Rogier DocWilco Mulhuijzen

Rogier “DocWilco” Mulhuijzen is a senior professional services engineer and Varnish wizard at Fastly, where performance-tuning and troubleshooting have formed a theme in 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 in 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.

How to leverage the browser cache with a CDN

An introduction to multi-level caching.


Since a content delivery network (CDN) is essentially a cache, you might be tempted not to make use of the cache in the browser, to avoid complexity. However, each cache has its own advantages that the other does not provide. In this post I will explain what the advantages of each are, and how to combine the two for the most optimal performance of your website.

Why use both?

While CDNs do a good job of delivering assets very quickly, they can’t do much about users who are out in the boonies and barely have a single bar of reception on their phone. As a matter of fact, in the US, the 95th percentile for the round trip time (RTT) to all CDNs is well in excess of 200 milliseconds, according to Cedexis reports. That means at least 5% of your users, if not more, are likely to have a slow experience with your website or application. For reference, the 50th percentile, or median, RTT is around 45 milliseconds.

So why bother using a CDN at all? Why not just rely on the browser cache?

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