Tips On Using SubDomain

Wednesday, November 21, 2007 Labels:

Points to consider before using subdomains

Subdomain makes the URLs shorter and nicer. It allows website owners to categorize the
content of the website. It also helps in improving the search engine rankings as most of the search engines treat the subdomain as a separate website address. However, there are certain things to consider before setting up subdomains for your website.

  1. Many web hosting providers do not provide subdomains in their hosting packages. If you have subdomain and want to move your site, you have to choose one which supports subdomains.

  2. Most web hosts charge extra for subdomain setup and maintenance.

  3. If you use cookies in your website, a cookie set from a subdomain cannot be read from the main domain and vice versa because of the security association feature tied to the domain which set it. This is also true for session cookies, where, if the user is logged in on the main site, and then moves to a subdomain, the subdomain site will not be able to access the same session cookie, and will assign a new session (hence forcing the user to login again). However, session persistence across subdomains can be maintained by implementing URL rewriting instead of session cookies.

  4. Your website stats will often not include the statistics of the subdomains. Therefore, you have to setup separate statistics for your subdomains. One of the advantages of using subdomain is that the website can be broken down into smaller pieces without losing the brand image associated with the domain name. The subdomains can be hosted on separate servers in order to reduce the burden on the main domain hosting server.

Sharing cookies among all subdomains

As explained earlier, cookies are not shared among subdomains or between the domain
and the subdomain. In order to set cookies accessible by all subdomains, use the
following techniques:

  1. While writing the cookie, set the cookie domain to ".domain.ext" so that it applies to all subdomains.

  2. If the cookie domain is set to ".domain.ext", it will not be accessible by a user who types in the address without the www before the domain (i.e. http://domain.ext). Therefore, redirect all requests without www to http://www.domain.ext.

There are some reported problems with the above approach. It is safe to set the default cookie with no domain specified and then set another one with domain as ".domain.ext". In this case there is no need for the redirects.

However, remember that session cookies are set by the web server software and you may not have control over how the cookie domain is set.


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