Contributed by
Kévin Dunglas
in
#59020

Web assets like CSS and JavaScript files can be compressed by up to 90%, which
is why most servers compress them before sending them to clients. The three most
commonly used compression formats for the web are:

• Gzip: a solid multi-purpose format with average compression speed and ratio;
• Brotli: typically produces the smallest output (it was designed specifically
  for web assets) but is slower than the others;
• Zstandard: by far the fastest format for compression and decompression, while
  producing very small outputs (often close to Brotli).

Ideally, you'd use the highest compression level available for each format.
However, CPU usage increases much faster than the reduction in file size, so
maximizing compression isn't always worth the cost.
In modern Symfony applications using AssetMapper or Webpack Encore, assets
are versioned and guaranteed to never change. That's why dynamically compressing
them for every request is inefficient; it means compressing the exact same
content again and again.
Symfony 7.3 introduces a new feature to pre-compress web assets on your
server once and serve the compressed versions to all clients. This saves a lot
of CPU and lets you use the maximum compression level to squeeze every last bit
out of your assets.
If you use AssetMapper, enable the feature by adding this configuration:

# config/packages/asset_mapper.yaml
framework:
asset_mapper:
# ...
precompress:
# possible values: 'brotli', 'zstandard', 'gzip'
format: 'zstandard'

That's it! When you run the asset-map:compile command, all assets will be
compressed using the selected format and its highest compression level. The
compressed files will be stored alongside the originals with an additional
extension (e.g. app-8ec4b11.js will generate app-8ec4b11.js.zstd).
Web servers (FrankenPHP, Caddy, etc.) and services (Cloudflare, etc.) that
support asset pre-compression will automatically use the compressed versions, so
there's nothing else to configure on your server.

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