Rails API-only app setup for React frontend

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                  module MyApp
  class Application < Rails::Application
    config.load_defaults 6.1

    # API-only mode
    config.api_only = true

    # CORS configuration
    config.middleware.insert_before 0, Rack::Cors do
      allow do
        origins_list = if Rails.env.production?
                         ENV['FRONTEND_URL']
                       else
                         'localhost:5173', 'localhost:3001', /127\.0\.0\.1:\d+/
                       end

        origins origins_list

        resource '/api/*',
                 headers: :any,
                 methods: [:get, :post, :put, :patch, :delete, :options, :head],
                 credentials: true,
                 expose: ['Authorization']
      end
    end
  end
end

                  class ApplicationController < ActionController::API
  include ActionController::Cookies

  before_action :set_default_format

  private

  def set_default_format
    request.format = :json
  end
end

When building a React SPA, I configure Rails in API-only mode to skip view rendering, asset pipeline, and session cookies. The --api flag generates a lean Rails app focused on JSON responses. I enable CORS to allow the React dev server on localhost:5173 to communicate with Rails during development, while restricting origins in production. The rack-cors gem handles preflight OPTIONS requests automatically. I also configure Rails to use token-based authentication instead of session cookies since SPAs can't rely on same-origin cookie behavior. This setup provides a clean separation between backend API concerns and frontend presentation logic, making both easier to scale and deploy independently.

Maya Patel

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Rails API-only app setup for React frontend

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