Varnish is an open-source reverse proxy that specialises in caching HTTP traffic to speed up web applications.

Who uses this technology?

General usage

Fast page load speed is important for two big reasons. Impatient consumers want a good user experience and search engines use it as an important ranking factor in their search algorithms. Slow pages will chase both away. 

The more complex an application, the more content they have to serve, which makes fast page load speeds even more challenging. Varnish, designed for content-heavy dynamic web applications and APIs, solves this two ways:

Scalability of performance. Reduces the number of HTTP requests that have to be processed by the main server by storing often-used content that doesn’t change frequently, like style sheets and images, in a virtual memory. It also uses separate worker threads for each user request.

Flexible configuration. Varnish uses its own domain-specific language, Varnish Configuration Language, which allows developers to create rules for user requests such as what content should be served, from where it should be served and if any changes should be made to user requests or server responses.

Varnish works well with your CDN and has been known to increase page laid speed 300 – 1000 times!


First released in 2006, Varnish is the most popular caching solution as of 2021:

First released in 2006, Varnish is the most popular caching solution as of 2021:

Source: Wappalyzer

Marketplace benefits

Deliveroo, a service marketplace, is one of the largest food delivery platforms in the world. Stiff competition between delivery service platforms makes the user experience a critical aspect of their value proposition. 

Deliveroo therefore wanted to improve the speed with which users could access and order from restaurant options in their area. They decided to swap their CDN solution for Fastly, a CDN built with Varnish. The result was a 7% improvement in average load times and a 1% increase in conversions, not bad for a company with a £1.2 billion (2020) turnover.

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