Mix hangs when compiling code inside a Docker container

[jakubpawlowicz]

I've stumbled upon this issue when building a Docker container containing Erlang 17 + Elixir 1.0.4 + Phoenix 0.13.1. If you check out https://github.com/jakubpawlowicz/elixir-docker-issue and run docker-compose build then it hangs at step 15 - RUN mix compile:

Step 15 : RUN mix compile
 ---> Running in 6e4208f2275c
==> fs (compile)
Compiled src/fs_app.erl
Compiled src/fs.erl
Compiled src/fs_sup.erl
Compiled src/sys/inotifywait_win32.erl
Compiled src/sys/inotifywait.erl
Compiled src/sys/fsevents.erl
Compiled src/fs_event_bridge.erl
Compiled src/fs_server.erl

However it works fine when I attach to the container and run mix compile from CLI.

One workaround I found is to run mix compile with SMP turned off, see https://github.com/jakubpawlowicz/elixir-docker-issue/blob/master/Dockerfile#L29:

elixir --erl "-smp disable" /usr/local/elixir/bin/mix compile

My setup:

• OS X 10.10
• VirtualBox 4.3.26
• Boot2Docker 1.6
• docker-compose 1.2

Couldn't verify using Elixir master as I haven't figure out how to compile it inside Docker image yet.

I wonder if it's because mix compile uses Kernel.ParallelCompiler but then it does not explain why it works fine from CLI. Could be an issue with Docker not playing well with parallel commands?
Any further ideas?

[josevalim]

Maybe you can elixir -e "IO.inspect :erlang.system_info :schedulers_online" on both cases and print the result. There is nothing special about the parallel compiler, so i am really suspicious about what could be happening here.

[josevalim]

Also, I have heard reports of people running Elixir with Docker without any issues.

[jakubpawlowicz]

Thanks @josevalim. It gives 4 (in CLI and Dockerfile) and 1 when I disable SMP.

I kinda wondered why no one raised it before, but though it would be helpful to someone.
I'll try other combinations to rule out some options.

[josevalim]

@jakubpawlowicz any news here? All signs point this is not a bug in Elixir per se. Just in the mailing list someone posted a working docker setup with a phoenix app.

[jakubpawlowicz]

@josevalim I've retested it with centos:6 - no difference, but the setup posted by Saša Jurić at https://groups.google.com/forum/#!searchin/elixir-lang-talk/docker/elixir-lang-talk/IEcAtb9XHlU/mHx9A0Xx1_gJ works fine however it's based on Ubuntu not CentOS.

I think I'll close it for now, maybe someone would be able to add their 0.02$, otherwise we always have a working workaround.

[stevegraham]

+1 mix hangs for me too inside a docker container when started with docker run. I can docker exec to a running container no problem.

[sporto]

I'm having the same issue with docker compose, Docker just hangs on RUN mix do compile

Boot2Docker-cli version: v1.7.1
Docker version 1.7.1
docker-compose version: 1.3.1

I'm using this base image https://registry.hub.docker.com/u/marcelocg/phoenix/dockerfile/

[jakubpawlowicz]

I still stick to the workaround above.

[michaldarda]

I can confirm that this issue happens when using CentOS7, everything works on ubuntu

[stevegraham]

Great workaround @jakubpawlowicz. Works like a charm.

[simonewebdesign]

We had a similar issue, and the solution was to upgrade Elixir to the latest stable version (v1.1.1).

[eidge]

Having the same hanging issue with compile on elixir v 1.1.1 with ubuntu 14.04 both the image and the host os.

[josevalim]

Can you run elixir -e "IO.inspect :erlang.system_info :schedulers_online" and let us know what it returns? Can you reproduce it consistently in every repo or does it happen only in some particular applications?

[eidge]

It's my first application, haven't tried any other. Out of phoenix.new I get the compiler to hang.

> elixir -e "IO.inspect :erlang.system_info :schedulers_online"
** (UndefinedFunctionError) undefined function: IO.inspect/0
    (elixir) IO.inspect()
    (stdlib) erl_eval.erl:669: :erl_eval.do_apply/6
    (elixir) lib/code.ex:168: Code.eval_string/3