How to get into the Rails console, or other tasks in a buildpack-based deploy

I’m running into the same problem as Elvinas.

Using /cnb/process/console does not work for me, the ssh session ends every time after a few seconds.

Oh I just replied to your other post. Sometimes Rails VMs crash with an out of memory error when they don’t have enough RAM and you run the console. That would end the session.

If you run fly status --all after this happens you might see a VM in a “failed” state. You can run fly vm status <id> on that one and it should tell you why it exited.

Thanks for your help, the following seems to be working for me :smiley: :

  • fly ssh console
  • launcher rails console
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When I run launcher rails console, I receive back /bin/sh: 1: launcher: not found

Is your app using a buildpack or a Dockerfile? You can tell from the [build] section of your fly.toml.

If it’s Rails 7, we generate a Dockerfile for it (buildpacks are for older Rails). Assuming that’s the case, you should be able to get Rails console by running:

-> fly ssh console

$ cd /app/
$ rails console

There may be a one liner for the SSH command, we’ll look!

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I’m running rails 7

I changed it to use 512mb of ram and I can access the console now!

I have 2GB on a staging machine and I can’t get any of this to work.

❯ fly ssh console -C "bash nohup ./process &" -a app
Connecting to complete
/usr/bin/nohup: /usr/bin/nohup: cannot execute binary file

Similar error for /cnb/process/console.

# launcher rails console
/bin/sh: 2: launcher: not found
# ./bin/rails console
Your Ruby version is 2.7.0, but your Gemfile specified 2.7.6

Still looking at other community topics to find what I am missing, I used turboku to bootstrap this app, so something must be different.

Try running fly ssh console -C "/bin/bash". Then run ls -la /cnb/process. Does it show anything?

You may need to run something like /lnb/launcher rails console.

 fly ssh console -C "/bin/bash" -a app-name
Connecting to top1.nearest.of.<app-name>.internal... complete
root@96186c8f:/# ls -la /cnb/process
ls: cannot access '/cnb/process': No such file or directory
root@96186c8f:/# /lnb/launcher rails console
bash: /lnb/launcher: No such file or directory
root@96186c8f:/# /cnb/launcher rails console
bash: /cnb/launcher: No such file or directory

I might be in a new architecture or something because I’ve never seen the cnb dir:

root@96186c8f:/# ls
app/    bin/    boot/   dev/    etc/    .fly/   home/   lib/    lib32/  
lib64/  libx32/ media/  mnt/    opt/    proc/   root/   run/    sbin/   
srv/    sys/    tmp/    usr/    var/
root@96186c8f:/# find . | grep launcher
root@96186c8f:/# find . | grep cnb
# no output

I’m running into this very same issue.

Apparently this is due to using multiple buildpacks.

Here is the list of my buildpacks in case that helps:

=== appname Buildpack URLs
1. heroku/metrics
3. heroku-community/apt
4. heroku/ruby

The 3rd one allows me to define apt dependencies, here is the Aptfile:


I added them mostly to be able to resize uploaded images.

I’m using pretty standard buildpacks:

  builder = "heroku/buildpacks:20"
  buildpacks = ["heroku/nodejs", "heroku/ruby"]

So I was able to get this working by:

fly ssh console
cd /app
cat profile.d/ # executing is denied

Exporting the variables found there manually sets up what we need. Then we can do bin/rails c and the console loads.

Update: My solution no longer works as now /app/profile.d no longer exists. For a few minutes on one deploy (currently working through another issue) /cnb/process existed but then disappeared when deploying again.

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I was able to get it working by doing:

fly ssh console
cd /app
bin/rails c

Hope this helps someone.

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Once I cleared up (admittedly many) other issues this seemed to go away, so I don’t have the solution as everything I did wasn’t related to this issue.