GoodJob is a multithreaded, Postgres-based ActiveJob backend for Ruby on Rails.

GoodJob includes a full-featured (though optional) web dashboard to monitor and administer background jobs. The web dashboard is included in the good_job gem as a mountable Rails Engine.

As the maintainer of GoodJob, I want to make gem development easier for myself by innovating as little as possible. That’s why GoodJob builds on top of Active Record and Concurrent::Ruby.

But, the frontend can be a beast. When thinking about how to build a full-featured web dashboard packaged within a Rails Engine within a gem, I had three goals:

  1. Be asset pipeline agnostic with zero dependencies. As of Rails ~7.0, a Rails developer can choose between several different asset pipeline tools (Sprockets, Webpacker/Shakapacker, esbuild/jsbundling, etc.). That’s too many! I want to ensure what I package with GoodJob is compatible with all of them. I also don’t want to affect the parent application at all; everything must be independent and self-contained.
  2. Allow easy patching/debugging. I want the GoodJob web dashboard to work when using the Git repo directly in a project’s Gemfile or simply bundle open good_job to debug a problem.
  3. Write contemporary frontend code. I want to use Bootstrap UI, Stimulus, Rails UJS, and write modular JavaScript with imports. Maybe even Turbo!

And of course, I want GoodJob to be secure, performant, and a joy to develop and use for myself and the developer community.

Read on for how I achieved it all (mostly!) with GoodJob.

What I didn’t do

Here’s all the things I considered, but decided not to do:

  • Nope: Manually construct/inline a small number of javascript files: I did not want to manually build a javascript file, copy-pasting various various 3rd-party libraries into a single file, and then writing my code at the bottom. This seemed laborious and prone to error, especially when I would need to update a library; and my IDE doesn’t work well with large files so writing my own code would be difficult.
  • Nope: Precompile javascript in the repository or on gem build: I did not want to force a pre-commit step to build javascript, or to only package built javascript into the gem because that would make patching and debugging difficult. Over my career I’ve struggled contributing to a number of otherwise fantastic gems that use this workflow pattern.
  • Nope: Compile javascript in the application: Rails has too many different asset pipeline patterns right now for me to consider supporting them all. I consider this more a result of a highly fragmented frontend ecosystem than an indictment of Rails. I can’t imagine supporting all of the different options and whatever else shows up in the future at the same time. (I’m in awe of the gems that do; nice work rails_admin!)

What I did do

As I wrote earlier: “innovate as little as possible”:

Serve vanilla JS and CSS out of vanilla Routes/Controller

GoodJob has explicit routes for frontend assets that wire up to a controller that serves those assets statically with render :file. Let’s break that down…

In my Rails Engine’s router, I define a namescape, frontend, and two get routes. The first route, modules , is for Javascript modules that will go into the importmap. The second route, static , is for Javascript and CSS that I’ll link/script directly in the HTML head.

# config/routes.rb
scope :frontend, controller: :frontends do
  get "modules/:name", action: :module, as: :frontend_module, constraints: { format: 'js' }
  get "static/:name", action: :static, as: :frontend_static, constraints: { format: %w[css js] }

In the matching controller, I create static constants that define hashes of files that are matched and served, which I store in a app/frontend directory in my Rails Engine. I want paths to be explicit for security reasons because passing any sort of dynamic file path through the URL could be a path traversal vulnerability. All of the frontend assets are stored in app/frontend and served out of this controller:

# app/controllers/good_job/frontends_controller.rb

module GoodJob
  class FrontendsController < ActionController::Base # rubocop:disable Rails/ApplicationController
      css: {
        bootstrap: GoodJob::Engine.root.join("app", "frontend", "good_job", "vendor", "bootstrap", "bootstrap.min.css"),
        style: GoodJob::Engine.root.join("app", "frontend", "good_job", "style.css"),
      js: {
        bootstrap: GoodJob::Engine.root.join("app", "frontend", "good_job", "vendor", "bootstrap", "bootstrap.bundle.min.js"),
        chartjs: GoodJob::Engine.root.join("app", "frontend", "good_job", "vendor", "chartjs", "chart.min.js"),
        es_module_shims: GoodJob::Engine.root.join("app", "frontend", "good_job", "vendor", "es_module_shims.js"),
        rails_ujs: GoodJob::Engine.root.join("app", "frontend", "good_job", "vendor", "rails_ujs.js"),

		# Additional JS modules that don't live in app/frontend/good_job/modules
      application: GoodJob::Engine.root.join("app", "frontend", "good_job", "application.js"),
      stimulus: GoodJob::Engine.root.join("app", "frontend", "good_job", "vendor", "stimulus.js"),

    def self.js_modules
      @_js_modules ||= GoodJob::Engine.root.join("app", "frontend", "good_job", "modules"){}) do |file, modules|
        key = File.basename(file.basename.to_s, ".js").to_sym
        modules[key] = file

    # Necessarly to serve Javascript to the browser
		skip_after_action :verify_same_origin_request, raise: false
    before_action { expires_in 1.year, public: true }

    def static
      render file: STATIC_ASSETS.dig(params[:format].to_sym, params[:name].to_sym) || raise(ActionController::RoutingError, 'Not Found')

    def module
      raise(ActionController::RoutingError, 'Not Found') if params[:format] != "js"

      render file: self.class.js_modules[params[:name].to_sym] || raise(ActionController::RoutingError, 'Not Found')

One downside of this is that I’m unable to use Sass or Typescript or anything that isn’t vanilla CSS or Javascript. So far I haven’t missed that too much; Bootstrap brings a very comprehensive design system and Rubymine is pretty good at hinting Javscript on its own.

Another downside is that I package several hundred kilobytes of frontend code within my gem. This increases the gem size, which is a real bummer if an application isn’t mounting the dashboard. I’ve considered separating the optional dashboard into a separate gem, but I’m deferring that until anyone notices that it’s problematic (so far so good!).

Manually link assets and construct a JS importmaps in my Engine’s layout <head>

Having created the routes and controller actions, I can simply link the static files in the layout html header:

<!-- app/views/layouts/good_job/application.html.erg -->
  <!-- ... -->
  <%# Note: Do not use asset tag helpers to avoid paths being overriden by config.asset_host %>
  <%= rel: "stylesheet", href: frontend_static_path(:bootstrap, format: :css, v: GoodJob::VERSION, locale: nil), nonce: content_security_policy_nonce %>
  <%= rel: "stylesheet", href: frontend_static_path(:style, format: :css, v: GoodJob::VERSION, locale: nil), nonce: content_security_policy_nonce %>
  <%= tag.script "", src: frontend_static_path(:bootstrap, format: :js, v: GoodJob::VERSION, locale: nil), nonce: content_security_policy_nonce %>
  <%= tag.script "", src: frontend_static_path(:chartjs, format: :js, v: GoodJob::VERSION, locale: nil), nonce: content_security_policy_nonce %>
  <%= tag.script "", src: frontend_static_path(:rails_ujs, format: :js, v: GoodJob::VERSION, locale: nil), nonce: content_security_policy_nonce %>

Beneath this, I manually construct the JSON the browser expects for importmaps:

<!-- Link es_module_shims -->
<%= tag.script "", src: frontend_static_path(:es_module_shims, format: :js, v: GoodJob::VERSION, locale: nil), async: true, nonce: content_security_policy_nonce %>

<!-- Construct the importmaps JSON object -->
<% importmaps = GoodJob::FrontendsController.js_modules.keys.index_with { |module_name| frontend_module_path(module_name, format: :js, locale: nil, v: GoodJob::VERSION) } %>
<%= tag.script({ imports: importmaps }.to_json.html_safe, type: "importmap", nonce: content_security_policy_nonce) %>

<!-- Import the entrypoint: application.js -->
<%= tag.script "", type: "module", nonce: content_security_policy_nonce do %> import "application"; <% end %>

That’s it!

I’ll admit, serving frontend assets using render file: is boring, but I experienced a thrill the first time I wired up the importmaps and it just worked. Writing small Javascript modules and using import directives is really nice. I recently added Stimulus and I’m feeling optimistic that I could reliably implement Turbo in my gem’s Rails Engine fully decoupled from the parent application.

I hope this post about GoodJob inspires you to build full-featured web frontends for your own gems and libraries.