Dev Containers: Local Add-on

A small add-on for the Dev Containers VS Code extension that merges local/user additions with the project's devcontainer.json.

Usage

Install the extension alongside Dev Containers (outside of the container).

Add devcontainer-local.json to the .devcontainer folder:

.devcontainer/
├── devcontainer.json
└── devcontainer-local.json

# .gitignore
.devcontainer/devcontainer-local
.devcontainer/devcontainer-local.json

Or add devcontLocal.commonConfiguration in the user or workspace settings:

"devcontLocal.commonConfiguration": {
    "features": {...},
    "mounts": {...},
    ...
}

Press F1, choose Merge Configs, then Rebuild and Reopen in Container and pick the configuration from the devcontainer-local folder.

After edits, the merged devcontainer.json should update automatically.

Examples

Use an updated base image:

// devcontainer-local.json
{
    "image": "ubuntu:latest"
}

Add a mount to all containers[^1]:

// user settings
"devcontLocal.commonConfiguration": {
    "mounts": [
        "type=bind,source=${localEnv:HOME}/.bash_aliases,target=/home/vscode/.bash_aliases,readonly"
    ]
}

Remove an unused feature[^2]:

{
    "features": {
        "remove:ghcr.io/devcontainers/features/docker-in-docker:3": null
    }
}

Limit installed packages[^3]:

{
    "features": {
        "ghcr.io/devcontainers/features/python:1": {
            "toolsToInstall": "ruff,uv"
        }
    }
}

Replace post start commands[^4]:

{
    "replace:postStartCommand": {
        "another-manager": "npm install"
    }
}

Ensure that a feature builds first:

{
    "overrideFeatureInstallOrder": [
        "ghcr.io/wrwrwr/devcont-feats/apt-https"
    ]
}

[^1]: By default, objects are merged and arrays extended. [^2]: Note the remove: prefix, the value is ignored. [^3]: Scalar values are overridden. [^4]: Without the replace: prefix, a base object-type value would be merged.

Notes

The extension has some logging – if it doesn't do what it should, take a look at the Output → Dev Containers: Local Add-on tab.

License: MIT
Status: Experimental (non-transcribed TS, only tested on desktop/Ubuntu)
Assisted: Code review, additional test cases and icon drawing by Copilot