postCreateCommand in image

[Chuxel]

From @stephenandary

Hello :). I am wondering about a use case where I can build and push a devcontainer including post create commands so that a developer just needs to reference the built image. Some post create commands take very long and it would be nice to just build when updating for people. I tried to do this but when I referenced the image, it ran all of the build again. Wondering if doing this is possible (maybe I did something wrong).

Github Action Workflow Used: https://github.com/stephenandary/Dev_Containers/blob/main/.github/workflows/Rust-Dev_image_release.yml#L1-L30

[Chuxel]

postCreateCommand happens after the container has been created. As a result, its contents cannot be added to an image. Its intended to perform steps that requires the source code to be present to execute. A classic example is yarn install.

However, if this is your postCreateCommand, then it looks like all of those contents can be executed w/o the source code, so there's two options.

Add to a Dockerfile

You can add many of these commands to your Dockerfile. You can add it as follows:

COPY ./scripts/postCreateCommand.sh /tmp
RUN bash /tmp/postCreateCommand.sh && rm -f /tmp/postCreateCommand.sh

Or to run as a user other than root:

COPY ./scripts/postCreateCommand.sh /tmp
USER vscode
RUN bash /tmp/postCreateCommand.sh && rm -f /tmp/postCreateCommand.sh

A gotcha is that sometimes things require a login or interactive shell to work properly. Just add -li after bash to get one. You'll get a warning you can ignore about input devices, but otherwise it's fine to do.

COPY ./scripts/postCreateCommand.sh /tmp
USER vscode
RUN bash -li /tmp/postCreateCommand.sh && rm -f /tmp/postCreateCommand.sh

Use a local feature

However, if you want to run commands that depend on a specific Dev Container Feature, you can use a local feature. All Dev Container Features capabilities are available in local features, you just don't have to publish them if you don't want to. Here's how to convert that script into a local feature:

1. Create .devcontainer/local-feature

2. Add devcontainer-feature.json into the folder with the following contents:

   {
       "id": "local-feature",
       "version": "0.0.1",
       "installsAfter": ["ghcr.io/devcontainers/features/rust"]
   }

   The installsAfter is because the script uses cargo. If preferred you can just override the install order in devcontainer.json.

3. Now if you can run everything as root, you could just rename postCreateCommand.sh to install.sh and place it in .devcontainer/local-feature.

   [OPTIONAL] However, if you need to run as the non-root user (remoteUser) like postCreateCommand does, you can take advantage of the _REMOTE_USER environment variable with su. For example:

   1. Move postCreateCommand.sh to .devcontainer/local-feature
   2. Create install.sh in the same spot with the following contents:

      #!/bin/bash
      chmod 777 ./postCreateCommand.sh
      su ${_REMOTE_USER} -c 'bash postCreateCommand.sh'

      You can also use bash -li here as needed.

4. Add the reference under features in devcontainer.json:

   {
       //...
       "features": {
   	//..
   	"./local-feature": {}
   },
       //...
   }

That help?

[andar1an]

This is amazing, thank you so much for the response. I ran the script as a post-create command due to ownership issues, and it would have been a lot of work to figure out where I needed to take ownership of directories as not root post-build. So I will be able to avoid ownership issues for non-root by defining the users prior to running the script?! That is so cool, thank you so much again!

[Chuxel]

Glad it helped! @bamurtaugh raised a tracking issue for the kinds of "how-tos" should get added to containers.devs site (and probably the spec repo), so thanks for raising it! devcontainers/spec#137

[andar1an]

Very glad to learn about that site. In my experience with dev containers, I usually reference microsoft docs, and the containers are not always the most efficient, or concise. This can make them read a bit hacky. It will be really nice to see some how-to's with good examples! Really excited to try out what you mentioned above this weekend with my gh action. Im a big believer in giving people a consistent build environment with minimal set up required for each project. This project is awesome for potentially managing all of my different devcontainer builds from a single repo! <3

[andar1an]

@Chuxel, within devcontainer-feature.json, how do you put multiple features? I tried:

{
    "id": "local-feature-1",
    "version": "0.0.1",
    "installsAfter": ["ghcr.io/devcontainers/features/something"]
},
{
    "id": "local-feature-2",
    "version": "0.0.1",
    "installsAfter": ["ghcr.io/devcontainers/features/somethingelse"]
}

and variations on:

{
    "id": "local-feature-1",
    "version": "0.0.1",
    "installsAfter": ["ghcr.io/devcontainers/features/something"],
    
    "id": "local-feature-2",
    "version": "0.0.1",
    "installsAfter": ["ghcr.io/devcontainers/features/somethingelse"]
}

[andar1an]

@Chuxel As a note the reason I needed to install rust as vscode user was due to the following error if not using devcontainer as root:
warning: spurious network error (2 tries remaining): failed to create temporary file '/usr/local/cargo/registry/index/github.com-1ecc6299db9ec823/.git/objects/pack/pack_git2_80e6e668392a3819': Permission denied; class=Os (2)

Is it possible to install a feature as remote user?

[Chuxel]

For the first issue, you may need to chown first since I think root is the owner, and permissions are 700. So only root can access it.

chmod o+r your-filename-here

Also, FYI, there's a rust Feature now too (ghcr.io/devcontainers/features/rust) if you want to see how it works: https://github.com/devcontainers/features/tree/main/src/rust

@chrmarti @joshspicer I know this was set to 700 for caching purposes, but we could set this to be readable by everyone. Not sure there's value in being this restrictive. Thoughts?

[andar1an]

Thanks so much. I am trying to use the Rust feature. The reason I have avoided it in the past is the same issue I am experiencing now. It has been much easier for me to just install Rust. I moved the Rust question to https://github.com/orgs/devcontainers/discussions/13 so I don't overload this.

[andar1an]

@Chuxel I have tried taking ownership and changing file permissions at least 10 different ways. Still not able to reference the file from install.sh

[andar1an]

This seemed to do it:

chmod 777 -R $PWD
su ${_REMOTE_USER} -c './filename.sh'