Build & maintain complex distributed systems
October 1–2, 2017: Training
October 2–4, 2017: Tutorials & Conference
New York, NY

The Vary header and the future of cache variation at the edge

Andrew Betts (Fastly)
11:35am12:15pm Tuesday, October 3, 2017
Average rating: *****
(5.00, 2 ratings)

Who is this presentation for?

  • Web operations engineers, SREs, and application architects

Prerequisite knowledge

  • An understanding of the mechanics of the HTTP protocol

What you'll learn

  • Gain a clear understanding of the full function and nuance of Vary
  • Discover common mistakes made when using Vary
  • Explore the implications of the new Key spec and use cases for Vary and Key


The Vary header has long been a vital tool for website owners to make content cacheable even if it changes based on inputs other than the URL. The problem is this tool is typically either severely underused, usually limited to Accept-Encoding variation, or is used very badly, resulting in a complete destruction of the cache potential of the page.

Now the IETF is bringing forward a new standard, Key, which aims to provide a more powerful replacement for Vary. Andrew Betts examines the common misconceptions about Vary, the resulting common misconfigurations and how to fix them, advanced use cases for Vary that vastly increase the efficiency of content distribution, and the changes Key will bring about. Along the way, Andrew also considers whether Key actually fails to cater to some of the current use cases for Vary.

Photo of Andrew Betts

Andrew Betts


Andrew Betts is principal developer advocate at Fastly. Andrew’s area of expertise is emerging web technologies, particularly on mobile and tablet platforms. Previously, he was a PHP and JavaScript developer, web standards advocate, and founder of FT Labs, an emerging web technologies division of the Financial Times, where he and his team created the FT web app, one of the best examples of what can be achieved with HTML5.