Rate Limit na volani externiho API

rate_limit.md

Rate Limit na volani externiho API

Nekdy potrebujete nepretizit externi API svymi pozadavky. Podivame se na jednoduchy zpusob, jak to provest pomoci knihovny jobs od Ulf Wiggera.

Externi API ma problem, kdyz mu posleme vic nez 5 pozadavku za vterinu. Takze potrebujeme omezit pocet volani na 5 za sekundu.

Zaroven chceme po obdrzeni odpovedi z API pokracovat tam, kde jsme prestali. Na to pouzijeme klasicky Beamovsky send & receive. Timto zpusobem muzeme API volat klidne z 50 jinych procesu a mame zaruceno, ze externi API nepretizime. Zaroven API vyuzivame na 100% jeho moznosti.

mix.exs

    {:jobs, "~> 0.10.0"}

application.ex

    :jobs.add_queue(:rate_limited_queue, [ {:regulators, [{ :rate, [{:limit, 5}]}]}])

nekde v kodu

  def rate_limited_action(params) do
    pid = self()
    :jobs.run(:rate_limited_queue, fn ->
      send(pid, {:queue_response, action(params)})
    end)
    receive do
      {:queue_response, result} ->
        result
      _ ->
        {:error, :unexpected_status_from_rate_limited_queue}
    after
      30_000 ->
        {:error, :timeout_of_from_rate_limited_queue}
    end
  end

Odkazy:

• Knihovna jobs: https://github.com/uwiger/jobs
• Algoritmy potrebne k implementaci Rate Limiteru: https://akoutmos.com/post/rate-limiting-with-genservers/
• Rate Limiting pomoci placene verze Obanu: https://hexdocs.pm/oban/2.11.0/smart_engine.html