Shakapacker hooks up a new shakapacker:compile task to assets:precompile, which gets run whenever you run assets:precompile. If you are not using Sprockets shakapacker:compile is automatically aliased to assets:precompile.

## Heroku

In order for your Shakapacker app to run on Heroku, you'll need to do a bit of configuration before hand.

```bash
heroku create my-shakapacker-heroku-app
heroku addons:create heroku-postgresql:hobby-dev
heroku buildpacks:add heroku/nodejs
heroku buildpacks:add heroku/ruby
git push heroku master

We're essentially doing the following here:

• Creating an app on Heroku
• Creating a Postgres database for the app (this is assuming that you're using Heroku Postgres for your app)
• Adding the Heroku NodeJS and Ruby buildpacks for your app. This allows the npm or yarn executables to properly function when compiling your app - as well as Ruby.
• Pushing your code to Heroku and kicking off the deployment

Your production build process is responsible for installing your JavaScript dependencies before rake assets:precompile. For example, if you are on Heroku, the heroku/nodejs buildpack must run prior to the heroku/ruby buildpack for precompilation to run successfully.

Shakapacker doesn't serve anything in production. You’re expected to configure your web server to serve files in public/ directly.

Some servers support sending precompressed versions of files when they're available. For example, nginx offers a gzip_static directive that serves files with the .gz extension to supported clients. With an optional module, nginx can also serve Brotli compressed files with the .br extension (see below for installation and configuration instructions).

Here's a sample nginx site config for a Rails app using Shakapacker:

upstream app {
  # server unix:///path/to/app/tmp/puma.sock;
}

server {
  listen 80;
  server_name www.example.com;
  root /path/to/app/public;

  location @app {
    proxy_pass http://app;
    proxy_redirect off;

    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
  }

  location / {
    try_files $uri @app;
  }

  location = /favicon.ico { access_log off; log_not_found off; }
  location = /robots.txt  { access_log off; log_not_found off; }

  location ~ /\.(?!well-known).* {
    deny all;
  }

  location ~ ^/(assets|packs)/ {
    gzip_static on;
    brotli_static on; # Optional, see below
    expires max;
    add_header Cache-Control public;
  }
}

If you want to serve Brotli compressed files with nginx, you will need to install the nginx_brotli module. Installation instructions from source can be found in the official google/ngx_brotli git repository. Alternatively, depending on your platform, the module might be available via a pre-compiled package.

Once installed, you need to load the module. As we want to serve the pre-compressed files, we only need the static module. Add the following line to your nginx.conf file and reload nginx:

load_module modules/ngx_http_brotli_static_module.so;

Now, you can set brotli_static on; in your nginx site config, as per the config in the last section above.

If you are using a CDN setup, Shakapacker does NOT use the ASSET_HOST environment variable to prefix URLs for assets during bundle compilation. You must use the SHAKAPACKER_ASSET_HOST environment variable instead (WEBPACKER_ASSET_HOST if you're using any version of Webpacker or Shakapacker before Shakapacker v7).

Make sure you have your public output path (default public/packs), the shakapacker cache path (default tmp/shakapacker) and node_modules in :linked_dirs

append :linked_dirs, "log", "tmp/pids", "tmp/cache", "tmp/sockets", "tmp/shakapacker", "public/packs", ".bundle", "node_modules"

If you have node_modules added to :linked_dirs you'll need to install your JavaScript dependencies before deploy:assets:precompile; you can use package_json to do this generically:

before "deploy:assets:precompile", "deploy:js_install"
namespace :deploy do
  desc "Run rake js install"
  task :js_install do
    require "package_json"
    
    # this will use the package manager specified via `packageManager`, or otherwise fallback to `npm`
    native_js_install_command = PackageJson.read.manager.native_install_command(frozen: true).join(" ")
    
    on roles(:web) do
      within release_path do
        execute("cd #{release_path} && #{native_js_install_command}")
      end
    end
  end
end

You can also replace the use of package_json with the underlying native install command for your preferred package manager.