mix release is a really wonderful tool, but it doesn’t support hot code upgrades while Distillery does.

So if you want to use Distillery here are the steps that you need:

1. Use Erlang/OTP 24 because Distillery is not compatible with OTP 25

2. Use Elixir version 1.14 or earlier. If you use a later version, you will not be able to run the IEx console in Distillery release. I suppose the reason is here and after Elixir 1.14 module IEx.CLI was refactored

Here is my tool-versions file from the brilliant asdf version manager:

erlang 24.3.4.17
elixir 1.14.5

3. Create config/config.exs file with this content:

import Config

4. Also don’t forget to use appropriate elixir version in project function from the mix.exs file, for example:

  def project do
    [
      app: :sequence,
      version: "0.1.0",
      elixir: "~> 1.14",
      start_permanent: Mix.env() == :prod,
      deps: deps()
    ]
  end

Yes, I also read this wonderful book and encountered the same problem

5. Use mix task which starts from the distillery prefix, for example: mix distillery.init and mix distillery.release --env=prod (my Distillery version is 2.1.1)

With all this, I was able to successfully complete the entire chapter of the book.

Sometimes, this occurs just like it does with any other application in a different stack. However, it is usually common practice to use Docker and simply redeploy the container with the previous version.

I apologize; at first, I misunderstood the question.

It depends. we usually strive to use the latest versions of Elixir/Erlang. However, if it’s a critical system, there might be a compromise: using hot code updates but sticking to slightly older versions of Elixir/Erlang.

One way or another, I haven’t encountered the use of hot code updates in production. Typically, Docker containers are used along with the latest versions of Elixir/Erlang. Nevertheless, it was useful to get acquainted with this mechanism and experiment with it in the context of this chapter of the book.

While there‘s no built in support it can be added by third parties: Castle - Hot-Code Upgrade Support for Elixir