Preparing compressed (gzipped) Rails assets for Nginx mod_gzip_static

assets.rake

# lib/tasks/assets.rake

namespace :assets do
  ManifestPattern = /^manifest-[0-9a-f]{32}\.json$/
  ExtensionsToCompress = %w{.js .css .json}.freeze

  desc "GZip assets"
  task :compress do
    files = Pathname.glob(Rails.root.join('public/assets/**/*')).map do |file|
      next unless file.extname.in? ExtensionsToCompress
      next if file.basename.to_s =~ ManifestPattern

      gzipped = file.to_s + ".gz"

      next if File.exist? gzipped

      [file, gzipped]
    end.compact

    start = -> item, index {
      gzipped = item.last
      puts "Creating #{gzipped}"
    }

    Parallel.each files, start: start do |file,gzipped|
      Zlib::GzipWriter.open gzipped, Zlib::BEST_COMPRESSION do |dest_io|
        open file, "rb" do |source_io|
          dest_io << source_io.read(16384) until source_io.eof?
        end
      end
    end
  end
end

capistrano.rake

# lib/capistrano/tasks/assets.rake

namespace :deploy do
  desc "Gzip assets"
  task :compress_assets do
    on roles(fetch(:assets_roles)) do
      within release_path do
        with rails_env: fetch(:rails_env) do
          execute :rake, "assets:compress"
        end
      end
    end
  end
end

after "deploy:compile_assets", "deploy:compress_assets"

nginx-site.conf

server {
  # ...

  location ~* ^/assets/ {
    gzip_static on;
    expires max;
    add_header Cache-Control public;
    add_header Last-Modified "";
    add_header ETag "";
    break;
  }
}