Distillery to Releases

OTP25 was released a couple of weeks ago bringing JIT support to ARM (aka Apple M1). However, Distillery does not support OTP25. And I doubt it ever will given that it’s been all but replaced by Releases.

Distillery had a good run. But now it’s time to move on to releases.

This is a guide to help migrate from Distillery to Releases for Phoenix Applications built as Docker images running on Kubernetes with clustering provided by Libcluster.

(This is a specific case because you need the POD_IP set as part of the name in vm.args in order to cluster the nodes.)

Here’s a quick overview of the changes:

  1. Update mix.exs to remove Distillery
  2. Remove the Distillery related files
  3. Add new vm.args as /rel/vm.args.exs
  4. Generate the release configuration
  5. Update your configuration to load in the ENV
  6. Update your Dockerfile

Upon deploying the application you should be able to access the remote console using:

./bin/app remote

1. Update mix.exs to remove Distillery

Remove the following lines from mix.exs:

      # Distillery
      {:distillery, "~> 2.1"},
      # Config Providers
      {:config_tuples, "~> 0.4"},

Remove the following files and directories:


3. Add new the old vm.args configuration in /rel/env.sh.eex

You can generate this file using: mix release.init (which is separate from the phoenix command that you will run in the next step).

The following is my env.sh.eex file:

# rel/env.sh.eex
export RELEASE_NODE="app@${POD_IP}"

Note that you will need to replace the app name with the name of your otp app. And you can directly set the cookie. And RELEASE_DISTRIBUTION is NOT OPTIONAL. (I messed that part up for a while and was quite confused.)

4. Generate the release configuration.

Run mix phx.gen.release to generate the files needed to build the release.

This will generate files in /rel/overlays/bin needed to start the server and run migrations.

You will probably want to update lib/wildcast/release.ex to change the behaviour of the load_app function:

   defp load_app do

so that you don’t have errors with extra_applications such as ssl when running the migrations.

5. Update your configuration to load in the ENV

The default config provider in Distillery allows you to load in the ENV from special strings that are formatted like: "${ENV_VAR}".

This are replaced with the ENV variables at runtime.

Instead you will need to do move ALL RUNTIME config to a file called releases.exs and load in the ENV VARS using either System.fetch_env!/1 or System.get_env/2.

Use System.fetch_env!/1 when you want the app to crash if the proper ENV is not set.

Use System.get_env/2 when you want to use a default value if the ENV is not set OR if you want to allow nil for certain settings.

For example:

config :app, App.Repo,
   url: System.fetch_env!("DATABASE_URL"),
   pool_size: String.to_integer(System.get_env("DATABASE_POOL_SIZE", "20"))

requires that DATABASE_URL is set in the ENV but allows DATABASE_POOL_SIZE to be nil.

6. Update your Dockerfile

Finally, update your Dockerfile to use the the OTP25 images and to trigger migrations before starting the server.

You can also remove REPLACE_OS_VARS from the dockerfile if you were setting it there.

FROM elixir:1.13-otp-25-alpine as build
RUN MIX_ENV=prod mix release
FROM erlang:25-alpine
CMD ["sh", "-c", "/opt/app/bin/migrate && /opt/app/bin/app start"]

Mark Madsen

When I started writing Apps and APIs, phones had buttons!

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