Rails assets on MS Azure CDN

azure.rake

require 'azure_blob_service'

namespace :azure do

  desc 'Uploads application assets to Azure'
  task upload_assets: :environment do
    service = AzureBlobService.new(
      Rails.application.secrets.azure['account_name'],
      Rails.application.secrets.azure['access_key'])
    service.ensure_container_exists('assets')
    Dir.glob("#{Rails.root}/public/assets/**/*").each do |file|
      if File.file?(file)
        filename = file.gsub("#{Rails.root}/public/assets/", '')
        unless service.blob_exists?('assets', filename)
          Rails.logger.info("Uploading to Azure: #{filename}")
          service.upload_blob('assets', file, filename)
        end
      end
    end
  end

end

azure_blob_service.rb

require 'azure'

class AzureBlobService

  def initialize(account_name, access_key)
    Azure.configure do |config|
      config.storage_account_name = account_name
      config.storage_access_key   = access_key
    end
    @service = Azure::BlobService.new
    setup_cors
  end

  def upload_blob(container, file, filename)
    content = File.open(file, 'rb') { |file| file.read }
    content_type = MIME::Types.of(file).try(:first).try(:content_type)
    hash = Digest::MD5.base64digest(content)
    @service.create_block_blob(container, filename, content,
                               content_type: content_type,
                               content_md5: hash,
                               cache_control: 'public, max-age=604800')
  end

  def ensure_container_exists(name)
    unless @service.list_containers.any? { |c| c.name == name }
      @service.create_container(name, public_access_level: 'blob')
    end
  end

  def blob_exists?(container, name)
    begin
      @service.get_blob_properties(container, name)
      return true
    rescue Azure::Core::Http::HTTPError => err
      if err.status_code == 404
        return false
      else
        raise err
      end
    end
  end

  def setup_cors
    props = @service.get_service_properties
    return unless props.cors.cors_rules.empty?
    rule = Azure::Service::CorsRule.new
    rule.allowed_origins = cors_origins_for(Rails.application.secrets.domain_name, %w(app staging www))
    rule.allowed_headers = rule.exposed_headers = ['*']
    rule.max_age_in_seconds = 3600
    rule.allowed_methods = %w(GET HEAD)
    props.cors.cors_rules << rule
    @service.set_service_properties(props)
  end

  private

  def cors_origins_for(domain, subdomains, protocols = %w(http https))
    protocols.map do |proto|
      ["#{proto}://#{domain}"] + subdomains.map { |subdomain| "#{proto}://#{subdomain}.#{domain}" }
    end.flatten
  end
end

azure_capistrano.rb

namespace :deploy do
  task :upload_assets do
    on roles(fetch(:assets_roles)).first do
      within release_path do
        execute :rake, 'azure:upload_assets'
      end
    end
  end

  after 'deploy:assets:precompile', :upload_assets
end