WebPerf Deploying Brotli For Static Content At Dropbox

eva2000 · Apr 8, 2017

Dropbox posted an article on their deployment of Brotli compression for static files at https://blogs.dropbox.com/tech/2017/04/deploying-brotli-for-static-content/

In this blog post, we are going to share our experiences with rolling out Brotli encoding for static content used by dropbox.com, decreasing the size of our static assets by 20% on average. Brotli is a modern lossless compression algorithm based on the same foundations as gzip (LZ77 and Huffman encoding), but improves them with a static dictionary, larger matching windows, and extended context modeling for better compression ratios. We won’t go into much detail on how Brotli works here; if you want to dig deeper into the compression format, you can read a great introduction to Brotli internals by Cloudflare.
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Why Brotli
Before starting any project, we need to ask ourselves whether it is worth the engineering resources involved. In this phase, it also makes sense to investigate alternatives. Here are the two most obvious ones for this project:

Improve gzip compression: LZ77 and Huffman encoding can go a long way (after all Brotli itself is using them under the hood) but there are some architectural limitations that can’t be worked around. For example, the maximum window size is limited by 32kB. Later we’ll discuss how to squeeze an additional 5-10% from the venerable deflate by using pre-compression, alternative libraries, and sometimes even data restructuring, but Brotli does even better.

Use Shared Dictionary Compression: This approach was once taken by one of our engineers, Dzmitry Markovich, while he was at LinkedIn, but it has a number of downsides:

Even though this compression method has been around since 2008 it still lacks support in browsers. You can try comparing the “support matrices” of SDCH and Brotli; basically the former is only supported in Chrome-based browsers. Most server-side setups also lack support for SDCH.

SDCH requires an additional static-build step to periodically update dictionaries. This will become especially complex when one needs to enable SDCH for dynamic, localized content.

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FYI, Centmin Mod Nginx users can deploy Brotli too https://community.centminmod.com/forums/centmin-mod-user-tutorials-guides.50/ using same ngx_brotli module that Dropbox uses/mentioned

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WebPerf Deploying Brotli For Static Content At Dropbox

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