Exove Ltd is developing a new module, integrating Varnish into Drupal in a way that allows caching not only anonymous users' content, but authenticated users' content as well.
The basic idea behind the module is to generate cacheable anonymous versions from any page with cacheable content, leaving placeholders in place of user specific content, and to serve those versions to all users. Any user-specific content is then replaced with AJAX for all authenticated users.
This module is designed to be used on sites where there are a lot of simultaneous authenticated users, and where caching the content just for the anonymous users isn't enough. Custom code is required to let Cache Control know what content is cacheable and how it should be replaced.
Early versions of the module are already in production use, but the current version at Drupal.org is a work-in-progress; we're actively developing the module to respond to needs by other customers. The module can be currently found in its sandbox here: http://drupal.org/node/1138426/ , and the project approval issue here: http://drupal.org/node/1155312 . The module repository includes an example module that shows how Cache Control can be integrated.
Any comments or feedback are welcome.
