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Zil Norvilis
Zil Norvilis

Posted on • Originally published at norvilis.com

The Magic of lvh.me: Testing Rails Subdomains in Development

#rails #webdev #productivity #devops

The /etc/hosts Headache

If you are building a SaaS that uses subdomains (like app.mysite.com or tenant.mysite.com), testing them locally is usually a pain.

The traditional way is to edit your /etc/hosts file:

127.0.0.1  mysite.local
127.0.0.1  app.mysite.local
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This is tedious, requires sudo privileges, and you have to remember to do it for every new tenant or project.

There is a better way. It’s called lvh.me.

What is lvh.me?

lvh.me (Local Virtual Host) is a free service that simply points its DNS "A" record to 127.0.0.1.

Because it is a real registered domain name, it supports wildcards. This means:

  • lvh.me points to 127.0.0.1
  • app.lvh.me points to 127.0.0.1
  • any-thing-you-want.lvh.me points to 127.0.0.1

You don't have to install anything. You don't have to configure any DNS. It just works.

Step 1: The Rails Security Barrier

Since Rails 6, there is a security feature that blocks "Host Header Attacks." If you try to visit http://lvh.me:3000 right now, Rails will show you a "Blocked Host" error page.

You need to whitelist the domain in your development configuration:

# config/environments/development.rb

# Allow the main domain and all subdomains
config.hosts << ".lvh.me"
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Note the dot before lvh.me - this is the wildcard that allows any subdomain.

Step 2: Accessing your App

Restart your Rails server. Now, instead of localhost:3000, open your browser and go to:

http://lvh.me:3000

If you want to test your subdomain logic:

http://app.lvh.me:3000
http://blog.lvh.me:3000

Step 3: Handling Subdomains in Code

If you are using the routing constraints we discussed in the previous article, Rails will now correctly identify the subdomain.

You can test this in your controller:

class ApplicationController < ActionController::Base
  before_action :check_subdomain

  def check_subdomain
    puts "Current subdomain: #{request.subdomain}"
  end
end
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Step 4: Session & Cookie Sharing

If you need to stay logged in while moving between lvh.me and app.lvh.me, ensure your session store is configured to handle the domain correctly:

# config/initializers/session_store.rb
Rails.application.config.session_store :cookie_store, 
  key: '_your_app_session', 
  domain: :all,
  tld_length: 2 # This is important for lvh.me
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Why tld_length: 2?
Standard Rails assumes a TLD like .com or .org (length 1). Since lvh.me has two parts, you tell Rails to look two levels deep to find the "root" domain.

Bonus: SSL with Puma-dev

If your app requires HTTPS locally (for example, if you are testing Stripe webhooks or Secure Cookies), lvh.me might not be enough because it doesn't provide an SSL certificate for your local machine.

In that case, look into Puma-dev. It acts as a local DNS server and provides a self-signed SSL certificate for .test domains. But for 90% of development work, lvh.me is the fastest "zero-config" solution.

Summary

  1. Stop manually editing /etc/hosts.
  2. Add config.hosts << ".lvh.me" to your development config.
  3. Use any subdomain you want instantly.

Do you use lvh.me or do you prefer puma-dev? Share your local setup tips below! 👇

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