Heroku app recompiles after restarts using Elixir 1.15

beerlington

I upgraded to Elixir 1.15 and am having issues deploying on Heroku now. Whenever the app restarts, the whole application recompiles. On our large application, this recompile takes longer than 30 seconds, which causes the app to crash.

I’m able to reproduce this on a bare bones Phoenix app. The line where it says “Compiling 15 files” should not be happening during a restart.

2023-07-06T14:42:59.587968+00:00 heroku[web.1]: Restarting
2023-07-06T14:42:59.650735+00:00 heroku[web.1]: State changed from up to starting
2023-07-06T14:43:00.295043+00:00 heroku[web.1]: Stopping all processes with SIGTERM
2023-07-06T14:43:00.322078+00:00 app[web.1]: 14:43:00.321 [notice] SIGTERM received - shutting down
2023-07-06T14:43:00.322086+00:00 app[web.1]: 
2023-07-06T14:43:01.502645+00:00 heroku[web.1]: Process exited with status 0
2023-07-06T14:43:03.720077+00:00 heroku[web.1]: Starting process with command `mix phx.server`
2023-07-06T14:43:05.363804+00:00 app[web.1]: Compiling 15 files (.ex)

Where should I report this issue? I don’t know if it’s something specific to Elixir or if the Heroku buildpack we’re using needs to be updated to support Elixir 1.15. GitHub - HashNuke/heroku-buildpack-elixir: Heroku Buildpack for Elixir with nitro boost · GitHub

7 comments

#deployment

1 1042 7

2025-08-15 17:05:50 UTC

Showing Posts 7 to 1

Show Best Posts
Show All (oldest first)
Show All (newest first)

iamyojimbo

I have posted an update here: Additional recompile occurring on Heroku with Elixir 1.15 causing boot issues · Issue #12771 · elixir-lang/elixir · GitHub

Read there for more detail. The root cause is that elixir 1.15 introduced cwd in the cache key after compilation. Heroku compiles code in a tmp build dir, but is run from /app.

Fix it by using your exact same Procfile as before, but passing in --no-compile, as detailed here: Changing absolute path of mix project causes full recompilation · Issue #13241 · elixir-lang/elixir · GitHub

So change your procfile to:

release: mix do ecto.migrate --no-compile, any_other_example_mix_command
web: MIX_ENV=prod mix phx.server --no-compile

You do not need to use releases.

Post #7

AlfredBaudisch

For those coming here with a setup similar to mine:

Elixir 1.15
OTP 26
Heroku
Phoenix 1.7
And Umbrella app (4 apps)

The solution to make it work with Heroku, as explained previously, is to migrate to use Releases, but then, Node and npm weren’t being run so statics assets were not being compiled (i.e. apps/xxx/assets).

In the end I made it work in Heroku by adding a Procfile manually, keeping the Elixir and Phoenix static assets buildpacks, adding an additional “elixir mix release” buildpack and setting Phoenix Endpoint as a server.

Configuration step by step:

Phoenix Endpoint

I had a lot of trouble making Phoenix start in Heroku when building the mix release. In the end, this is what I needed to put inside config/runtime.exs. The secret lies in adding server: true, otherwise the Elixir release won’t start Phoenix as a server and Heroku will timeout on startup.

if config_env() == :prod do
  config :fb_web, Farmbackup.Endpoint,
    http: [
      port: {:system, "PORT"},
      compress: true,
      timeout: 60_000,
      protocol_options: [
        idle_timeout: 60_000
      ]
    ],
    url: [scheme: "https", host: System.fetch_env!("FARMBACKUP_HOST"), port: 443],
    debug_errors: false,
    cache_static_manifest: "priv/static/cache_manifest.json",
    secret_key_base: System.fetch_env!("SECRET_KEY_BASE"),
    server: true
end

mix.exs release

In the main mix.exs file add all your umbrella apps in the releases config key:

  def project do
    [
      apps_path: "apps",
      start_permanent: Mix.env() == :prod,
      deps: deps(),
      aliases: aliases(),
      releases: [
        fb_task: [
          applications: [
            fb_web: :permanent,
            fb_db: :permanent,
            fb_invoice: :permanent,
            fb_salary: :permanent
          ],
          version: DateTime.utc_now() |> DateTime.to_iso8601()
        ]
      ]
    ]
  end

Heroku Buildpacks

You are going to need these 3 buildpacks installed in order:

https://github.com/HashNuke/heroku-buildpack-elixir.git
https://github.com/gigalixir/gigalixir-buildpack-phoenix-static
https://github.com/chrismcg/heroku-buildpack-elixir-mix-release

Buildpack config

elixir_buildpack.config

erlang_version=26.1.2
elixir_version=1.15.7
always_rebuild=false
runtime_path=/app

phoenix_static_buildpack.config

clean_cache=true
phoenix_relative_path=apps/fb_web (i.e. app in the umbrella which has `/assets`)
assets_path=apps/fb_web/assets
node_version=v14.15.5
npm_version=6.14.11

Procfile

YOU need to manually create a Heroku Procfile for Umbrellas.

In our case it is:

web: _build/prod/rel/fb_task/bin/fb_task start

Post #6

beerlington

That’s perfect. Thanks for your help!

Post #5

johantell

If you haven’t found it already: Deploying with Releases — Phoenix v1.8.8

Post #4

johantell

Yes, running the migrations through mix will force recompilation. There is a way around it though, i think its described quite well under the phoenix release docs. In short its a helper function that is called via the release through the eval command

Post #3

beerlington

Thanks for the suggestion. I was able to get our app running on Heroku with mix releases with minimal changes. One thing that seems a bit odd is that the app recompiles during Heroku’s release phase when we run migrations. It only does this in 1.15 and not 1.14, so it think there’s still something “off” here. The app at least starts up, but adds a few minutes to deploy time.

Post #2

johantell

Have you considered deploying elixir through mix releases on heroku? That should prevent having to recompile and also bring some other benefits.

It might not answer your question but i can recommend looking i to it as this problem will reoccur even if you manage to solve it for now . I would post links but I’m currently on my phone so i have limited resources. I will try to do so later

Post #1

— All posts loaded —