We have several demo/example/tutorial Apps deployed to Heroku.
Apps on the "free" tier go to sleep after 30 minutes of inactivity.
see: https://devcenter.heroku.com/articles/free-dyno-hours

In order to wake them, we wrote a few lines of code that can be added to any Elixir/Phoenix App and invoked as an image in the README.md of the project that links to the App. So the app is ready to go by the time the person reading the README.md clicks on the link. 🔗

We had implemented the "wake from sleep" endpoint several times in our Heroku Apps, most recently in our email app. After copy-pasting the code a couple of times, we decided to make it a DRY reusable package that we can use in our next app(s)!

An easy way for us to wake our Heroku demo apps.

Note: our use case for this module is "just in time" waking of Heroku dynos.
If you need your "Free" Heroku app to be always awake or awake during specific times of day, consider combining the ping package with a CRON job. You can use a free service such as: https://cron-job.org as described by Mahdhi Rezvi in: https://medium.com/better-programming/keeping-my-heroku-app-alive-b19f3a8c3a82

This package is for anyone building an Elixir/Phoenix app deployed to Heroku.

Add ping to your Phoenix App and use it to wake your Heroku App in 4 easy steps:

Install by adding ping to your list of dependencies in mix.exs:

def deps do
  [
    {:ping, "~> 1.1.0"},
  ]
end

e.g: mix.exs#L61

Open the router.ex file of your Phoenix project and add the following route to your default pipeline:

get "/ping", PingController, :ping

e.g: lib/app_web/router.ex#L21

defmodule AppWeb.PingController do
  use AppWeb, :controller

  # see: github.com/dwyl/ping
  def ping(conn, params) do
    Ping.render_pixel(conn, params)
  end
end

e.g: lib/app_web/controllers/ping_controller.ex#L5-L7

You can either create a brand new controller, or use an existing one if you prefer.
We've created a new controller for clarity/separation.

Create the corresponding test file to keep your Test coverage complete:

defmodule AppWeb.PingControllerTest do
  use AppWeb.ConnCase

  test "GET /ping (GIF) renders 1x1 pixel", %{conn: conn} do
    conn = get(conn, Routes.ping_path(conn, :ping))
    assert conn.status == 200
    assert conn.state == :sent
    assert conn.resp_body =~ <<71, 73, 70, 56, 57>>
  end
end

e.g: test/app_web/controllers/ping_controller_test.exs#L5-L10

Add an image linking to the endpoint of the App to the README.md file:

![wake-sleeping-heroku-app](https://phxtodo.herokuapp.com/ping)

e.g: pull/5/files

The GIF is a transparent 1x1 pixel, so it's both minimal in size to minimise response time and invisible to the person. The idea is just to make the most basic HTTP request to the Heroku app in order to wake it. We don't actually care what is returned. But we don't want it to 404 so the person reading the README.md doesn't see an error in their console/browser.

Docs available at https://hexdocs.pm/ping. But there's really not much to it.