BP_094_en.md

Host resources (CSS/JS) on a cookie-free domain

Identifiers

GreenIT	V2	V3	V4
73	96	94

Categories

Life cycle	Tiers	Responsible
4. Production	Datacenter	System Administrator

Indications

Priority	Implementation difficulty	Ecological impact
3	3	4

Saved resources
Network

Description

Images, CSS stylesheets, and JavaScript files should be hosted on cookie-free domains. This prevents browsers from sending cookies for each resource when it's not needed. Although transferred with each HTTP request, cookies are useless for static content, as they are used as a link between user browsers and distant application server through the identifiers contained in the text file. It is therefore preferable to store this type of content on a specific domain name such as static.mydomain.com.

Example

Web leaders use a separate domain to serve static resources that do not require cookies. Yahoo!, for example, uses the yimg.com domain, YouTube uses ytimg.com, and Amazon uses images-amazon.com.

Validation rule

The number of ...	is equal to or less than
domains serving static resources WITH a cookie	1