Cookies and Varnish¶

Example one: Parsing a custom cookie¶

Acquia Cloud Platform parses a single request cookie prefixed with acquia_extract:. For example, Acquia Cloud Platform parses the incoming content with a Cookie:acquia_extract:WEBSHOP_CART_ID=1234; header into the following headers:

Cookie: WEBSHOP_CART_ID=1234
X-Acquia-Cookie-Key: WEBSHOP_CART_ID
X-Acquia-Cookie-Value: 1234

You can configure your application to provide a Cache-Control: no-cache response header for all requests where the value of X-Acquia-Cookie-Key is WEBSHOP_CART_ID, or to respond with a Vary: X-Acquia-Cookie-Key,X-Acquia-Cookie-Value header to vary the cache. However, it is recommended to avoid more than ten variations of each response. If there are too many variations, the cache fills up, and underperforms or fails. For more information on varying cache by cookie and setting the Vary header on your application’s responses, see Best practices for using the Vary header.

Example two: Passing Acquia-provided cookies¶

Acquia provides the following generic cookies that can be customized with any value useful to your application. The advantage is that these request cookies are converted to headers and therefore, the Varnish cache can be varied on them.

Consider a request that comes to Acquia Cloud Platform with the following cookie header:

Cookie: specific_thing=anything;clicked_banner=0;acquia_a=blue;acquia_b=green;acquia_extract:WEBSHOP_CART_ID=1234;category=shirts;

For the preceding request, the system expands the request headers and sends the following to your application:

X-Acquia-Cookie-Key: WEBSHOP_CART_ID
X-Acquia-Cookie-Value: 1234
X-Acquia-Cookie-A: blue
X-Acquia-Cookie-B: green
Cookie: specific_thing=anything;clicked_banner=0;acquia_a=blue;acquia_b=green;WEBSHOP_CART_ID=1234;category=shirts;

Note that the acquia_extract: is removed from the cookie header value. Your application can decide what to respond with by inspecting the X-Acquia-Cookie-* headers, including the Vary: X-Acquia-Cookie-A option.

Therefore, Acquia Cloud Platform enables you to vary cached content based on some specific cookie values.

Session cookies invalidate Varnish caching¶

Content containing Drupal session cookies are never cached, as they contain personalized information that should not be displayed to other users.

Stripping cookie headers from static assets¶

Certain file types managed by Drupal in the modules, themes, files, or libraries directories have incoming cookie headers removed. For more information, see Stripping cookies from static files.

Troubleshooting cookie values¶

In PHP, $_COOKIE is populated as an array from the values in an incoming request’s Cookie header. To access this array, your application should parse this array during each Drupal request, such as during hook_init. When troubleshooting your application, code similar to the following examples enables you to review the values stored in your cookie array:

• var_dump($_COOKIE);
• print_r($_COOKIE);

For information about retrieving session cookies when troubleshooting, see the Retrieve a session cookie from a one-time login link Acquia Support Knowledge Base article.

Reference material¶

The length of time that a cacheable object is stored in the Varnish cache is determined by the cache control headers, such as Cache-Control and Cache-Control: s-maxage. For more information on controlling cache lifetime, read the following articles:

• Configuring Drupal cache settings for Varnish
• Set max-age headers for specific pages, files, or paths