Middleman Netlify HTTP/2 Server Push

config.rb

ready do
  # Insert fingerprinted asset paths into _headers for Netlify.
  proxy "/_headers", "/headers.txt",
    layout: false,
    locals: {
      # these variables will be different for you. Add at will!
      all_css: sitemap.find_resource_by_path('css/all.css'),
      vendor_js: sitemap.find_resource_by_path('js/vendor.js'),
      main_js: sitemap.find_resource_by_path('js/main.js')
    },
    ignore: true
end

headers.txt.erb

# This file goes in your Middleman `source` directory.

# configure HTTP/2 Server Push
/
  Link: <<%= all_css.url %>>; rel=preload; as=style
  Link: <<%= vendor_js.url %>>; rel=preload; as=script
  Link: <<%= main_js.url %>>; rel=preload; as=script

# Set a long cache expiry on asset urls
<%= all_css.url %>
  Cache-Control: public, max-age=31556926
<%= vendor_js.url %>
  Cache-Control: public, max-age=31556926
<%= main_js.url %>
  Cache-Control: public, max-age=31556926