Apache The Definitive Guide 3rd Edition



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Apache The Definitive Guide, 3rd Edition
By Ben Laurie, Peter Laurie

Publisher	: O'Reilly
Pub Date	: December 2002
ISBN	: 0-596-00203-3

Updated to cover the changes in Apache's latest release, 2.0, as well as Apache 1.3, this useful guide discusses how to obtain, set up, secure, modify, and troubleshoot the Apache software on both Unix and Windows systems. In addition to covering the installation and configuration of mod_perl and Tomcat, the book examines PHP, Cocoon, and other new technologies that are associated with the Apache web server.

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Preface

Who Wrote Apache, and Why?

The Demonstration Code

Conventions Used in This Book

Organization of This Book

Acknowledgments

Chapter 1. Getting Started

Section 1.1. What Does a Web Server Do?

Section 1.2. How Apache Works

Section 1.3. Apache and Networking

Section 1.4. How HTTP Clients Work

Section 1.5. What Happens at the Server End?

Section 1.6. Planning the Apache Installation

Section 1.7. Windows?

Section 1.8. Which Apache?

Section 1.9. Installing Apache

Section 1.10. Building Apache 1.3.X Under Unix

Section 1.11. New Features in Apache v2

Section 1.12. Making and Installing Apache v2 Under Unix

Section 1.13. Apache Under Windows

Chapter 2. Configuring Apache: The First Steps

Section 2.1. What's Behind an Apache Web Site?

Section 2.2. site.toddle

Section 2.3. Setting Up a Unix Server

Section 2.4. Setting Up a Win32 Server

Section 2.5. Directives

Section 2.6. Shared Objects

Chapter 3. Toward a Real Web Site

Section 3.1. More and Better Web Sites: site.simple

Section 3.2. Butterthlies, Inc., Gets Going

Section 3.3. Block Directives

Section 3.4. Other Directives

Section 3.5. HTTP Response Headers

Section 3.6. Restarts

Section 3.7. .htaccess

Section 3.8. CERN Metafiles

Section 3.9. Expirations

Chapter 4. Virtual Hosts

Section 4.1. Two Sites and Apache

Section 4.2. Virtual Hosts

Section 4.3. Two Copies of Apache

Section 4.4. Dynamically Configured Virtual Hosting

Chapter 5. Authentication

Section 5.1. Authentication Protocol

Section 5.2. Authentication Directives

Section 5.3. Passwords Under Unix

Section 5.4. Passwords Under Win32

Section 5.5. Passwords over the Web

Section 5.6. From the Client's Point of View

Section 5.7. CGI Scripts

Section 5.8. Variations on a Theme

Section 5.9. Order, Allow, and Deny

Section 5.10. DBM Files on Unix

Section 5.11. Digest Authentication

Section 5.12. Anonymous Access

Section 5.13. Experiments

Section 5.14. Automatic User Information

Section 5.15. Using .htaccess Files

Section 5.16. Overrides

Chapter 6. Content Description and Modification

Section 6.1. MIME Types

Section 6.2. Content Negotiation

Section 6.3. Language Negotiation

Section 6.4. Type Maps

Section 6.5. Browsers and HTTP 1.1

Section 6.6. Filters

Chapter 7. Indexing

Section 7.1. Making Better Indexes in Apache

Section 7.2. Making Our Own Indexes

Section 7.3. Imagemaps

Section 7.4. Image Map Directives

Chapter 8. Redirection

Section 9.1. Security

Section 9.2. Proxy Directives

Section 9.3. Apparent Bug

Section 9.4. Performance

Section 9.5. Setup

Chapter 10. Logging

Section 10.1. Logging by Script and Database

Section 10.2. Apache's Logging Facilities

Section 10.3. Configuration Logging

Section 10.4. Status

Chapter 11. Security

Section 11.1. Internal and External Users

Section 11.2. Binary Signatures, Virtual Cash

Section 11.3. Certificates

Section 11.4. Firewalls

Section 11.5. Legal Issues

Section 11.6. Secure Sockets Layer (SSL)

Section 11.7. Apache's Security Precautions

Section 11.8. SSL Directives

Section 11.9. Cipher Suites

Section 11.10. Security in Real Life

Section 11.11. Future Directions

Chapter 12. Running a Big Web Site

Section 12.1. Machine Setup

Section 12.2. Server Security

Section 12.3. Managing a Big Site

Section 12.4. Supporting Software

Section 12.5. Scalability

Section 12.6. Load Balancing

Chapter 13. Building Applications

Section 13.1. Web Sites as Applications

Section 13.2. Providing Application Logic

Section 13.3. XML, XSLT, and Web Applications

Chapter 14. Server-Side Includes

Section 14.1. File Size

Section 14.2. File Modification Time

Section 14.3. Includes

Section 14.4. Execute CGI

Section 14.5. Echo

Section 14.6. Apache v2: SSI Filters

Chapter 15. PHP

Section 15.1. Installing PHP

Section 15.2. Site.php

Chapter 16. CGI and Perl

Section 16.1. The World of CGI

Section 16.2. Telling Apache About the Script

Section 16.3. Setting Environment Variables

Section 16.4. Cookies

Section 16.5. Script Directives

Section 16.6. suEXEC on Unix

Section 16.7. Handlers

Section 16.8. Actions

Section 16.9. Browsers

Chapter 17. mod_perl

Section 17.1. How mod_perl Works

Section 17.2. mod_perl Documentation

Section 17.3. Installing mod_perl — The Simple Way

Section 17.4. Modifying Your Scripts to Run Under mod_perl

Section 17.5. Global Variables

Section 17.6. Strict Pregame

Section 17.7. Loading Changes

Section 17.8. Opening and Closing Files

Section 17.9. Configuring Apache to Use mod_perl

Chapter 18. mod_jserv and Tomcat

Section 18.1. mod_jserv

Section 18.2. Tomcat

Section 18.3. Connecting Tomcat to Apache

Chapter 19. XML and Cocoon

Section 19.1. XML

Section 19.2. XML and Perl

Section 19.3. Cocoon

Section 19.4. Cocoon 1.8 and JServ

Section 19.5. Cocoon 2.0.3 and Tomcat

Section 19.6. Testing Cocoon

Chapter 20. The Apache API

Section 20.1. Documentation

Section 20.2. APR

Section 20.3. Pools

Section 20.4. Per-Server Configuration

Section 20.5. Per-Directory Configuration

Section 20.6. Per-Request Information

Section 20.7. Access to Configuration and Request Information

Section 20.8. Hooks, Optional Hooks, and Optional Functions

Section 20.9. Filters, Buckets, and Bucket Brigades

Section 20.10. Modules

Chapter 21. Writing Apache Modules

Section 21.1. Overview

Section 21.2. Status Codes

Section 21.3. The Module Structure

Section 21.4. A Complete Example

Section 21.5. General Hints

Section 21.6. Porting to Apache 2.0

Appendix A. The Apache 1.x API

Section A.1. Pools

Section A.2. Per-Server Configuration

Section A.3. Per-Directory Configuration

Section A.4. Per-Request Information

Section A.5. Access to Configuration and Request Information

Section A.6. Functions

Colophon

Index

Copyright

Printed in the United States of America.

Published by O'Reilly & Associates, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.

O'Reilly & Associates books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles (http://safari.oreilly.com). For more information, contact our corporate/institutional sales department: (800) 998-9938 or [email protected].

Nutshell Handbook, the Nutshell Handbook logo, and the O'Reilly logo are registered trademarks of O'Reilly & Associates, Inc. Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and O'Reilly & Associates, Inc. was aware of a trademark claim, the designations have been printed in caps or initial caps. The association between the image of Appaloosa horse and the topic of Apache is a trademark of O'Reilly & Associates, Inc.

While every precaution has been taken in the preparation of this book, the publisher and authors assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein.

Preface

Apache: The Definitive Guide, Third Edition, is principally about the Apache web-server software. We explain what a web server is and how it works, but our assumption is that most of our readers have used the World Wide Web and understand in practical terms how it works, and that they are now thinking about running their own servers and sites.

This book takes the reader through the process of acquiring, compiling, installing, configuring, and modifying Apache. We exercise most of the package's functions by showing a set of example sites that take a reasonably typical web business — in our case, a postcard publisher — through a process of development and increasing complexity. However, we have deliberately tried to make each site as simple as possible, focusing on the particular feature being described. Each site is pretty well self-contained, so that the reader can refer to it while following the text without having to disentangle the meat from extraneous vegetables. If desired, it is possible to install and run each site on a suitable system.

Perhaps it is worth saying what this book is not. It is not a manual, in the sense of formally documenting every command — such a manual exists on the Apache site and has been much improved with Versions 1.3 and 2.0; we assume that if you want to use Apache, you will download it and keep it at hand. Rather, if the manual is a road map that tells you how to get somewhere, this book tries to be a tourist guide that tells you why you might want to make the journey.

In passing, we do reproduce some sections of the web site manual simply to save the reader the trouble of looking up the formal definitions as she follows the argument. Occasionally, we found the manual text hard to follow and in those cases we have changed the wording slightly. We have also interspersed comments as seemed useful at the time.

This is not a book about HTML or creating web pages, or one about web security or even about running a web site. These are all complex subjects that should be either treated thoroughly or left alone. As a result, a webmaster's library might include books on the following topics:

The Web and how it works
HTML — formal definitions, what you can do with it
How to decide what sort of web site you want, how to organize it, and how to protect it
How to implement the site you want using one of the available servers (for instance, Apache)
Handbooks on Java, Perl, and other languages
Security

Apache: The Definitive Guide is just one of the six or so possible titles in the fourth category.

Apache is a versatile package and is becoming more versatile every day, so we have not tried to illustrate every possible combination of commands; that would require a book of a million pages or so. Rather, we have tried to suggest lines of development that a typical webmaster could follow once an understanding of the basic concepts is achieved.

We realized from our own experience that the hardest stage of learning how to use Apache in a real-life context is right at the beginning, where the novice webmaster often has to get Apache, a scripting language, and a database manager to collaborate. This can be very puzzling. In this new edition we have therefore included a good deal of new material which tries to take the reader up these conceptual precipices. Once the collaboration is working, development is much easier. These new chapters are not intended to be an experts' account of, say, the interaction between Apache, Perl, and MySQL — but a simple beginners' guide, explaining how to make these things work with Apache. In the process we make some comments, from our own experience, on the merits of the various software products from which the user has to choose.

As with the first and second editions, writing the book was something of a race with Apache's developers. We wanted to be ready as soon as Version 2 was stable, but not before the developers had finished adding new features.

In many of the examples that follow, the motivation for what we make Apache do is simple enough and requires little explanation (for example, the different index formats in Chapter 7). Elsewhere, we feel that the webmaster needs to be aware of wider issues (for instance, the security issues discussed in Chapter 11) before making sensible decisions about his site's configuration, and we have not hesitated to branch out to deal with them.

Who Wrote Apache, and Why?

Apache gets its name from the fact that it consists of some existing code plus some patches. The FAQFAQ is netspeak for Frequently Asked Questions. Most sites/subjects have an FAQ file that tells you what the thing is, why it is, and where it's going. It is perfectly reasonable for the newcomer to ask for the FAQ to look up anything new to her, and indeed this is a sensible thing to do, since it reduces the number of questions asked. Apache's FAQ can be found at http://www.apache.org/docs/FAQ.html. thinks that this is cute; others may think it's the sort of joke that gets programmers a bad name. A more responsible group thinks that Apache is an appropriate title because of the resourcefulness and adaptability of the American Indian tribe.

You have to understand that Apache is free to its users and is written by a team of volunteers who do not get paid for their work. Whether they decide to incorporate your or anyone else's ideas is entirely up to them. If you don't like what they do, feel free to collect a team and write your own web server or to adapt the existing Apache code — as many have.

The first web server was built by the British physicist Tim Berners-Lee at CERN, the European Centre for Nuclear Research at Geneva, Switzerland. The immediate ancestor of Apache was built by the U.S. government's NCSA, the National Center for Supercomputing Applications. Because this code was written with (American) taxpayers' money, it is available to all; you can, if you like, download the source code in C from http://www.ncsa.uiuc.edu, paying due attention to the license conditions.

There were those who thought that things could be done better, and in the FAQ for Apache (at http://www.apache.org ), we read:

...Apache was originally based on code and ideas found in the most popular HTTP server of the time, NCSA httpd 1.3 (early 1995).

That phrase "of the time" is nice. It usually refers to good times back in the 1700s or the early days of technology in the 1900s. But here it means back in the deliquescent bogs of a few years ago!

While the Apache site is open to all, Apache is written by an invited group of (we hope) reasonably good programmers. One of the authors of this book, Ben, is a member of this group.

Why do they bother? Why do these programmers, who presumably could be well paid for doing something else, sit up nights to work on Apache for our benefit? There is no such thing as a free lunch, so they do it for a number of typically human reasons. One might list, in no particular order:

They want to do something more interesting than their day job, which might be writing stock control packages for BigBins, Inc.
They want to be involved on the edge of what is happening. Working on a project like this is a pretty good way to keep up-to-date. After that comes consultancy on the next hot project.
The more worldly ones might remember how, back in the old days of 1995, quite a lot of the people working on the web server at NCSA left for a thing called Netscape and became, in the passage of the age, zillionaires.
It's fun. Developing good software is interesting and amusing, and you get to meet and work with other clever people.
They are not doing the bit that programmers hate: explaining to end users why their treasure isn't working and trying to fix it in 10 minutes flat. If you want support on Apache, you have to consult one of several commercial organizations (see Appendix A), who, quite properly, want to be paid for doing the work everyone loathes.

The Demonstration Code

The code for the demonstration web sites referred to throughout the book is available at http://www.oreilly.com/catalog/apache3/. It contains the requisite README file with installation instructions and other useful information. The contents of the download are organized into two directories:

install/

This directory contains scripts to install the sample sites:

install: Run this script to install the sites.
install.conf: Unix configuration file for install.
installwin.conf: Win32 configuration file for install.

sites/

This directory contains the sample sites used in the book.

Conventions Used in This Book

This section covers the various conventions used in this book.

Typographic Conventions

Constant width: Used for HTTP headers, status codes, MIME content types, directives in configuration files, commands, options/switches, functions, methods, variable names, and code within body text; Used in code segments to indicate input to be typed in by the user
Constant width italic: Used for replaceable items in code and text
Italic: Used for filenames, pathnames, newsgroup names, Internet addresses (URLs), email addresses, variable names (except in examples), terms being introduced, program names, subroutine names, CGI script names, hostnames, usernames, and group names

Icons

Text marked with this icon applies to the Unix version of Apache.

Text marked with this icon applies to the Win32 version of Apache.

This icon designates a note relating to the surrounding text.

This icon designates a warning related to the surrounding text.

Pathnames

We use the text convention ... / to indicate your path to the demonstration sites, which may well be different from ours. For instance, on our Apache machine, we kept all the demonstration sites in the directory /usr/www. So, for example, our path would be /usr/www/site.simple. You might want to keep the sites somewhere other than /usr/www, so we refer to the path as ... /site.simple.

Don't type .../ into your computer. The attempt will upset it!

Directives

Apache is controlled through roughly 150 directives. For each directive, a formal explanation is given in the following format:

Directive

Syntax
Where used

An explanation of the directive is located here.

So, for instance, we have the following directive:

ServerAdmin

ServerAdmin email address
Server config, virtual host

ServerAdmin gives the email address for correspondence. It automatically generates error messages so the user has someone to write to in case of problems.

The Where used line explains the appropriate environment for the directive. This will become clearer later.

Organization of This Book

The chapters that follow and their contents are listed here:

Chapter 1: Covers web servers, how Apache works, TCP/IP, HTTP, hostnames, what a client does, what happens at the server end, choosing a Unix version, and compiling and installing Apache under both Unix and Win32.
Chapter 2: Discusses getting Apache to run, creating Apache users, runtime flags, permissions, and site.simple.
Chapter 3: Introduces a demonstration business, Butterthlies, Inc.; some HTML; default indexing of web pages; server housekeeping; and block directives.
Chapter 4: Explains how to connect web sites to network addresses, including the common case where more than one web site is hosted at a given network address.
Chapter 5: Explains controlling access, collecting information about clients, cookies, DBM control, digest authentication, and anonymous access.
Chapter 6: Covers content and language arbitration, type maps, and expiration of information.
Chapter 7: Discusses better indexes, index options, your own indexes, and imagemaps.
Chapter 8: Describes Alias, ScriptAlias, and the amazing Rewrite module.
Chapter 9: Covers remote proxies and proxy caching.
Chapter 10: Explains Apache's facilities for tracking activity on your web sites.
Chapter 11: Explores the many aspects of protecting an Apache server and its content from uninvited guests and intruders, including user validation, binary signatures, virtual cash, certificates, firewalls, packet filtering, secure sockets layer (SSL), legal issues, patent rights, national security, and Apache-SSL directives.
Chapter 12: Explains best practices for running large sites, including support for multiple content-creators, separating test sites from production sites, and integrating the site with other Internet technologies.
Chapter 13: Explores the options available for using Apache to host automatically changing content and interactive applications.
Chapter 14: Explains using runtime commands in your HTML and XSSI — a more secure server-side include.
Chapter 15: Explains how to install and configure PHP, with an example for connecting it to MySQL.
Chapter 16: Demonstrates aliases, logs, HTML forms, a shell script, a CGI script in Perl, environment variables, and using MySQL through Perl and Apache.
Chapter 17: Demonstrates how to install, configure, and use the mod_perl module for efficient processing of Perl applications.
Chapter 18: Explains how to install these two modules for supporting Java in the Apache environment.
Chapter 19: Explains how to use XML in conjunction with Apache and how to install and configure the Cocoon set of tools for presenting XML content.
Chapter 20: Explores the foundations of the Apache 2.0 API.
Chapter 21: Describes how to create Apache modules using the Apache 2.0 Apache Portable Runtime, including how to port modules from 1.3 to 2.0.
Appendix A: Describes pools; per-server, per-directory, and per-request information; functions; warnings; and parsing.

In addition, the Apache Quick Reference Card provides an outline of Apache 1.3 and 2.0 syntax.

Acknowledgments

First, thanks to Robert S. Thau, who gave the world the Apache API and the code that implements it, and to the Apache Group, who worked on it before and have worked on it since. Thanks to Eric Young and Tim Hudson for giving SSLeay to the Web.

Thanks to Bryan Blank, Aram Mirzadeh, Chuck Murcko, and Randy Terbush, who read early drafts of the first edition text and made many useful suggestions; and to John Ackermann, Geoff Meek, and Shane Owenby, who did the same for the second edition. For the third edition, we would like to thank our reviewers Evelyn Mitchell, Neil Neely, Lemon, Dirk-Willem van Gulik, Richard Sonnen, David Reid, Joe Johnston, Mike Stok, and Steven Champeon.

We would also like to offer special thanks to Andrew Ford for giving us permission to reprint his Apache Quick Reference Card.

Many thanks to Simon St.Laurent, our editor at O'Reilly, who patiently turned our text into a book — again. The two layers of blunders that remain are our own contribution.

And finally, thanks to Camilla von Massenbach and Barbara Laurie, who have continued to put up with us while we rewrote this book.