Hot code upgrades do not start porcelain

[NilsLattek]

I am using https://github.com/gutschilla/elixir-pdf-generator which depends on porcelain.
Elixir: 1.4
Erlang: 19
Porcelain: 2.0.3

Everything works fine, but when I do a hot code upgrade using releases with distillery, I can get error when call the pdf/porcelain code after the upgrade:

Ranch listener MyApp.Endpoint.HTTP had connection process started with :cowboy_protocol:start_link/4 at #PID<0.24063.0> exit with reason: 
{{%Porcelain.UsageError{message: "Looks like the :porcelain app is not running. Make sure you've added :porcelain to the list of applications in your mix.exs."}, 
[{Porcelain, :driver, 0, [file: 'lib/porcelain.ex', line: 419]}, 
 {Porcelain, :"-exec/3-fun-0-", 3, [file: 'lib/porcelain.ex', line: 131]}, 
 {Porcelain, :catch_throws, 1, [file: 'lib/porcelain.ex', line: 273]}, 
 {PdfGenerator, :generate, 2, [file: 'lib/pdf_generator.ex', line: 136]}, 
 {PdfGenerator, :generate_binary, 2, [file: 'lib/pdf_generator.ex', line: 188]}, 
 ...
]}, 
{MyApp.Endpoint, :call, [
  %Plug.Conn{ ... }}

When I restart my application/release it works again. So this currently prevents me from using hot code upgrades. Everything else works after the upgrade.
Porcelain is added in the mix.exs file:

def application do
    [mod: {MyApp, []},
     extra_applications: [
       :logger,
       :runtime_tools,
       :misc_random,
       :porcelain
      ]
    ]
  end

I also tried to add it to the distillery release config, without a difference.
Any ideas? Is it better to post this on pdf_generator or distillery issue tracker?

[Preen]

Any news on this?!

[samginn]

I'm experiencing the same error. Any updates on workarounds?

[darksheik]

It looks like the Supervisor does survive the hot upgrade, but it is not calling:

Porcelain.Init.init()

Doing this sets:

Application.fetch_env(:porcelain, :driver_internal)

If this environment variable is not set, you will see the error message that the app is not running.

[darksheik]

I made a little workaround for this which waits a bit after a config change before trying to reinit Porcelain. There may be a more elegant way to do this.

  defp ensure_porcelain_init() do
    Task.async(fn ->
      # Wait ten seconds after deploy and then try to reinit porcelain
      :timer.sleep(10000)
      Porcelain.Init.init()
    end)
  end

  # Tell Phoenix to update the endpoint configuration
  # whenever the application is updated.
  def config_change(changed, _new, removed) do
    ...
    ensure_porcelain_init()
    :ok
  end