Start rails using dynamic ngrok host name

README.md

1. Get ngrok https://ngrok.com/download
2. Start ngrok ngrok http 3000
3. In a separate terminal, in your rails directory:

• copy ngrok-host script above to bin/ directory (drop the .rb, its just there for gist syntax highlighting.
• make the file executable: chmod +x bin/ngrok-host
• run: bin/ngrok-host

The script queries the local ngrok instance for available tunnels, grabs the https host name, and starts rails with that hostname configured for url helpers and the like.

But why?

Ngrok is a really useful tool for allowing access to a development server over a public URL with TLS encryption. I specifically needed this for testing an Android react-native client against a rails API.

The problem: starting and stopping Ngrok on a free account rotates and I got tired of copy-pasting the ever-changing hostnames into my rails config when I needed to restart.

development.rb

# frozen_string_literal: true

# Update config/environments/development.rb as follows:

Rails.application.configure do
  
   ...

  routes.default_url_options[:host] = ENV.fetch('HOSTNAME', 'localhost:3000')
end

ngrok-host.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

# this lives in bin/ngrok-host without the ".rb" extension

require 'httparty'

# Start rails server using temporary ngrok url for host names for urls (testing deep linking)

ATTEMPT_LIMIT = 5
attempts = 0
ngrok_host = nil

while ngrok_host.nil? && attempts < ATTEMPT_LIMIT
  begin
    response = HTTParty.get('http://127.0.0.1:4040/api/tunnels')

    https_tunnel = response.parsed_response['tunnels'].find { |t| t['proto'] == 'https' }

    ngrok_host = https_tunnel['public_url']
  rescue StandardError => e
    p e
    puts "Host not ready, retrying... #{ATTEMPT_LIMIT - attempts} tries left"
    attempts += 1
    sleep 1
  end
end

if ngrok_host
  puts "NGROK Host Found, starting rails"
  hostname = URI.parse(ngrok_host).host
  exec("HOSTNAME=#{hostname} bundle exec rails s")
else
  puts 'Unable to find ngrok host'
end