Apache Overview HOWTO
Daniel Lopez Ridruejo, ridruejo@apache.org
v0.9, 2002-10-10
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This document gives you an overview of the different Apache projects, such as
the Apache HTTP server and the Tomcat Servlet and JSP engine. It provides
pointers for further information and implementation details.
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1. Introduction
This document gives you an overview of the Apache world, including Apache
Software Foundation projects such as the Apache web server and commercial and
open source third party software. Apache is the most_popular_server_on_the
Internet. New Apache users, especially those coming from a Windows background,
are often unaware of the possibilities of Apache, its 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.
Copyright 2002 Daniel Lopez Ridruejo
Permission is granted to copy, distribute and/or modify this document under the
terms of the Open Content Open Publication License, Version 1.1. A copy of the
license is included in the appendix entitled "Open Content Open Publication
License", or at www.opencontent.org/openpub/.
1.1 Apache Software Foundation
The Apache Software Foundation provides support for the Apache community of
open-source software projects. The Apache projects are characterized by a
collaborative, consensus based development process, an open and pragmatic
software license, and a desire to create high quality software that leads the
way in its field. We consider ourselves not simply a group of projects sharing
a server, but rather a community of developers and users.
The ASF is home to many successful Open Source projects, such as the Tomcat
Servlet/JSP engine and the ANT build tool.
You can learn more about the foundation here.
1.2 Structure of this document
The first part of this document deals with the Apache Web Server and related
modules. It covers the history, architecture and capabilities of the server and
describes ways in which you can extend and customize it.
The second part of this document covers projects of the Apache Software
Foundation, such as those form the Jakarta and Java XML communities. Rather
than organizing the projects around a certain programming language or
technology, they are organized based on functionality provided.
2. Apache
Apache is the leading internet web server, with over 60% market share,
according to the Netcraft_survey. Several key factors have contributed to
Apache's success:
* The Apache_license. It is an open source, BSD-like license that allows for
both commercial and non-commercial uses of Apache.
* Talented community of developers with a variety of backgrounds and an open
development process based on technical merits.
* Modular architecture. Apache users can easily add functionality or tailor
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, Red_Hat and IBM. In addition, Covalent 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
* Yahoo!
* W3_Consortium
* Financial_Times
* Apple
* MP3.com
* Stanford
>From the Apache_website:
The Apache HTTP Server Project is an effort to develop and maintain an open-
source HTTP server for modern operating systems including UNIX and Windows NT.
The goal of this project is to provide a secure, efficient and extensible
server that provides HTTP services in sync with the current HTTP standards.
Apache started its life as modifications to the NCSA Web server, one of the
first HTTP servers. You can learn more about Apache's history here:
The Apache project has grown beyond building just a web server into developing
other critical server side technologies. The Apache Software Foundation,
described in a later section, serves as an umbrella for these projects.
2.1 Architecture
There are two main versions of Apache, the 1.3 series and the 2.0 series.
Although both versions are considered production quality, they differ in
architecture and capabilities.
2.1.1 Apache 1.3
Apache 1.3 has been ported to a great variety of Unix platforms and is the most
widely deployed Web server on the Internet.
Process-based Web server
Apache 1.3 on Unix is a process-based Web server. The Apache program forks
several children at startup. Forking means that a parent process makes
identical copies of itself, called children. Each one of the children can serve
a request independent of the others. This approach has the advantage of
improved stability: If one of the children misbehaves (runs out of control or
has memory leaks) it can be terminated without affecting the others. The
stability comes with a performance penalty. In most Unix operating systems,
creating processes and context switching (assigning processor time to each
process) are expensive operations. Since processes are isolated from each
other, they cannot easily share code and data, consuming system resources.
Windows support
Apache 1.3 is the first version of Apache to support Windows, although the port
is not considered to be as stable as its Unix counterparts. This is due to the
fact that the server had been designed with Unix in mind and the Windows port
was a later addition that did not integrate very well.
Modular
Apache 1.3 has a modular architecture. You can enable or disable modules to add
and remove Web server functionality. You can customize Apache to improve
performance and security. In addition to modules bundled with the server, there
is a great number of third party modules, providing extended functionality.
2.1.2 Apache 2.0
Apache 2.0 is the latest and greatest version of the Apache server. The
architecture contains significant improvements over the 1.3 series. The
following are some of them.
Multi Processing Modules
Apache 2.0 abstracts the request processing architecture in special server
modules, called Multi Processing modules (MPMs). This means that Apache can be
configured to be a pure process-based server, a purely threaded server or a
mixture of those models. Threads are contained inside processes and run
simultaneously. Unlike processes, threads can share data and code. Threads are
thus more "lighweight" than processes, and in most cases threaded servers scale
better than process based servers. The disadvantage is that the server is less
reliable, since if a thread misbehaves it can corrupt data or code belonging to
other threads.
Protocol Modules
The protocol handling has been encapsulated in its own layer in Apache 2.0.
That means it is possible to write modules to serve protocols other than HTTP,
such as POP3 for mail or FTP for file transfer. These protocol modules can take
advantage of a solid server framework and module functionality, such as
authentication and dynamic content generation. This means that, for example,
you can authenticate your POP3 users against the same user database Apache uses
for web requests and that FTP content can be generated dynamically using PHP,
CGI or any other technologies explained later in this document.
Module and filter architecture.
Apache 2.0 maintains the 1.3 modular architecture and adds an additional
extension mechanism: filters. Filters allow modules to modify the content
generated by other modules. They can encrypt, scan for viruses or compress not
only static files but dynamically generated content.
Compatibility issues
Unfortunately, though the module API is similar between versions, they are not
identical and Apache 1.3 modules need to be ported to the new architecture.
Most mainstream modules such as PHP and mod_perl already have Apache 2.0
versions and others, such as mod_dav and mod_ssl, are now part of the server
distribution. Running modules on a threaded architecture requires specific
changes to modules. Modules distributed with Apache have undergone those
changes and are considered `thread-safe', but third-party modules or libraries
may not. If you need one of those, you will be limited to running Apache as a
pure process-based server.
Portable
Apache runs equally well now on Windows and Unix platforms thanks to the Apache
Portable Runtime (APR) library. It abstracts the differences among operating
systems, such as file or network access APIs. Porting Apache to a new platform
is often as simple as porting the Apache Portable Runtime. This abstraction
layer also provides for platform-specific tuning and optimization.
2.2 Security
Apache provides several security-related modules for securing and restricting
access to the server.
Authentication
Authentication modules allow you to determine the identity of a client, usually
by verifying an username and password against a backend database. Apache
includes modules to authenticate against plain text and database files.
Additional authentication modules exist that connect Apache to existing
security frameworks or databases, including: NT Domain controller, Oracle,
mySQL, PostgresSQL and so on.
The LDAP modules are specially interesting, as they allow integration with
company and enterprise wide existing directory services. You can find these
modules at http://modules.apache.org. An Apache 2.0 LDAP module can be found at
the_Apache_website.
Access Control
Apache provides the mod_access module that can restrict access to resources
based on parameters of the client request, such as the presence of a specific
header or the IP address or hostname of the client. Third party modules allow
you to restrict access to clients that misbehave, as explained in later
sections on performance and bandwidth control.
SSL/TLS
The Secure Sockets Layer/Transport Layer Security protocols allow data between
the Web server and client to be encrypted. In Apache 1.3, the protocols are
implemented by mod_ssl, which is distributed separately from the mod_ssl
website and requires applying patches to the server. This was necessary because
of export regulations on encryption. Most of those restrictions have since then
being lifted and starting with Apache 2.0, mod_ssl is now included as a base
module with Apache.
2.3 Proxy
A proxy is a program that performs requests on behalf of another. There are
different kind of Web proxies. A traditional HTTP proxy, also called a forward
proxy, accepts requests from clients (usually Web browsers), contacts the
remote server, and returns the responses.
A reverse proxy is a Web server that is placed in front of other servers,
providing a unified front end and offloading certain tasks, such as SSL
processing, from the backend Web servers.
Apache supports both types of proxy, caching of proxied content and differente
proxy backends such as FTP.
2.4 Performance and scalability
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 and so on. This is
done to prevent abuse.
* mod_mmap: Included in current Apache 1.3 releases, it maps to memory a
statically configured list of files that are frequently requested but
infrequently changed. This functionality is included in mod_file_cache in
Apache 2.
* Mod_bandwidth: This Apache 1.3 module 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: provides bandwidth throttling and balancing by client
IP address. It supports Apache 1.3 and earlier versions of Apache 2.
* Mod_throttle:Throttle bandwidth per virtual host or user. For Apache 1.3
Load Balancing
Using the Apache reverse proxy and mod_rewrite you can have an Apache process
distributing requests among a variety of backend web servers. You can find more
information at http://www.apache.org/docs/misc/rewriteguide.html
Additionally, mod_backhand is an Apache 1.3 module that 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. You can find more
information at http://www.backhand.org/.
Compression
Apache 2.0 includes mod_deflate, a filtering module that compresses content
before delivering it to clients. This saves bandwidth but can have a
performance impact. The mod_gzip_module provides this functionality for Apache
1.3
2.5 CGI scripts
CGI stands for Common Gateway Interface. CGI programs are external programs
that are called when a user requests a certain page. The CGI program receives
information from the web server (form variable values, type of browser, IP
address of the client and so on) and uses that information to output a web page
to the client.
Apache has support for CGIs and there is a third-party Apache 1.3 module that
provides support for the FastCGI protocol. It avoids the performance penalties
associated with starting and stopping a CGI program with every request. You can
find it at http://fastcgi.com/
2.6 Development Platform Integration
Web applications are written in high-level languages such as Java, Perl, C# and
so on and Apache has several modules that integrate them with the server. In
many cases the modules expose the Apache API so entire Apache modules can be
written in those languages.
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. In threaded versions of
Apache 2.0 mod_perl allows for sharing of code, data and session state among
interpreters. This results in a faster, leaner solution.
mod_perl is in itself another platform, with a great variety of modules
available such as Mason and Embperl for embedding Perl in HTML pages and AxKit
for XML-driven templates.
PHP
From the PHP website: PHP is a server-side, cross-platform, HTML embedded
scripting language. It is the most_popular_module_for_Apache 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. Among many others, there are modules that provide
support for:
* Database connetivity for popular databases such as Oracle, MS-SQL server,
ODBC interface, MySQL, mSQL, PostgreSQL and so on.
* XML support
* File transfer: FTP
* HTTP
* Directory support: LDAP
* Mail support: IMAP, POP3, NNTP
* PDF document generation
* CORBA
* SNMP
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 and on Windows
you have a nice, gradual migration path from a Microsoft-centric solution to
Unix based solutions.
Python
Python is a popular object oriented scripting language. Mod_Python, which is
now an official Apache project, allows you to integrate Python with the Apache
web server. You can develop complex web applications or accelerate existing
Python CGI scripts. Recent versions run on Apache 2.0.
Tcl
The Tcl_Apache_project integrates Tcl with the Apache webserver. Tcl is a
lightweight, extensible scripting language. You can learn more about Tcl here.
There are several modules currently under the Apache Tcl umbrella:
* Both Mod_dtcl and Neowebscript allow embedding Tcl on HTML pages. Rivet
combines the best of both modules.
* Mod_tcl takes an approach similar to mod_perl, exposing the Apache API.
* WebSH provides a Tcl Web application environment
Microsoft technologies
Several modules allow integration with Microsoft languages and technologies
such as the .Net framework or Active Server Pages.
.Net
mod_haydn integrates Mono with Apache and exposes the Apache API to the .Net
framework, allowing you to write modules in C#, for example. Covalent provides
mod_asp.net, an commercial Windows module that allows Apache to run ASP.Net
applications, allowing you to replace Microsoft IIS.
ASP
ASP stands for Active Server Pages and is a Microsoft technology that allows
you to embed code, usually Visual Basic, in HTML pages. Several companies such
as ChilliSoft and Stryon provide products that can run ASP applications on Unix
environments.
ISAPI
ISAPI is an API that you can use to extend Microsoft IIS, similarly to how you
would use the Apache API. Apache includes a module mod_isapi that mirrors this
functionality and allows you to run ISAPI modules.
Java
Most applications servers, such as those from Oracle, IBM and BEA provide
modules to integrate with the Apache web server. Additionally, several modules
such as mod_jk and mod_webapp allow you to connect to Tomcat, a Servlet and
JavaServer Pages container that is also part of the Apache Software Foundation.
Modules for other languages
This document has described modules for popular server side languages such as
Perl, Python and PHP. You can find additional language modules (JavaScript,
Haskell, Ruby and others) at the Apache_modules_directory.
2.7 Management
An important part of Web server administration includes building, configuring
and monitoring different servers.
Build tools
Apache can be extended and customized in many different ways. Integration of
different modules with the server can sometimes be a difficult task. Tools such
as the Apache_Toolbox can make this task easier, by providing a menu driven
build framework.
User Interfaces for Apache
Apache is configured thru text configuration files, and that sometimes can be
hard, specially for people coming from a Windows background. There are open
source graphical tools that make this task easier:
* Comanche, by yours truly, is crossplatform and runs on Unix/Linux, Windows
and Mac.
* Webmin: A nice web based interface.
* gui.apache.org: GUI interfaces for Apache project. Programs are in various
degrees of development.
SNMP
SNMP stands for Simple Network Management Protocol. It allows monitoring and
management of network servers, equipment and so on. SNMP modules for Apache
help manage large deployments of web servers, measure the quality of service
offered and integration of Apache with existing management frameworks.
* Open source Mod_SNMP for Apache 1.3.
* Covalent_SNMP provides a commercial SNMP module, support for the latest
SNMPv3 standard, integration with HP-Openview, Tivoli and so on.
2.8 Publishing
Authors of Web content require a means of managing that content and uploading
it to the server. One of the protocols used for this purpose is DAV
(Distributed Authoring and Versioning). DAV is an extension to the HTTP
protocol that enables users and applications to publish and modify Web content.
DAV technology is widely implemented, Microsoft supports it at the operating
system level (WebFolders) and in its Office suite. Same goes for Apple OS-X and
a variety of third party products from Adobe, Oracle and so on. You can get the
mod_dav module for Apache 1.3 at http://www.webdav.org/mod_dav/. In Apache 2.0,
mod_dav is included with the base distribution.
Previous to DAV, Microsoft had its own publishing protocol, integrated with the
Microsoft FrontPage tool. You can add server-side support for Frontpage using
the modules at http://www.rtr.com/Ready-to-Run_Software/, though due to the way
they integrate with Apache they are not considered secure.
2.9 Protocol modules
Apache 2.0 introduced the concept of protocol modules. That means that
developers can reuse the Apache server framework to implement new protocols
such as those dealing with mail and file transfer. mod_ftp is a commercial
Apache-based FTP module from Covalent. mod_pop3 is an open source module that
implements the POP3 protocol, commonly used by mail readers to retrieve
messages from mail servers.
2.10 Virtual Hosting
Apache provides extensive virtual hosting support which means that you can
serve multiple websites from a single server. In Apache 2.0, with the per-child
MPM you can have multiple children, each one serving a different domain under
different Unix user ids. This is very important for security in shared hosting
scenarios, as it allows you to isolate customers from each other. The following
are additional, alternative, virtual hosting modules.
* mod_dynvhost
* mod_pweb
* mod_v2h
2.11 Commercial support
Apache is the web server of choice for many commercial entities, including big
enterprises. These companies have certain requirements when adopting a
technology, specially one that is at the core of their Internet strategy, such
as Web servers. Those requirements include performance, stability, management
capabilities, support, professional services and integration with legacy
systems. A number of commercial companies, such as IBM, Red_Hat and Covalent,
provide the products and services necessary to make Apache meet the needs of
Enterprise customers.
In addition, many other companies and OEMs ship Apache as a bundled web server
with their products.
3. ASF Projects
Although Apache is probably the most popular, the Apache Software Foundation is
home to many other projects. This section provides an overview of the most
relevant ones, organized logically. Most of them belong either to the Jakarta
project and the XML project. The Jakarta project hosts Java-based projects and
the XML project hosts, surprise, XML-related projects.
3.1 Applications and Frameworks
The following are application and development frameworks that are part of the
ASF.
3.1.1 Servers
The following are some ASF server projects.
Tomcat
Tomcat is the flagship product of the Jakarta project. It is the official
reference implementation for the Java Servlet and JavaServer Pages
technologies.
You can learn more in the Tomcat_homepage.
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.
Lucene
Jakarta Lucene is a high-performance, full-featured text search engine written
in Java and part of the Jakarta project. You can find more information at http:
//jakarta.apache.org/lucene/
Jetspeed
Jetspeed is a web based portal written in Java. It has a modular API that
allows aggregation of different data sources (XML, SMTP, iCalendar)
3.1.2 Content management
The following are projects related to content management
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. It also provides a WebDAV server and client
implementation. You can learn more at the Slide_home_page.
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 at http://jakarta.apache.org/alexandria/
index.html
3.1.3 Frameworks
The following are application development frameworks.
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. Some of its features include:
Integration with template systems, MVC style development, Access Control Lists,
localization support and so on. You can find more information at the Turbine
web_site.
Avalon
If you are familiar with Perl or BSD systems, Avalon is roughly the equivalent
of CPAN 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. You
can find more information at the Avalon_web_site.
3.2 Presentation
The following template systems, transformation engines and other presentation
related projects.
Cocoon
Cocoon leverages other Apache XML technologies like Xerces, Xalan and FOP to
provide a comprehensive XML publishing framework. The framework can talk to
many different data sources and can transform the content into several
different delivery formats such as PDF, HTML, XML and RTF. It can run as a
servlet or as a command line program. You can learn more about Cocoon at the
project_homepage
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.
AxKit
AxKit is a popular XML-based Application Server for mod_perl and Apache. It
allows separation of content and presentation and provides on-the-fly
conversion from XML to any format.
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). You 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 and
Xalan_C++ project homepages.
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.
3.3 Parsers and Document Access libraries
The following are different libraries that can be used to parse and manipulate
a variety of document formats.
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. An XML
parser is a tool used for programatic access to XML documents. This is a
description of the standards supported by Xerces:
* DOM: 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 follows:
o Parse document
o Build tree
o add/delete/modify nodes
o Serialize tree
* SAX: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
* 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 or contain an IP address.
The Xerces XML project initial code base was donated by IBM. You can find more
information in the Xerces_Java, Xerces_C++ and Xerces_Perl homepages.
Batik
Batik is a Java based toolkit for applications that want to use images in the
Scalable_Vector_Graphics_(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. You can learn more at
the Batik_homepage
POI
The POI project consists of APIs for manipulating various file formats based
upon Microsoft's OLE 2 Compound Document format using pure Java. This includes
Word and Excel documents. You can find more information at http://
jakarta.apache.org/poi/
3.4 Interoperability
The following are libraries for remote communication and interoperability
between servers.
SOAP
Apache SOAP ("Simple Object Access Protocol") and Axis are implementations of
the SOAP_protocol
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.
Basically you can think of SOAP as an remote procedure call system, based on
HTTP and XML. On the 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 since most modern
languages have HTTP and XML modules. You can learn more at the Apache_SOAP
homepage
XML-RPC
The XML-RPC_project is a Java implementation of the XML-RPC protocol, a light-
weight protocol similar and predecessor to SOAP.
XML security
The XML_security_project provides XML document signature verification for
secure exchange of documents.
3.5 Development
Apache Portable Runtime
The APR project provides a portability layer that abstracts a number of APIs
for file manipulation, network access and so on. It is written in C and works
on most Unix flavors, Windows and a variety of other systems. It is the basis
for Apache 2.0
Ant
Ant is a Java based build tool. It has a modular API and can be extended by
creating new tasks. It is driven by XML configuration files.
Byte Code Library
The Byte_Code_Engineering_Library (BCEL) is a library to analyze, create, and
manipulate binary Java class files.
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 at http://jakarta.apache.org/log4j/
ORO and Regexp
ORO is a complete package that provides regular expression support for Java. It
includes Perl5 regular expression support, glob expressions and so on. All
under the Apache license. You can learn more about ORO at http://
jakarta.apache.org/oro/index.html. There is another ASF lightweight regular
expression package, Regexp.
Struts
Struts is an Apache project that tries to bring the Model-View-Controller (MVC)
design paradigm to web development. It builds on Servlet and JavaServer_Pages
technologies. The model part is made up of Java server objects, which represent
the internal state of the application. The view part is constructed via
JavaServer Pages (JSP), which is a combination of static HTML/XML and Java.
JSPs also allow the developer to define new tags. The controller part consists
of 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.
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 (i.e. date), SQL
database access and so on.
You can learn about TagLibs at http://jakarta.apache.org/taglibs/. More
documentation is included in the package.
Database
OJB is a database mapping tool that allows persistance and storage of Java
objects in relational databases. Xindice is a native XML database for storing
and querying XML documents.
Commons
The Commons_project provides a great variety of reusable Java components with
minimal dependencies.
3.6 Testing
The following ASF projects cover testing and performance analisys.
httpd-test
The httpd-test_project provides a testing framework for the Apache web server
and tools such as flood for HTTP load testing.
Cactus
Cactus is a testing framework for testing server side Java code such as
Servlets and EJBs.
JMeter
This is a testing tool written in Java with a GUI frontend. It can be obtained
at http://jakarta.apache.org/jmeter/.
Lakta
Lakta is an end-to-end HTTP testing tool
Watchdog
The Watchdog_project is a suite of validation sets for the Servlet and
JavaServer Pages specification.
4. Where to find more information
Additional Apache related resources
4.1 Websites
The following are some useful websites
* Apache_Website
* Apache_Week
* Apache_modules_directory
* Apache_today
* Apache_World
* Slashdot_Apache_section
4.2 Books
I maintain a_list_of_books related to this document. It is not a comprehensive
list, but rather I include only those books that I have personally found well-
written and useful.
4.3 Support forums
You can find the Apache users mailing list at http://httpd.apache.org/
lists.html. Similar lists exist for the rest of projects mentioned there. Make
sure you read the Frequently Asked Questions document before posting . You can
also get support in the newsgroup comp.infosystems.www.servers.unix at http://
groups.google.com.
If you want commercial support, consider contacting Covalent, 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.
5. Contacting the Author
You can contact me at daniel @ rawbyte.com . 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 time to answer
people individually. If you need support, please refer to the resources
mentioned above.
5.1 Translations
If you want to contribute a translation of this document you should use the
SGML source. Check http://www.tldp.org for info. Please drop me a note so I can
make sure you get the most recent version.
6. Open Content Open Publication License
Open Publication License Draft v1.0, 8 June 1999 (text version)
6.1 REQUIREMENTS ON BOTH UNMODIFIED AND MODIFIED VERSIONS
The Open Publication works may be reproduced and distributed in whole or in
part, in any medium physical or electronic, provided that the terms of this
license are adhered to, and that this license or an incorporation of it by
reference (with any options elected by the author(s) and/or publisher) is
displayed in the reproduction.
Proper form for an incorporation by reference is as follows:
Copyright (c) <year> by <author's name or designee>. This material may be
distributed only subject to the terms and conditions set forth in the Open
Publication License, vX.Y or later (the latest version is presently available
at http://www.opencontent.org/openpub/). The reference must be immediately
followed with any options elected by the author(s) and/or publisher of the
document (see section VI).
Commercial redistribution of Open Publication-licensed material is permitted.
Any publication in standard (paper) book form shall require the citation of the
original publisher and author. The publisher and author's names shall appear on
all outer surfaces of the book. On all outer surfaces of the book the original
publisher's name shall be as large as the title of the work and cited as
possessive with respect to the title.
6.2 COPYRIGHT
The copyright to each Open Publication is owned by its author(s) or designee.
6.3 SCOPE OF LICENSE
The following license terms apply to all Open Publication works, unless
otherwise explicitly stated in the document.
Mere aggregation of Open Publication works or a portion of an Open Publication
work with other works or programs on the same media shall not cause this
license to apply to those other works. The aggregate work shall contain a
notice specifying the inclusion of the Open Publication material and
appropriate copyright notice.
SEVERABILITY. If any part of this license is found to be unenforceable in any
jurisdiction, the remaining portions of the license remain in force.
NO WARRANTY. Open Publication works are licensed and provided "as is" without
warranty of any kind, express or implied, including, but not limited to, the
implied warranties of merchantability and fitness for a particular purpose or a
warranty of non-infringement.
6.4 REQUIREMENTS ON MODIFIED WORKS
All modified versions of documents covered by this license, including
translations, anthologies, compilations and partial documents, must meet the
following requirements:
* 1. The modified version must be labeled as such.
* 2. The person making the modifications must be identified and the
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* 3. Acknowledgement of the original author and publisher if applicable must be
retained according to normal academic citation practices.
* 4. The location of the original unmodified document must be identified.
* 5. The original author's (or authors') name(s) may not be used to assert or
imply endorsement of the resulting document without the original author's (or
authors') permission.
6.5 GOOD-PRACTICE RECOMMENDATIONS
In addition to the requirements of this license, it is requested from and
strongly recommended of redistributors that:
* 1. If you are distributing Open Publication works on hardcopy or CD-ROM, you
provide email notification to the authors of your intent to redistribute at
least thirty days before your manuscript or media freeze, to give the authors
time to provide updated documents. This notification should describe
modifications, if any, made to the document.
* 2. All substantive modifications (including deletions) be either clearly
marked up in the document or else described in an attachment to the document.
* 3. Finally, while it is not mandatory under this license, it is considered
good form to offer a free copy of any hardcopy and CD-ROM expression of an
Open Publication-licensed work to its author(s).
6.6 LICENSE OPTIONS
The author(s) and/or publisher of an Open Publication-licensed document may
elect certain options by appending language to the reference to or copy of the
license. These options are considered part of the license instance and must be
included with the license (or its incorporation by reference) in derived works.
A. To prohibit distribution of substantively modified versions without the
explicit permission of the author(s). "Substantive modification" is defined as
a change to the semantic content of the document, and excludes mere changes in
format or typographical corrections.
To accomplish this, add the phrase `Distribution of substantively modified
versions of this document is prohibited without the explicit permission of the
copyright holder.' to the license reference or copy.
B. To prohibit any publication of this work or derivative works in whole or in
part in standard (paper) book form for commercial purposes is prohibited unless
prior permission is obtained from the copyright holder.
To accomplish this, add the phrase 'Distribution of the work or derivative of
the work in any standard (paper) book form is prohibited unless prior
permission is obtained from the copyright holder.' to the license reference or
copy.