Apache HTTPD Installation and Basic Setup

Apache HTTPD (referred to as Apache) is one of the oldest web servers in the world. It supports a wide variety of operating systems and offers excellent module-based extensibility. This chapter covers installation on Ubuntu, CentOS, Windows, and Docker, along with the directory structure, MPM selection, and service management commands.

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Understanding MPM (Multi-Processing Module)

Before installing Apache, you need to understand MPM. The MPM is the core module that determines how Apache handles requests in parallel.

MPM	Method	Characteristics	Recommended For
Prefork	Multi-process (no threads)	Independent process per request, stable, mod_php compatible	PHP + mod_php
Worker	Multi-process + multi-thread	Better memory efficiency, requires thread-safe modules	Medium scale
Event	Worker improvement (async Keep-Alive)	Manages Keep-Alive connections in a dedicated thread, high performance	** Currently recommended**

# Check currently active MPM
apache2ctl -V | grep MPM
# or
httpd -V | grep MPM

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Ubuntu / Debian Installation

sudo apt update
sudo apt install -y apache2
sudo systemctl start apache2
sudo systemctl enable apache2
sudo systemctl status apache2

After installation, visit http://your-server-ip to see the "Apache2 Ubuntu Default Page."

Change MPM (Prefork → Event)

sudo a2dismod mpm_prefork
sudo a2enmod mpm_event
sudo systemctl restart apache2
apache2ctl -V | grep MPM
# Server MPM: event

Enable SSL Module

sudo a2enmod ssl
sudo systemctl reload apache2

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CentOS / RHEL / Rocky Linux Installation

sudo yum install -y httpd
sudo systemctl start httpd
sudo systemctl enable httpd
sudo firewall-cmd --permanent --add-service=http
sudo firewall-cmd --permanent --add-service=https
sudo firewall-cmd --reload

MPM Configuration (CentOS)

# /etc/httpd/conf.modules.d/00-mpm.conf
# LoadModule mpm_prefork_module modules/mod_mpm_prefork.so
# LoadModule mpm_worker_module modules/mod_mpm_worker.so
LoadModule mpm_event_module modules/mod_mpm_event.so

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macOS Installation (Homebrew)

brew install httpd
brew services start httpd
# Config: /opt/homebrew/etc/httpd/httpd.conf (Apple Silicon)

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Running Apache with Docker

docker run -d --name apache -p 80:80 httpd

docker run -d \
  --name apache \
  -p 80:80 \
  -v $(pwd)/httpd.conf:/usr/local/apache2/conf/httpd.conf:ro \
  -v $(pwd)/html:/usr/local/apache2/htdocs:ro \
  httpd

docker exec apache apachectl graceful

docker-compose.yml:

version: '3.8'
services:
  apache:
    image: httpd:2.4-alpine
    container_name: apache
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - ./conf/httpd.conf:/usr/local/apache2/conf/httpd.conf:ro
      - ./html:/usr/local/apache2/htdocs:ro
    restart: unless-stopped

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Apache Directory Structure

Ubuntu/Debian

/etc/apache2/                     ← Configuration file root
  apache2.conf                    ← Main configuration file
  ports.conf                      ← Listen port settings
  mods-available/                 ← Available modules
  mods-enabled/                   ← Enabled modules (symbolic links)
  sites-available/                ← Virtual host configs (including disabled)
    000-default.conf              ← Default virtual host
  sites-enabled/                  ← Active virtual hosts (symbolic links)
  conf-available/                 ← Additional configs
  conf-enabled/                   ← Active additional configs

/var/www/html/                    ← Default web root
/var/log/apache2/                 ← Log directory
  access.log
  error.log

CentOS/RHEL

/etc/httpd/
  conf/httpd.conf                 ← Main config
  conf.d/                         ← Additional configs (*.conf auto-loaded)
  conf.modules.d/                 ← Module loading configs

/var/www/html/                    ← Default web root
/var/log/httpd/                   ← Log directory

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Service Management Commands

systemctl

sudo systemctl start apache2       # Start
sudo systemctl stop apache2        # Stop
sudo systemctl restart apache2     # Restart (brief connection drop)
sudo systemctl reload apache2      # Graceful reload (zero-downtime, recommended)
sudo systemctl status apache2      # Check status
sudo systemctl enable apache2      # Enable auto-start on boot

apachectl / apache2ctl

sudo apache2ctl graceful           # Graceful restart (completes in-flight requests)
sudo apache2ctl graceful-stop      # Graceful stop
sudo apache2ctl configtest         # Validate configuration syntax
sudo apache2ctl -V                 # Version + compile options
sudo apache2ctl -M                 # List active modules
sudo apache2ctl -S                 # Virtual host summary

Key: Use graceful instead of restart. graceful replaces workers only after in-flight requests complete — zero downtime.

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Summary

Item	Ubuntu	CentOS	Note
Package name	apache2	httpd	Same software
Config root	/etc/apache2/	/etc/httpd/	Different structure
Web root	/var/www/html/	/var/www/html/	Same
Logs	/var/log/apache2/	/var/log/httpd/	Different path
Control command	apache2ctl	apachectl	Same functionality
Recommended MPM	Event	Event	Best performance