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I created a Docker image and container via docker-compose that consists of a Rails app backed by PostgreSQL. Rails is meant to start via a docker-entrypoint.sh file which looks like this:

#!/bin/sh # Exit early if there are any errors. set -e # Check that there won't be any server conflicts. if [ -f tmp/pids/server.pid ]; then rm tmp/pids/server.pid fi # -b binds the server to all IP addresses, rather than to localhost. bundle exec rails s -b 0.0.0.0

However, the container stops immediately after startup with this error:

bundler: failed to load command: rails (/usr/local/bundle/bin/rails) LoadError: cannot load such file -- /usr/local/bundle/specifications/exe/rails /usr/local/bundle/bin/rails:23:in `load' /usr/local/bundle/bin/rails:23:in `<top (required)>'

Since to my knowledge you can't directly explore the filesystem of a stopped container, I exported the entire filesystem to a .tar file:

docker export a2410e604db9 > container.tar

Looking inside of container.tar, I found that there is a /usr/local/bundle/bin/rails executable file, so I don't know why bundle wouldn't be able to load that command.

The other directory that is mentioned in the error, /usr/local/bundle/specifications/exe/rails, does not exist. There is only /usr/local/bundle/specifications, which contains a bunch of .gemspec files for the Rails project and nothing else.

What is causing this bundler/LoadError problem?

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  • How are you running the container? If the image isn't configured to ignore it (the script you provide is run as the image's CMD, not its ENTRYPOINT) you can docker run --rm -it your-image bash to get an interactive shell on the image to poke around. Commented Sep 15, 2020 at 18:38
  • @DavidMaze I did know about the interactive shell, but my container stops right after it starts, so as far as I can tell, it's impossible to get an interactive shell. The script I provided above is run as an ENTRYPOINT, though, in my Dockerfile: ENTRYPOINT ["./entrypoints/docker-entrypoint.sh"]. Commented Sep 15, 2020 at 19:22
  • If you change that to CMD then you can override it at run time as shown above. You can also split the ENTRYPOINT and CMD; if you make the last line of the script exec bundle exec "$@" then whatever command you pass (default: CMD rails s -b 0.0.0.0) will get run in the Bundler context. Commented Sep 15, 2020 at 20:16
  • @DavidMaze Not sure I understand. I changed the last two lines of my Dockerfile to ENTRYPOINT ["./entrypoints/docker-entrypoint.sh"] and CMD rails s -b 0.0.0.0. I changed the last line of my entrypoint script to exec bundle exec "$@". The container still crashed immediately after start. I then ran docker run --rm -it 64e8e33e8fc1 bash, and the Rails server started right there in the console -- no interactive shell, which I thought was the goal -- but the Rails server is inaccessible in the browser, as though it wasn't running. I'm completely lost. Commented Sep 16, 2020 at 13:32
  • OK, I was able to get a shell by scrapping the attempt in my previous comment, and simply changing ENTRYPOINT to CMD, and nothing else. I could then run docker run --rm -it 93350aeeab9c sh to get a shell into the image that failed to start. So that's something. Commented Sep 16, 2020 at 17:15

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What docker image are you using for your rails app? If it's the public library/ruby one then I presume all the required env variables will be set correctly for your script to work.

I suggest sharing your Dockerfile if it isn't the public ruby one.

First see if your PATH (and script) are using the intended bundle and rails:

docker run -it <YOUR_DOCKER_IMAGE> bash which bundle which rails

If not, try running it manually first before scripting to diagnose issues:

docker run -it <YOUR_DOCKER_IMAGE> bash cd /path/to/app bundle exec rails s -b 0.0.0.0

Lastly, ensure your docker-compose.yml file exposes the port you're expecting. If it's 4000:

ports: - "4000:4000"
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