Codium Devcontainer

Alternative to proprietary VS Code Dev Containers for VSCodium, Positron, and similar IDEs. Uses Docker + SSH to build/run a container and open your folder inside it.

Features

• Open Folder in Devcontainer (SSH): Builds an SSH-enabled image, runs or reuses the container, configures keys, and opens the folder via Remote SSH.
• Rebuild & Open: Prompts to stop/recreate safely when the container is running.

Installation

• From Open VSX Marketplace (recommended for VSCodium/Positron/Theia):
  • UI: Extensions view → search for "Codium Devcontainer" → Install
  • CLI:
    • VSCodium: codium --install-extension DDorch.codium-devcontainer
    • Positron: positron --install-extension DDorch.codium-devcontainer
  • Open VSX page: https://open-vsx.org/extension/DDorch/codium-devcontainer
• From GitHub Releases (for VS Code or offline):
  • Download the latest .vsix from https://github.com/DDorch/codium-devcontainer/releases/latest
  • Install the VSIX:
    • VS Code: code --install-extension ./codium-devcontainer-X.Y.Z.vsix
    • VSCodium/Positron: codium|positron --install-extension ./codium-devcontainer-X.Y.Z.vsix
    • UI: Extensions view → “…” menu → Install from VSIX…

Prerequisites

• Docker installed and daemon running.
• A local SSH public key available (e.g., ~/.ssh/id_ed25519.pub or ~/.ssh/id_rsa.pub).
• Open Remote - SSH extension installed

Quickstart

1. Create a devcontainer config:

{
  "image": "mcr.microsoft.com/devcontainers/javascript-node:22"
}

2. Use the Command Palette or status bar:

• Devcontainer: Open Folder in Devcontainer (SSH)
• Devcontainer: Rebuild & Open
• Click the status bar “Devcontainer” item for quick actions.

Supported devcontainer.json

• image: Base image used as BASE_IMAGE for the build.
• remoteUser: Effective/SSH user inside the container. Optional; auto-detected if omitted.
• postCreateCommand: String or array. Injected as Dockerfile RUN steps during image build.
• postStartCommand: String or array. Executed in a terminal when each remote session starts.

How it Works

• Build Phase:
  • Generates a temporary Dockerfile from the template, sets BASE_IMAGE to your image, and appends postCreateCommand as RUN steps.
  • Stages a small entrypoint that starts sshd, builds the image, then removes the staged and temporary files.
• Run Phase:
  • Starts the container, bind-mounts your folder to /workspace/<folder>, sets the working directory, and exposes SSH on a random localhost port.
  • Adds your SSH public key and chooses the effective user (remoteUser if provided, otherwise auto-detected).
• Open Workspace:
  • Creates an SSH host alias and opens the folder inside the container over Remote SSH.
• Lifecycle:
  • Reuses the per‑project container when possible; if .devcontainer/devcontainer.json changed since creation, prompts you to rebuild.
  • Runs postStartCommand in a terminal when each remote session starts.
  • Stops the container shortly after the session ends.

Limitations

• Debian/Ubuntu images recommended (template installs openssh-server via apt).
• Single container only; dockerComposeFile and multi-service setups are not supported.
• Build settings in devcontainer.json are ignored: dockerFile, build, context, args, target, features are not read. The extension always builds from its template using image as the base.
• Runtime settings like mounts, runArgs, containerEnv, init, privileged, capAdd, securityOpt, forwardPorts/portsAttributes are not applied.
• Lifecycle commands other than the two listed are not supported: onCreateCommand, updateContentCommand, postAttachCommand are ignored.
• No authoring tools for devcontainer.json.
• One container per project name; the extension reuses it when possible.
• Docker volumes are not managed (bind mounts only).

Please open issues for feature requests for leveraging more devcontainer.json settings.

Testing Locally

See contributing guide for local testing instructions.

Commands

• Devcontainer: Add Dockerfile Template — creates .devcontainer/Dockerfile from the template.
• Devcontainer: Open Folder in Devcontainer (SSH) — builds with BASE_IMAGE, runs/reuses with SSH on a random local port, configures your key, and opens the folder over SSH.
• Devcontainer: Rebuild & Open — forces rebuild and safe recreate when needed.
• Devcontainer: Open Devcontainer Configuration — opens .devcontainer/devcontainer.json.
  • Note: Explorer context menu entries appear only when .devcontainer/devcontainer.json exists.

Troubleshooting

• SSH connection issues:
  • Firewalls or corporate endpoint protection can block localhost SSH connections; temporarily disable or add an allow rule if needed.
• Remote - SSH missing: the command will prompt to install it. If it isn't available in your marketplace, use "Devcontainer: Build & Run" and work via the opened SSH terminal, or manually connect with your preferred SSH client to <user>@localhost:<port> (the user is either remoteUser or detected via whoami).
• No public key found: you will be asked to select a *.pub key.
• Docker permissions: ensure your user can run Docker commands without sudo.

Contributing

Development setup, testing, packaging, and release instructions are in CONTRIBUTING.md.

Changelog

See NEWS.md for release notes.

License

This project is licensed under the MIT License.

See LICENSE for the full text.

Acknowledgements

This extension is inspired by Andrew Heiss’s blog post:

Heiss, Andrew. 2025. “Use Positron to Run R Inside a Docker Image Through SSH.” July 5, 2025. https://doi.org/10.59350/fredm-56671.