Why Varnish

Varnish Cache is an open-source HTTP reverse proxy built for one job: keeping web content in memory and serving it as fast as the network allows. It has been in production for twenty years and sits in front of some of the most visited sites on the web. Every site on Edge Caching gets its own dedicated Varnish instance.

What Varnish brings to your sites

Speed

Varnish keeps complete HTTP responses in memory. Serving a cached page involves no PHP, no database query and no disk access: Varnish’s own processing time is measured in microseconds. What your visitors experience is essentially the network round trip, rather than the time WordPress needs to build the page.

Capacity

A single Varnish server can answer tens of thousands of requests per second with modest CPU and memory. Traffic spikes from a newsletter, a news mention or a product launch are absorbed by the cache instead of reaching your server, where they would otherwise exhaust PHP workers and database connections.

Precise control with VCL

Varnish’s behavior is defined in VCL, the Varnish Configuration Language, which is compiled to native code when it is loaded. VCL gives fine-grained control over every request and response: what is cached and for how long, which cookies are removed, which requests go straight to the origin, and which are rejected. On Edge Caching, each site’s VCL is generated from the settings you choose in the admin and reloaded without interrupting traffic.

Availability during outages

Varnish can keep serving cached content after it has expired when the backend server stops responding, a feature called grace mode. Edge Caching builds Always Online on it, so your pages stay available while your server is down or under maintenance. See When your server is down.

Who relies on Varnish

Varnish is used by major platforms, news publishers, universities, open-source projects and content delivery networks. Fastly, one of the largest CDNs, is built on its own version of Varnish, so sites delivered by Fastly are served by Varnish technology as well.

These organizations served their pages through Varnish when checked on October 1, 2026, as shown by their public HTTP response headers:

Category	Organization	How it was verified
Platforms	Wikipedia	Wikimedia cache servers (x-cache: cp… hit), whose in-memory layer is Varnish, as described by Wikimedia engineers at SREcon EMEA 2025
	Reddit	Responses include Via: 1.1 varnish
	Spotify	Responses include Via: 1.1 varnish
News and media	BBC	Responses include Via: 1.1 varnish
	CNN	Responses include Via: 1.1 varnish
	The New York Times	Delivered through Fastly (X-Served-By: cache-…)
	The Guardian	Delivered through Fastly (X-Timer)
	Forbes	Responses include Via: 1.1 varnish
	Vox	Responses include Via: 1.1 varnish
	BuzzFeed	Responses include Via: 1.1 varnish
	Le Monde	Responses include Via: 1.1 varnish
	Le Devoir	Responses include Via: 1.1 varnish
Universities	McGill University	Responses include X-Varnish, from its own Varnish installation
	University of Toronto	Responses include Via: 1.1 varnish, delivered through Pantheon’s Fastly-based CDN
	University of Ottawa	Responses include Via: varnish
Open source	Python.org	Responses include Via: 1.1 varnish
	PyPI, the Python Package Index	Delivered through Fastly (X-Served-By: cache-…)
	Drupal.org	Responses include Via: 1.1 varnish

Check any site yourself

A site’s response headers usually reveal whether Varnish served it:

curl -sI https://www.example.com/ | grep -iE '^(via|x-varnish|x-cache|x-served-by|x-timer):'

Via: … varnish and X-Varnish indicate Varnish directly. X-Served-By: cache-… and X-Timer indicate Fastly’s Varnish-based platform. Sites served by Edge Caching identify themselves with X-Served-By: Layer 7 Edge Caching(TM), along with X-Cache: HIT or MISS.