Add ELIXIR_ERL_OPTIONS to rel/env.sh.eex file

[derrickreimer]

The default env.sh.eex file generated by mix release.init does not include the ELIXIR_ERL_OPTIONS export:

https://github.com/elixir-lang/elixir/blob/7e4fbe657dbf9c3e19e3d2bd6c17cc6d724b4710/lib/mix/lib/mix/tasks/release.init.ex#L59-L78

However, it appears this line is necessary in order for Fly networking to work properly (see https://community.fly.io/t/could-not-contact-remote-node-reason-nodedown-aborting/5221/3?u=derrickreimer).

Relatedly, I was not able to successfully start an IEx session (following these instructions) until I made these updates to the env.sh.eex file. The instructions for changing env.sh.eex are listed below the IEx instructions, so it might be trip-up point if folks are following this guide sequentially. I would recommend moving this portion higher in the guide, but have refrained from doing so in this PR, since that's a bigger structural change.

Thanks all!

[brainlid]

Thanks @derrickreimer for reporting the issue! We'll check it out.

[brainlid]

Hi @derrickreimer!

I created a new Phoenix app (v1.6.10) and following the guide I had no problems.

I got an IEx shell to the newly deployed app.

I then went ahead and ran the mix release.init. After doing that and deploying I was still able to IEx into the node.

The ENV setting is appended to the Dockerfile by the flyctl program.

# Appended by flyctl
ENV ECTO_IPV6 true
ENV ERL_AFLAGS "-proto_dist inet6_tcp"

It sets it under a different key, but it works for me.

Are you working with a custom Dockerfile that doesn't have this setting or was your Phoenix app generated with an older version of Phoenix?

We used to have that setting in the documentation but IIRC, it was removed because it can cause problems in other scenarios? Not sure right now.

[derrickreimer]

Ah, interesting! I used the Dockerfile generated by mix phx.gen.release --docker and I'm not sure why those ENVs did not get appended when I deployed to Fly initially. I believe I had already created a fly.toml file, so perhaps those auto-scaffolding steps were skipped?

At any rate, I added those appends to my Dockerfile (and removed ELIXIR_ERL_OPTIONS from env.sh and it works! This might be enough of an edge case that documentation about it is not warranted, but could be helpful to include in a troubleshooting section somewhere for those who are retrofitting an existing Dockerfile.

Thanks for the help!

[brainlid]

Thanks for the follow-up! I agree that it should be included as a troubleshooting step if not elsewhere as well.

Thanks!

[brainlid]

@derrickreimer I updated the docs to hopefully help future devs who hit this issue.

You can checkout the update here:
https://fly.io/docs/getting-started/elixir/#important-ipv6-settings

Let me know if you feel it could be improved and how.

Thanks!

[derrickreimer]

That looks great!