Varnish Cache is a web application accelerator also known as a caching HTTP reverse proxy. You install it in front of any server that speaks HTTP and configure it to cache the contents. Varnish Cache is really, really fast. It typically speeds up delivery with a factor of 300 - 1000x, depending on your architecture. A high level overview of what Varnish does can be read on varnish-cache.org

This extension tells Varnish about TYPO3 insights of a page to allow Varnish make proper caching decisions based on those information. It informs Varnish to invalidate the cache as soon as the content is changed through the TYPO3 backend.

• ready to use configration for Varnish and TYPO3
• Varnish based caching for all pages using cache-tags
• TYPO3 clear cache hook to clear cache or smart ban relevant pages in Varnish

• the extension sets config.sendCacheHeaders = 1 to enable TYPO3 core function which sends appropriate cache headers to Varnish
• send "X-Cache-Tags" HTTP Header which is used to issue PURGE command against
• send appropriate PURGE Command to Varnish during a TYPO3 clearCache action
• those headers are used for Varnish processing only and get removed afterwards

We recommend the installation via composer. Maybe you can use our TYPO3-Composer-Webroot Project

From project root you need to run

composer require dmk/mkvarnish

• you should make yourself familiar with Varnish and how you want to implement Varnish in your specific setup.
• Varnish has to be up and running. You can find a sample configuration in EXT:mkvarnish/Configuration/Varnish/default-4.vcl. Make sure to change or remove the Debug ID at the beginning of sub vcl_recv. Furthermore you should check the last comment in sub vcl_recv and act accordingly.
• requests to all static files should send appropriate expires headers

• set $TYPO3_CONF_VARS['SYS']['reverseProxyIP'] to the IP address which is used by Varnish to connect to your Webserver or enable the caching in the extension configuration by set sendCacheHeaders to Force Enabled.
• do not use sessions, the fe_typo_user cookie will disable the caching
• dont set no_cache=1
• the use of *_INT objects will disable the cache too, dont use it (You can find them with the Admin Panel.)

Sometimes there is a page that should be cached through Varnish but contains USER_INT plugins, for example a news detail page with a comment plugin. To migrate such a plugin to a USER plugin might be a hassle or even impossible. But there is a easy solution: The plugin needs to be lazy loaded with Ajax. To achieve this you can use the Ajax Content Renderer feature of mktools.