A slightly more sophisticated Sinatra example for ember-cli-deploy

ember-cli-deploy-redis-sinatra.rb

require 'sinatra'
require 'redis'

configure do
  # Define your Redis connection, key prefix, and revision preview query parameter here!
  set :redis, Redis.new
  set :prefix, 'foo:index'
  set :param_key, 'preview'
end

helpers do
  def fetch_index
    stack = []

    stack.push params.fetch(settings.param_key, 'current')
    while value = settings.redis.get("#{settings.prefix}:#{stack.last}")
      return [value, stack.last] if value =~ /\s/
      break if stack.include? value # cycle guard
      stack.push value
    end

    not_found 'Invalid Site Index'
  end

  def extract_http_equiv!(content)
    modified_content = content.dup
    content.scan(/<\s*meta\s+http-equiv="?([\w-]+)"?\s+content="?(.+?)"?\s*>/im) do |pairs|
      yield pairs
      modified_content.slice! $&
    end
    content.replace modified_content
  end
end

get '/', :provides => :html do
  index, revision = fetch_index
  
  etag revision
  expires 3_600, :public
  extract_http_equiv!(index) do |key, value|
    response[key] = value
  end
  index.gsub(/\n */, '')
end

It's probably overkill, but this supports multiple levels of index indirection (e.g. staging => current => abcd1234) and ETags for cache control. Based off of the original. It also extracts http-equiv meta tags from the index content and presents them as HTTP response headers instead, which is useful for certain CSP options. See also ember-cli-deploy-mysql-sinatra.rb.