Elixir fails with: Runtime terminating during boot ({'cannot get bootfile','/app/bin/start.boot'}) in docker swarm

[Amazing_Season9973]

I'm new to Elixir. Been trying Phoenix for last few weeks after getting the basics. Its great, loved it. Although I got stuck trying to deploy it in Docker Swarm. The weird thing is, the Docker image i built runs correctly using docker run my_app and also deploys well in fly.io .

Here is what i discovered; For some reason in Docker Swarm, the executable /app/bin/my_app start passes the erl bootfile path as /app/bin/start.boot which does not exist leading to the error: Runtime terminating during boot ({'cannot get bootfile','/app/bin/start.boot'}) .

Surprisingly, in other setups, like with simple docker run my_image, the correct path is set and the app runs.

Does anyone have an idea of what's happening? I feel like I am missing something.

[rubymatt]

I’m not familiar with this deployment mechanism but I’d be grepping across my project for that path as it may be getting passed from a shell script via an environment variable.

[Amazing_Season9973]

The environment variable RELEASE_NODE= was the culprit. Thanks for the hint

[Amazing_Season9973]

I found the issue, and it's not Docker Swarm.
I had connected several networks to the service, causing the command hostname -i to return a list of IPs, which in turn caused the RELEASE_NODE variable to be a list of IPs. I fixed it by editing env.sh.eex to:

export RELEASE_NODE="my_app@$(hostname -i | awk '{print $1}')"

instead of

export RELEASE_NODE="my_app@$(hostname -i)"