Subdomains to restrict from your SaaS app

Many SaaS apps allow users to host their websites under their root domain, e.g. GitHub allows you to host your sites using GitHub Pages under the .github.io domain.

Here is a list of subdomains which you should reserve while building your own SaaS product.

I usually put this data in a /data/reserved_subdomains file and then use it like below:

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class Site < ActiveRecord::Base

  #...

  # validations
  SUBDOMAIN_RX = /\A[a-z\d]+(-[a-z\d]+)*\Z/i
  validates :subdomain, presence: true,
    uniqueness: true,
    length: { in: 4..63 , unless: Proc.new{ user && user.admin? }},
    format: {:with => SUBDOMAIN_RX},
    exclusion: { in: File.read(Rails.root.join("./data/reserved_subdomains")).each_line.map{|x| x.strip} , unless: Proc.new{ user && user.admin? }}

  #...

end
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