October 9, 2023

Use Subdomains Locally In Rails

To use subdomains locally in Rails, set the hosts explictly or update the top level domain length.

Routes file with the app. subdomain constraint:

# config/routes.rb
Rails.application.routes.draw do
  root "marketing#index"

  constraints subdomain: "app" do
    get "/", to: "posts#index"
  end
end

Option 1: Set hosts

# config/environments/development.rb
Rails.application.configure do
  config.hosts = ["app.example.localhost", "example.localhost"]
end

# Add hosts to your /etc/hosts file
127.0.0.1 app.example.localhost
127.0.0.1 example.localhost

Option 2: Update the top level domain length

# config/environments/development.rb
Rails.application.configure do
  config.action_dispatch.tld_length = 0
end

# Add hosts to your /etc/hosts file
127.0.0.1 app.localhost

Test Setup

minitest

# test/application_system_test_case.rb
require "test_helper"

class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
  def setup
    Capybara.app_host = "http://app.localhost"
  end

  driven_by :selenium_chrome_headless, using: :chrome, screen_size: [1400, 1400]
end

rspec

# This file is copied to spec/ when you run 'rails generate rspec:install'
require "spec_helper"
ENV["RAILS_ENV"] ||= "test"
require_relative "../config/environment"
require "rspec/rails"


Capybara.app_host = "http://app.localhost"

RSpec.configure do |config|
  # ...other config
end

To test another subdomain, set the Capybara.app_host before a test block.