Apache Web Server Features

Apache Web Server Features

1. Overview

The Apache HTTP Server (Apache Software Foundation, since 1995) is the most widely deployed open-source web server. It is modular, portable (Unix/Windows), multi-threaded, and configurable through plain-text directives, and it supports both static content and dynamic content via CGI/modules and proxying to application servers.

2. Key Configuration Files (Linux layout)

File / Directory	Purpose
httpd.conf (or apache2.conf)	Main server configuration — global directives, MPM selection, module loading
conf/extra/httpd-vhosts.conf	Virtual host definitions (many sites on one server)
conf/extra/httpd-ssl.conf	HTTPS (SSL/TLS) virtual host on port 443
.htaccess	Per-directory overrides (auth, rewrite, MIME) — checked at request time
mime.types / AddType	File extension → MIME type mapping
logs/access_log, logs/error_log	Request logging and error diagnostics
htdocs/ (DocumentRoot)	Default directory of served static files
bin/apachectl, httpd -k start/stop/restart	Server control script

3. Major Features

Feature	Description
Modularity	Functionality is compiled/loaded as DSO modules (LoadModule) — core is small; add/remove features without recompiling
Multiple MPMs	prefork (process per child), worker (threads), event (async keep-alive) — chosen for the workload
Virtual hosting	Name-based and IP-based — many independent web sites on one machine (<VirtualHost *:80>)
Authentication & authorisation	Basic/Digest auth, .htpasswd, Require user/group, LDAP/OAuth via modules
Access control	Require ip, host allow/deny, URL rewriting gates
SSL/TLS (mod_ssl)	HTTPS on 443, certificates, SNI
URL rewriting (mod_rewrite)	Powerful regex URL manipulation — clean URLs, redirects, gateways
CGI / FastCGI / dynamic handlers	Runs external programs (mod_cgi, mod_fcgid, PHP module)
Proxy (mod_proxy)	Reverse proxy / load balancer to Tomcat, Node, etc. (HTTP, AJP, WebSocket)
Compression & caching	mod_deflate (gzip), mod_cache, mod_expires headers
Logging	Common/combined access log formats, per-vhost logs, error log levels, mod_status server statistics
Content negotiation & multi-language	Serves the variant (language/type) best matching the client's Accept headers
Security	mod_security (WAF), chroot, directory permissions, hotlink protection
Portable & free	Runs on UNIX/Linux/BSD/Windows; open source (Apache Licence 2.0)

4. Important Directives (sample httpd.conf)

ServerRoot      "/etc/httpd"          # top of install tree
Listen          80                    # port(s) to bind
LoadModule      rewrite_module modules/mod_rewrite.so
User            apache
ServerAdmin     webmaster@abc.com
ServerName      www.abc.com:80
DocumentRoot    "/var/www/html"       # served file root
DirectoryIndex  index.html index.php  # default file per directory
ErrorLog        logs/error_log
CustomLog       logs/access_log combined
KeepAlive       On
<Directory "/var/www/html">           # per-directory policy
    Options Indexes FollowSymLinks
    AllowOverride All
    Require all granted
</Directory>
<VirtualHost *:80>                    # name-based virtual host
    ServerName  www.shop.com
    DocumentRoot /var/www/shop
</VirtualHost>

5. Apache vs IIS vs Nginx (one-liner compare)

Aspect	Apache	IIS	Nginx
Platform	Any (open source)	Windows only	Any
Concurrency	MPM processes/threads	Thread pool + kernel	Event-driven
Config	Text files (.conf/.htaccess)	GUI + web.config	Text files
Best at	Flexibility, .htaccess, modules	ASP.NET integration	High-traffic static/reverse proxy

6. Exam Points

• List and explain the important features of the Apache web server — 10 marks (very frequent).
• Explain any five important Apache configuration directives with an example httpd.conf snippet — 7 marks.
• Short notes: virtual hosting, MPMs, mod_rewrite, .htaccess — 3-5 marks.
• Compare Apache with IIS/Nginx — 5 marks.