The Process that retries itself without monitor, supervisors.

hydra.ex

defmodule Hydra do
  use GenServer

  def run(data) do
    {:ok, pid}  = GenServer.start(__MODULE__, data, [])
    GenServer.cast(pid, :process)
  end

  def init(data) do
    {:ok, data}
  end

  def process(pid) do
    GenServer.cast(pid, :process)
  end

  def handle_cast(:process, {url, retry} = all) do
    if retry !== 0, do: IO.puts "Retrying... #{retry} time"
    url |> fetch_data |> save_data
    {:noreply, all}
  end

  def terminate(:normal, _), do: nil

  def terminate(:normal, {_url, 3}) do
    IO.puts "Tried 3 times. No luck :( "
  end
  
  def terminate(_, {url, retry}) do
    run({url, retry + 1})
  end

  defp fetch_data(url) do
    IO.puts "Requesting API for #{url}"
    1/0
    "data"
  end

  defp save_data(data) do
    IO.puts "Storing the data to remote database: #{data}"
    Process.exit(self, :normal)
  end
end
Hydra.run({"/api/users", 0})
Hydra.run({"/api/posts", 0})
Hydra.run({"/api/comments", 0})