Caching HTTP alternates

Some origin servers answer requests to the same URL with a variety of objects. The content of these objects can vary, according to whether a server delivers content for different languages, targets different browsers with different presentation styles, or provides different document formats (HTML, PDF). Different versions of the same object are termed alternates and are cached by Content Gateway based on Vary response headers.

Configuring how Content Gateway caches alternates

You can specify additional request and response headers for specific content types that the proxy will identify as alternates for caching.

Navigate to the Configure > Protocols > HTTP > Cacheability tab.

In the Vary Based on Content Type section, click Enabled to cache alternate versions of HTTP documents that do not contain the Vary header.

Specify additional request and response headers for the proxy server to identify:

In the Vary by Default on Text field, enter the HTTP header field on which you want to vary if the request is for text (for example, an HTML document).

In the Vary by Default on Images field, enter the HTTP header field on which you want to vary if the request is for images (for example, a .gif file).

In the Vary by Default on Other Document Types field, enter the HTTP header field on which you want to vary if the request is for anything other than text or images.


	Note If you specify Cookie as the header field on which to vary in the above fields, make sure that the appropriate option is enabled under Dynamic Caching > Caching Response to Cookies. For example, if you enable Caching Response to Cookies > Cache Only Image Types you enable Vary Based on Content Type > Vary by Default on Text, alternates by cookie will not apply to text.

Click Apply.

Limiting the number of alternates for an object

You can limit the number of alternates Content Gateway can cache per object. The default number of alternates is 3.


	Note Large numbers of alternates can affect proxy performance because all alternates have the same URL. Although Content Gateway can look up the URL in the index very quickly, it must scan sequentially through available alternates in the object store.

Navigate to the Configure > Protocols > HTTP > Cacheability tab.

In the Maximum Alternates field, enter the maximum number of alternate versions of an object you want the proxy to cache. The default value is 3.

Click Apply.