Skip to main content
Edit

Node Renderer

The React on Rails Pro Node Renderer replaces ExecJS with a dedicated Node.js server for server-side rendering. It eliminates the limitations of embedded JavaScript execution and provides significant performance improvements for production applications.

Why Use the Node Renderer?​

ExecJS embeds a JavaScript runtime (mini_racer/V8) inside the Ruby process. This works for small apps but creates problems at scale:

  • Memory pressure — V8 contexts consume memory inside each Ruby process, competing with Rails for resources
  • No Node tooling — You cannot use standard Node.js profiling, debugging, or memory leak detection tools with ExecJS
  • Process crashes — JavaScript memory leaks can crash your Ruby server
  • Limited concurrency — ExecJS renders synchronously within the Ruby request cycle

The Pro Node Renderer solves all of these by running a standalone Node.js server that handles rendering requests from Rails over HTTP.

Performance Benefits​

MetricExecJSNode Renderer
SSR throughputBaseline10-100x faster
Memory isolationShared with RubySeparate process
Worker concurrencySingle-threaded per requestConfigurable worker pool
ProfilingNot availableFull Node.js tooling
Memory leak recoveryCrashes RubyRolling worker restarts

At Popmenu (a ShakaCode client), switching to the Node Renderer contributed to a 73% decrease in average response times and 20-25% lower Heroku costs across tens of millions of daily SSR requests.

How It Works​

  1. Rails sends a rendering request (component name, props, and JavaScript bundle reference) to the Node Renderer over HTTP
  2. The Node Renderer evaluates the server bundle in a Node.js worker
  3. The rendered HTML is returned to Rails and inserted into the view
  4. Workers are pooled and can be automatically restarted to mitigate memory leaks

Key Features​

  • Worker pool — Configurable number of workers (defaults to CPU count minus 1)
  • Rolling restarts — Automatic worker recycling to prevent memory leak buildup
  • Bundle caching — Server bundles are cached on the Node side for fast re-renders
  • Shared secret authentication — Secure communication between Rails and Node
  • Prerender caching — Combined with prerender caching, rendering results are cached across requests

Getting Started​

Quick Setup (Generator)​

The fastest way to set up the Node Renderer is with the Pro generator:

bundle exec rails generate react_on_rails:pro

This creates the Node Renderer entry point, configures webpack, and adds the renderer to Procfile.dev.

Manual Setup​

For fine-grained control, see the Node Renderer installation section in the installation guide.

Configuration​

Configure Rails to use the Node Renderer:

# config/initializers/react_on_rails_pro.rb
ReactOnRailsPro.configure do |config|
  config.server_renderer = "NodeRenderer"
  config.renderer_url = ENV["REACT_RENDERER_URL"] || "http://localhost:3800"
  config.renderer_password = ENV.fetch("RENDERER_PASSWORD", "devPassword")
end

Further Reading​