A Rails before_action to request bots retry-after X seconds when normalised load is high

bot_shedding.rb

def bot_shedding(wait: 600, threshold: 1)
  require "sys/cpu"
  require "etc"

  # normalize the 1-minute load average based on processor count
  return unless Sys::CPU.load_avg[0] / Etc.nprocessors > threshold
  return unless DeviceDetector.new(request.user_agent).bot?

  logger.info("Shedding bots: Returning 503 / Retry-After: #{wait} for #{request.remote_ip} / #{request.user_agent}")

  response.headers["Retry-After"] = wait.to_s # Ask clients to retry after X seconds
  render plain: "service unavailable: Retry in #{wait}", status: :service_unavailable
end