Best practices for using the Vary Header

Vary is one of the most powerful HTTP response headers, enabling efficient objection compression, device detection, A/B testing at the edge, and more. Using it incorrectly, however, can have disastrous effects. Seasoned performance veteran and Fastly engineer Rogier “Doc” Mulhuijzen walks you through best practices for using Vary, including use cases and code snippets for putting Vary to work.


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“Used correctly, Vary can do wonderful things. Unfortunately, this header is frequently used incorrectly, which can lead to abysmal hit ratios. Worse still, if it's not used when it should be, the wrong content could be delivered. ”
Rogier "Doc" Mulhuijzen
Senior Professional Services Engineer

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About the author

Rogier "Doc" Mulhuijzen | Fastly, Inc.

Doc is a senior professional services engineer and Varnish wizard at Fastly, where performance tuning and troubleshooting have formed the foundation of his 17-year career. When he’s not helping customers, he sits on the Varnish Governance Board, where he helps give direction and solve issues for the Varnish open source project. Formerly an Oracle DBA and Unix admin, Rogier learned scaling while working for Ziggo, a major Dutch ISP. In his spare time, he likes to conquer all terrains by riding motorcycles, snowboarding, and sailing. Find him on Twitter as @drwilco.