Packer overrides CMD and ENTRYPOINT already set in FROM image about packer-plugin-docker HOT 14 CLOSED

@nywilken

any update on this?

it's a very fundamental feature that this plugin lacks

from packer-plugin-docker.

I've run into this issue and it's super unexpected. packer should definitely not clobber CMD/ENTRYPOINT if it's not defined in the packer script.

from packer-plugin-docker.

I mean that was my "workaround" too -- setting ENTRYPOINT everywhere back to some 'default'. This is not a solution.

from packer-plugin-docker.

Any update on this issue? I am facing the same problem. The official doc doesn't explain the current behavior.

from packer-plugin-docker.

Our development team is facing the same problem. Hope a fix can be made :)

from packer-plugin-docker.

To be more precise :
Here is the definition of the 'Cmd' and 'Entrypoint' fields on a base image pulled from DockerHub :

# docker inspect debian:bullseye-slim -f '{{ .ContainerConfig.Cmd }}
[/bin/sh -c #(nop)  CMD ["bash"]]
# docker inspect debian:bullseye-slim -f '{{ .ContainerConfig.Entrypoint }}
[]

When we build an image derived from this Debian base image with Packer, even if we only add a LABEL, the 'Cmd' and 'Entrypoint' fields are modified, which is not the case when using a Dockerfile :

# docker inspect <our_image> -f '{{ .ContainerConfig.Cmd }}
[]
# docker inspect <our_image> -f '{{ .ContainerConfig.Entrypoint }}
[/bin/sh]

Note : Extract from the Packer's template, which is very simple :

source "docker" "debian-bullseye" {
  image  = 'debian:bullseye-slim'
  commit = true
  changes = [
    "LABEL env=devel"
  ]
}

from packer-plugin-docker.

It seems that this problem can't be solved easily. The behavior comes from the way the Docker builder works : it is derived from the docker commit command, and Packer run the container with run_command which define the entrypoint to /bin/sh :

["-d", "-i", "-t", "--entrypoint=/bin/sh", "--", "{{.Image}}"]

That's the reason why the CMD and ENTRYPOINT are changed.
The Docker builder is a beautiful plugin but, unfortunately, not very usable.

from packer-plugin-docker.

Hi,
Maybe we can imagine a simple solution like this :
when a Docker image is build and do not define CMD nor ENTRYPOINT values, the Docker Plugin get this parameters from the base image (defined in the source.docker block) and automatically add them into the "changes" array, so that they would be taken into account by the docker commit --change command.

What do you think about it ?
Thanks.

from packer-plugin-docker.

Any effective workarounds?

from packer-plugin-docker.

yeah, just use another container builder

from packer-plugin-docker.

@dimisjim suggestions?

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https://github.com/docker/buildx

from packer-plugin-docker.

I think I figured out a workaround.

Instead of leaving ENTRYPOINT blank, I set ENTRYPOINT to a command that is effectively equivalent to nothing but that Packer won't clobber:

    "ENTRYPOINT [\"/bin/sh\", \"-c\", \"exec \\\"$0\\\" \\\"$@\\\"\"]",

Ugly but seems to work.

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@josh-m-sharpe you're right, it's not a solution. It's a workaround lol

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