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Telling which ServerAlias your visitor used - useful during merging domains

Someone tells you a website to visit - "go to wellhousemanor.co.uk" they say. And you'll naturally add "www." in front of it, calling up www.wellhousemanor.co.uk rather than wellhousemanor.co.uk ... or perhaps you won't.

Web servers are normally set up by default to respond to a single specific host name - either wellhousemanor.co.uk or www.wellhousemanor.co.uk in the example that I've used above. But then, if you
a) Configure your DNS records for both www.wellhousemanor.co.uk and wellhousemanor.co.uk to point to the same server and
b) add a ServerAlias as well as a ServerName in you virtual host definition:
  ServerName www.wellhousemanor.co.uk
  ServerAlias wellhousemanor.co.uk

you can set up a single web site to respond seamlessly to either name (with or without) the "www.". This process can be taken further so that the same host can respond in the same way to other domain names by adding further DNS records and further ServerAlias-es. I will question how wise it is to do a lot of this, as your content may end up being "diluted" across a lot of domains as far as search engines are concerned, and you may end up loosing visibility. Beware!

Ironically, there may be occasions where you have two host names pointing at the same virtual host, and you want to know which was the one used to access your site by your visitor.

• In a PHP program, you can use the $_SERVER[HTTP_HOST] variable (and there will be equivalents in other languages / Frameworks

• Within your Apache configuration, you can refer to %{HTTP_HOST} - for example, if www.wellhousemanor.co.uk and wellhousemanor.co.uk shared the same virtual host, the following lines in your .htaccess file would allow you to divert requests for anything in the /info directory to another site, provided that the original call was to wellhousemanor.co.uk rather than to www.wellhousemanor.co.uk

  RewriteEngine On
  RewriteCond %{HTTP_HOST} ^wellhousemanor.co.uk$
  RewriteRule ^/info http://www.wellho.net/ [L]


This technique - not well documented elsewhere as far as I can see - may be a great help if you're in the process of merging domains, but still have one or two rather obscure sections of your site / the domains which are still to be integrated under a single name.
(written 2012-01-04, updated 2012-01-07)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
A604 - Web Application Deployment - Apache httpd - virtual hosts
  [4404] Which (virtual) host was visited? Tuning Apache log files, and Python analysis - (2015-01-23)
  [3132] Virtual Hosting with Apache http server - an overall scheme, and avoiding common pitfalls - (2011-01-14)
  [1896] Virtual Hosts and Virtual Servers - (2008-11-20)
  [1687] Virtual Hosting on Apache httpd - a primer example - (2008-06-25)
  [690] Adding Virtual Hosts - (2006-04-19)

A607 - Web Application Deployment - Apache httpd mod_rewrite
  [3862] Forwarding a whole domain, except for a few directories - Apache http server - (2012-09-17)
  [3753] Adding a passcode to a directory - (2012-06-05)
  [3339] Simplest ever proxy configuration? - (2011-06-28)
  [3197] Finding and diverting image requests from rogue domains - (2011-03-08)
  [2981] How to set up short and meaningfull alternative URLs - (2010-10-02)
  [2900] Redirecting a page - silent, temporary or permanent? - (2010-08-03)
  [2773] Dynamically watching your web site via a PHP wrapper - (2010-05-21)
  [2768] Carrying a long URL around - looking for memorable shorts - (2010-05-17)
  [2728] Redirecting a home page using mod_rewrite - (2010-04-17)
  [2555] Bookkeeping - (2009-12-29)
  [2094] If you have a spelling mistake in your URL / page name - (2009-03-21)
  [1954] mod_rewrite for newcomers - (2008-12-20)
  [1778] Pointing all the web pages in a directory at a database - (2008-08-30)
  [1771] More HowTo diagrams - MySQL, Tomcat and Java - (2008-08-24)
  [1731] Apache httpd, MySQL, PHP - installation procedure - (2008-08-01)
  [1636] What to do if the Home Page is missing - (2008-05-08)
  [1381] Using a MySQL database to control mod_rewrite via PHP - (2007-10-06)
  [1376] Choosing between mod_proxy and mod_rewrite - (2007-10-02)
  [1207] Simple but effective use of mod_rewrite (Apache httpd) - (2007-05-27)
  [1009] Passing GET parameters through Apache mod_rewrite - (2006-12-27)
  [1006] Apache httpd and Apache Tomcat together tips - (2006-12-24)
  [934] Clustering, load balancing, mod_rewrite and mod_proxy - (2006-11-21)
  [755] Using different URLs to navigate around a single script - (2006-06-11)
  [631] Apache httpd to Tomcat - jk v proxy - (2006-03-03)

H112 - PHP - Further Web Page and Network Handling
  [4483] Moving from mysql to mysqli - simple worked example - (2015-05-03)
  [4070] Passing variable between PHP pages - hidden fields, cookies and sessions - (2013-04-26)
  [3918] Multiple page web applications - maintaining state - PHP - (2012-11-10)
  [3540] Easy session example in PHP - keeping each customers data apart - (2011-12-06)
  [3432] 3 digit HTTP status codes - what are they, which are most common, which should be a concern? - (2011-09-11)
  [3036] Sending out an email containing HTML from within a PHP page - (2010-11-07)
  [2918] Downloading a report from the web for further local analysis - (2010-08-13)
  [2729] Uploading a document or image to its own URL via a browser - (2010-04-18)
  [2679] How to build a test harness into your PHP - (2010-03-16)
  [2632] Shipping a test harness with your class in PHP - (2010-02-12)
  [1549] http, https and ajp - comparison and choice - (2008-02-22)
  [1518] Downloading data for use in Excel (from PHP / MySQL) - (2008-01-25)
  [1515] Keeping staff up to date on hotel room status - (2008-01-22)
  [1505] Script to present commonly used images - PHP - (2008-01-13)
  [1496] PHP / Web 2 logging - (2008-01-06)
  [1495] Single login and single threaded models - Java and PHP - (2008-01-04)
  [1485] Copyright and theft of images, bandwidth and members. - (2007-12-26)
  [1379] Simple page password protection - PHP - (2007-10-04)
  [1355] .php or .html extension? Morally Static Pages - (2007-09-17)
  [1210] PHP header() function - uses and new restrictions - (2007-05-30)
  [1187] Updating a page strictly every minute (PHP, Perl) - (2007-05-14)
  [1183] Improving searches - from OR to AND? - (2007-05-11)
  [1114] PHP Image upload script - (2007-03-21)
  [936] Global, Superglobal, Session variables - scope and persistance in PHP - (2006-11-21)
  [904] Of course I'll tell you by email - (2006-10-25)
  [847] Image maps for navigation - a straightforward example - (2006-08-28)
  [789] Hot answers in PHP - (2006-07-02)
  [767] Finding the language preference of a web site visitor - (2006-06-18)
  [675] Adding PHP tags to an old cgi program - (2006-04-08)
  [603] PHP - setting sort order with an associative array - (2006-02-13)
  [565] Using PHP to output images, XML, Style sheets, etc - (2006-01-15)
  [542] Morning image, afternoon image - (2005-12-26)
  [537] Daily Image Santafied - (2005-12-22)
  [484] Setting the file name for a downloaded document - (2005-11-03)
  [451] Accessing a page via POST from within a PHP script - (2005-09-26)
  [443] Server side scripting of styles to suit the browser - (2005-09-12)
  [425] Caching an XML feed - (2005-08-26)
  [410] Reading a news or blog feed (RSS) in your PHP page - (2005-08-12)
  [376] What brings people to my web site? - (2005-07-13)
  [372] Time calculation in PHP - (2005-07-08)
  [356] Sudoku helper or sudoku cheat - (2005-06-23)
  [345] Spotting a denial of service attack - (2005-06-12)
  [314] What language is this written in? - (2005-05-17)
  [220] When to use Frames - (2005-02-19)


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Images of the new year in Melksham
Some other Articles
Adding Expect on top of Tcl - what is it and where can I get a training course to learn about it?
Comparing loop commands in Tcl
Trapping errors in Tcl - the safety net that catch provides
Images of the new year in Melksham
Telling which ServerAlias your visitor used - useful during merging domains
First of the year
Initial thoughts - response to GW Rail Franchise Consultation for Wiltshire
What would an appropriate train service on the TransWilts line mean
I wish I was not a special case
How big is a web page these days? Does the size of your pages matter?
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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