Intro to Apache
The web server that revolutionized internet
Lamp
- Architecture to use loosely coupled components
- Linux, Apache, Mysql, php/perl/python
What's a web server
It's what makes the internet run
But you already know that
So can you name a few web servers?
HTTP PRotocol
Http request:
GET /index.html HTTP/1.1
Host: www.example.com
Http response:
HTTP/1.1 200 OK
Date: Mon, 23 May 2005 22:38:34 GMT
Server: Apache/1.3.3.7 (Unix) (Red-Hat/Linux)
Last-Modified: Wed, 08 Jan 2003 23:11:55 GMT
ETag: "3f80f-1b6-3e1cb03b"
Content-Type: text/html; charset=UTF-8
Content-Length: 131
Accept-Ranges: bytes
Connection: close
<head>
<title>An Example Page</title>
</head>
<body>
Hello World, this is a very simple HTML document.
</body>
</html>
Why Apache?
- Its open source
- Its fast, secure and reliable
- It has modular architecture
- Its concurrent
- More than half the internet runs on it.
- Fun fact: the word apache comes from "a patchy server", a reference to its initial beginnings.
High Level ARchitecture
![](http://www.shoshin.uwaterloo.ca/~oadragoi/cw/CS746G/a1/fig1.gif)
Apache Core
- Apache core takes care of the configuration
- Controls the modules
- And takes care of the serving the static content
- Taker care of the logging
Apache Core Architecture
![](http://www.shoshin.uwaterloo.ca/~oadragoi/cw/CS746G/a1/fig2.gif)
Apache MOdules
- Access control: mod_authz_host
- Authorization/Authentication: mod_auth
- Dynamic Content eg. mod_php, mod_fcgi
- Performace: mod_pagespeed,mod_spdy
LoadModule auth_module_modules/mod auth.so
Architecture of apache Module
![](http://www.shoshin.uwaterloo.ca/~oadragoi/cw/CS746G/a1/fig3.gif)
Overall Architecture
![](http://www.shoshin.uwaterloo.ca/~oadragoi/cw/CS746G/a1/fig4.gif)
Concurrency
- For concurrency, apache uses something called multi-processing modules or MPMs
- Each MPMs have different way of managing http requests
- There are 3 most common MPMs for apache , mod_prefork, mod_worker, mod_event
- Only one MPM can be used at a time
MPMs![](https://s3.amazonaws.com/media-p.slid.es/uploads/ayushgoyal/images/499510/1.png)
Apache Start and REstart
- Since apache requires access to port 80, it needs to run as root
- It spawns all the worker/fork process for serving requests (as mentioned in MPMs) as some other user specified in httpd conf
- To restart/reload apache you send signal to the root apache process and it takes care of the child/spawned processes accordingly.
- When apache is restarted, the parent apache is never killed unless you specifically stop it, only the child processes are stopped.
Restart
- apchectl -k restart
- apachectl -k graceful
- the init script /etc/init.d/httpd may behave differently depending upon distribution
STopPing
- similar to graceful restart, we have graceful-stop and normal stop
- they can be invoked via "apachectl -k graceful-stop" and "apachectl -k stop" respectively
- You can read more about starting, restarting and stopping here on apache docs. I have added links in the end.
Configuration Context
- Server config
- Virtualhosts
- Directory/Location/File
- htaccess file
- Allow for serving multiple websites on a single server
- A single server may have thousands of virtualhosts
- Virtual hosts are either IP based, or Name based
- You can define various configuration in the context of a virtualhost
Virtual Hosts
- Name Based
- IP based
mod_php
- Simple module for serving php pages via apache
- Loads up a php interpreter as an apache module
- Has some performance penalties if compared to mod_fcgi but is simple to use if you want to run a small scale website
Some other MOdules
mod_authz_host for access_control
- specify ip based control which sites
mod_rewrite/mod_alias
- map a url to a script or another file
mod_status
- to view info on the server status
Troubleshooting
- two logs access_log and error_log
- access_log contains all the http requests processed by apache
- error_log contains all the errors encountered while handling errors
- we can enhance logs using various modules as well, eg mod_firstbyte
Apache VS Nginx
- Nginx achieves better performance using an event model
- Its asynchronous and tries to do non-blocking IO
- Use multiplexing on different worker processes using underlying implementation using epoll,kqueue
- apache support .htaccess and auth
SOurces
- http://www.shoshin.uwaterloo.ca/~oadragoi/cw/CS746G/a1/apache_conceptual_arch.html
- http://httpd.apache.org/docs/2.2/invoking.html
- http://httpd.apache.org/docs/2.2/stopping.html
- http://aosabook.org/en/nginx.html (Nginx Architecture)
- Previous year's presentation by deepak.b
Intro to Apache
By Ayush Goyal
Intro to Apache
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