Install the Magento CDN plugin

Magento 1 storefronts ship thousands of product images through media/, skin/ and js/. Point those three base URLs at a NetDNA pull zone.

1. Pull zone

Origin = Magento base URL. CNAME cdn.store.com to the zone hostname. Enable EdgeSSL if the store is HTTPS.

2. Core Magento config (no plugin)

1. System → Configuration → Web.
2. Unsecure: Base Skin/Media/JS URL = http://cdn.store.com/ (or https if mixed-content-free HTTP is gone).
3. Secure: Base Skin/Media/JS URL = https://cdn.store.com/.
4. Save, flush Magento cache, purge the CDN.

3. Plugin from the 2013 showcase

The NetDNA/MaxCDN Magento extension in the developer showcase writes those URLs for you and can hook purge. Install into app/code/community/, refresh cache, enter API alias / key / secret if the extension talks to the REST API.

4. Do not CDN

Checkout, customer account, /admin. HTML stays on origin.

Magento 2: separate recipe. Comparison: best CDN for Magento.