Hey folks, I am a newer of elixir, but I recently got a urgent demand。It
need forward the websocket request from the cowboy sever (http://127.0.0.1/api) to another server (http://127.0.0.1:8080/abc). In short， how to implement reverse proxy websockets using Cowboy.
The following is the framework I used:
cowboy: 2.9.0
plug_cowboy: 2.6.0
plug: 1.14.0

The following is my simple code:

# application.ex
defmodule Example.Application do
  use Application
  require Logger

  def start(_type, _args) do
    children = [
      {Plug.Cowboy, scheme: :http, plug: Example.Router, options: [port: 4000]}
    ]
    opts = [strategy: :one_for_one, name: Example.Supervisor]

    Logger.info("Starting application...")

    Supervisor.start_link(children, opts)
  end
end

# router.ex
defmodule Example.Router do
  use Plug.Router

  plug :match
  plug :dispatch

  get "/" do
    send_resp(conn, 200, "Welcome")
  end

  get "/start" do
    send_resp(conn, 200, "here is start page!")
  end

  get "/hello" do
    send_resp(conn, 200, "hello world!")
  end

  get "/api" do
    send_resp(conn, 200, "need to upforward websocket request to http://127.0.0.1:8080")
  end

  match _ do
    send_resp(conn, 404, "Oops!")
  end
end

The resposity of the project is GitHub - hrzyang/elixir_plug_cowboy_example: study elixir web framework plug_cowboy

hope you can help me, thanks very much !