Run it via: CHAOS=100 ./chaos_server.exs

chaos_server.exs

#!/usr/bin/env elixir

# This is a small HTTP server that accepts requests and is designed to randomly
# fail, allowing other software to be tested for robustness.

Mix.install([
  {:bandit, "~> 0.6.8"},
  {:plug, "~> 1.14"}
])

defmodule ChaosServer do
  import Plug.Conn
  require Logger

  def init(opts) do
    opts
    |> Keyword.put_new(:chaos, 30)
    |> tap(fn opts ->
      Logger.info("ChaosServer will crash #{Keyword.fetch!(opts, :chaos)}% of the requests")
    end)
  end

  def call(conn, opts) do
    if crash?(opts) do
      raise RuntimeError
    else
      conn
      |> put_resp_content_type("text/plain")
      |> send_resp(200, "")
    end
  end

  defp crash?(opts) do
    Enum.random(1..100) <= Keyword.fetch!(opts, :chaos)
  end
end

Bandit.start_link(
  plug: {ChaosServer, chaos: String.to_integer(System.get_env("CHAOS", "30"))},
  options: [port: 4000]
)

Process.sleep(:infinity)