This is a large book (1142 pages) and it is the complete Apache HTTP Server Documentation manual, Version 2.5. You can get a free copy of this book as a PDF on apache.org. This book is printed in grayscale.
There is a paperback version - search for ISBN 978-1-68092-148-9.
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. 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.
The Apache HTTP Server ("httpd") was launched in 1995 and it has been the most popular web server on the Internet since April 1996. The Apache HTTP Server is a project of The Apache Software Foundation.