Apache Basics and simple CGI scripts
Motivation
The web is ubiquitous today. Everything comes with built-in web servers and there are many free/open source web-servers available. For a long time Apache was the most used web server and it is still rather prominent today. It has recently been surpassed by nginx[1] (pronounced: engine-x). Still the versatility of Apache and the time-tested security makes it a good choice for many applications.
Here you will learn the basics to get you started with running an apache web server, yet many of the concepts will apply to any web server.
Appache Configuration
Virtual Web Servers
A web server without encryption answers on port 80. If you have https encryption then it answers on port 443. If you have more then one IP you can choose which IP address the socket binds
to.
When a web client connect they will ask for the URI part (the part behind the host name) but after the request the host name that should be sent is also transmitted (in http/1.1 requests). Thus the server can present different web pages depending on the host name.
So the server can discern what the client wants, either be the IP address and/or by the host name that the client requested. So we speak of IP-based and name-based virtual hosts.
With https protected services there is a little chicken-and-egg type problem: When the SSL connection is established the server needs to present the certificate for that server. If it has more virtual servers it does not know which, since the host name is only sent within the established session. To avoid this and to allow more then one virtual server with https protection on the same IP address the SNI was invented. SNI (server name indication) is supported by all modern browsers. With SNI the server name is already sent within the SSL handshake.
