I have
plug Plug.Static,
at: "/pros",
from: :zipbooks,
gzip: true,
cache_control_for_etags: "public, max-age=604800",
only: ~w(css assets fonts images js favicon.ico robots.txt)
and my js
css
and svg
files are being served with content-encoding:gzip
but my png files, served the same way, are not.
Here's an example of an svg and how its gzipped:
and heres a png