We host multiple sites per server. One issue I ran into recently is when I had a DNS address record (“A” record) pointing to our web server, with a name that’s no longer being served by any VirtualHost.
What was happening was that a site on one of our VirtualHosts was appearing when someone attempted to browse to that address! Obviously, we don’t want any of our sites appearing on a different name than the one that’s been defined as its ServerName.
The issue here is how Apache matches requests to server names. Let’s say that www.example.com points to our web server, but there’s no longer a VirtualHost in Apache with that ServerName. When the user browses to www.example.com, DNS turns that name into an IP address – the IP address of our web server. The request goes to our webserver, asking, “hey, give me www.example.com”.
Apache attempts to find a VirtualHost with a ServerName or ServerAlias that matches www.example.com. If it fails to find a match, Apache serves up the first VirtualHost on that port.
An easy way to deal with this is to define a new VirtualHost to deal with these wayward requests, and put it at the front of the line. VHost configs are loaded in the order of their filenames, so simply creating a “000default” file with a Vhost pointing to a landing page does the trick.