The open source version of Varnish Cache 4.1x is no longer supported. For existing Varnish customers using Varnish Enterprise this is not an issue. For many open source Varnish Cache users this won’t be a surprise, and you will already have updated. The important point is that continued use of Varnish Cache 4.1 means that you will be going it alone. But you don’t have to.
If you’re familiar at all with Varnish, you know it improves content delivery performance by storing a copy of your content in cache, and every request thereafter is fulfilled by the cached content.
Based on the Step-by-step: Speed Up WordPress with Varnish Software article originally written by Federico G. Schwindt and published on Web Designer Magazine - http://www.webdesignermag.co.uk/ as well as on the Varnish Software blog.
It is now available in the Varnish Web Developer Wiki, specifically under the Varnish with WordPress Tutorials section. As with any other wiki docs you can help us to expand it and keep it up to date. I'm publishing it here in the blog for reference. Read on: