  ·  CORBA

     and many more. You only need to compile/use the modules you need.

  PHP can be used with Apache, as an external CGI or with other
  webservers.  It is crossplatform and it runs on most flavors of Unix
  and Windows.

  If you come from a Windows background, you probably have used Internet
  Information Server with Active Server Pages and MS-SQL Server. A
  common replacement in the Unix world for this trio is Apache with PHP
  and mySQL.  Since PHP works:

  ·  with Apache and with Microsoft IIS

  ·  with mySQL and with MS-SQL server

  ·  on Unix an on Windows

     you have a nice migration path from a Microsoft-centric solution to
     more secure, stable, high performance Unix based solutions (like
     FreeBSD <http://www.freebsd.org>, Solaris <http://www.sun.com>,
     Linux <http://www.linux.com> or OpenBSD <http://www.openbsd.com>)



  19.  Python

  Python is an scripting language similar to Perl or Tcl.  Several
  modules embed Python in the Apache web server:

  ·  Mod Python <http://www.modpython.org>

  ·  Mod Snake <http://modsnake.sourceforge.net>: runs both in Apache
     1.3.x and the upcoming 2.0

     Both modules would be useful if you plan on writing Apache modules
     in Python or run existing Python CGIs faster. Mod Snake allows to
     embed Python in HTML , much like ``PHP'' does.


  Related talk:

  ·  F08: mod_snake: Boosting productivity with Python


  20.  Tcl

  The Tcl Apache project <http://tcl.apache.org> integrates Tcl with the
  Apache webserver. Tcl is a lightweight, extensible scripting language.
  You can learn more about Tcl here <http://dev.ajubasolutions.com/>.
  There are several modules currently under the Apache Tcl umbrella:

  ·  Mod_dtcl <http://tcl.apache.org/mod_dtcl/> allows for embedding Tcl
     on HTML pages like ``PHP'' does.

  ·  Neowebscript <http://tcl.apache.org/neowebscript/> takes a similar
     approach
  ·  Mod_tcl <http://www.fractal.net/mod_tcl.tm/> takes an approach
     similar to mod_perl and runs both in 1.3.x and 2.x versions of
     Apache.

     Other Tcl Apache project can be found at WebSH <http://websh.com/>.


  21.  Modules for other languages

  This document have described modules for popular server side languages
  such as Perl, Python, PHP. You can find additional language modules
  (JavaScript, Haskell, etc.)  at the Apache modules directory
  <http://modules.apache.org>.


  22.  Apache 2.0

  The current version of Apache (the 1.3 series) is process based. That
  means that the server forks itself a number of times to answer
  simultaneous requests.  The children are isolated from each other.
  This is reliable: if a module misbehaves, the parent process kills
  that child and it only affects the request being served, not the
  server as a whole.  Threads are similar to lightweight processes.
  Threads can share common data.  If a thread misbehaves it can corrupt
  other threads and the server as a whole can go down. On the other
  hand, the thread model allows for faster, leaner webservers. Apache
  2.0 brings the best of both worlds, allowing the user to define number
  of processes and number of threads per process. Apache 2.0 introduces
  APR, the Apache Portable Runtime, which increases even more Apache's
  portability.  Finally, layered I/O brings a new level of modularity to
  Apache development.



  23.  Migrating from Netscape (iPlanet) web servers

  The bulk of the work may reside in converting custom modules from
  NSAPI to the Apache API.  Nearly all the other server side
  technologies (Java, Perl, CGIs) should be portable with little or no
  change.  Netscape is tightly integrated with LDAP servers. You may be
  also interested in LDAP modules in .  Netscape includes server side
  JavaScript support, you can check the Apache equivalent,
  mod_javascript
  <http://www.geocities.com/TimesSquare/Fortress/9743/binjs.html>.


  24.  Migrating from Microsoft IIS

  Common reasons why people migrate from IIS to Apache (and not the
  other way around) include stability, performance and security. This is
  partly because most people running Apache do it on an Unix variant
  (like Solaris, FreeBSD or Linux). Fortunately, Apache is multiplatform
  and runs on both Unix and Windows, offering a sensible migration path.

  Common Windows based web development environments like Coldfusion or
  Active Server Pages have Unix ports or compatible environments (some
  are commmercial, some are freely available):

  ·  Coldfusion for Linux <http://www.allaire.com/Products/coldfusion/>

  ·  Perl ASP module <http://www.apache-asp.org/>

  ·  Halcyon ASP <http://www.halcyonsoft.com/>


  ·  OpenASP <http://www.activescripting.org/>

     Apache for Windows supports also the ISAPI interface.

  If you want to go for a complete open source solution and you come
  from a Windows background ( IIS + ASP + MS-SQL server) the roughly
  equivalent (and highly popular) combination is Apache + PHP + MySQl
  <http://www.mysql.com> or PostgresSQL <http://www.postgresql.org>.
  You can learn more about PHP ``here''

  Support for Windows is greatly improved in the new 2.0 Apache version,
  still in beta stage at the time of this writing.



  25.  Links

  Additional Apache related resources

  25.1.  Websites


  ·  Apache <http://www.apache.org>

  ·  Apache modules directory <http://modules.apache.org>

  ·  Apache today <http://www.apachetoday.com>

  ·  Slashdot Apache section
     <http://slashdot.org/index.pl?section=apache>


  25.2.  Java application servers

  These are open source application servers that build on or are known
  to play well with Apache.

  ·  Resin <http://www.caucho.com/>: Servlets, JSP, XSL

  ·  Enhydra <http://www.enhydra.com/>: Java/XML application server.

  ·  Locomotive <http://www.locomotive.org/>: Servlets, load balancing,
     failover.

  ·  JBoss <http://www.jboss.org/>: Enterprise Java Beans container,
     J2EE

  26.  Contacting the author

  You can contact me at . I welcome suggestions and corrections, but
  please, please, do not send me messages asking me to troubleshoot your
  Apache installation. I just do not have the bandwidth and your mail
  will be most likely ignored. If you need support:

  ·  Check the error logs, read the docs, specially the FAQ
     <http://www.apache.org/docs/misc/FAQ.html>.

  ·  Try comp.infosystems.www.servers.unix at .  Search for a similar
     problem.

  ·  If you are still stuck. Provide as much information as you can,
     relevant error_log entries and steps you have taken so far and post
     to that newsgroup. This will increase the chances someone will
     answer your question

  If you want commercial support, consider contacting Covalent
  <http://www.covalent.net>, which provides expert support for Apache
  (at a fee, of course). If you are using Apache on Linux, your Linux
  vendor may have support plans that include Apache too.


  26.1.  Translations

  If you want to contribute a translation of this document you should
  use the SGML source. Check  for info.  Please drop me a note so I can
  make sure you get the most recent version



