DevContainers // Manski's Dev Log

A collection of notes on DevContainers (especially the VSCode integration).

Basics #

To use DevContainers, you need to create a file named .devcontainer/devcontainers.json in your project. For contents, see below.

Notes and tips:

To open a terminal inside the DevContainer, call “Terminal: Create New Terminal” from the VSCode command palette.
On Windows, this requires Docker to run as “Linux containers” (not “Windows containers”) - and ideally in WSL.

Links #

Minimal Example #


//
// General notes on DevContainers: https://manski.net/articles/containers/devcontainers
//
// Format of this file: https://aka.ms/devcontainer.json
//
{
    "image": "mcr.microsoft.com/devcontainers/base:ubuntu"
}

Note

You can’t set the name of the devcontainer as Docker sees/displays it.

Extended Example with Dockerfile #

devcontainers.json #


//
// General notes on DevContainers: https://manski.net/articles/containers/devcontainers
//
// Format of this file: https://aka.ms/devcontainer.json
//
{
    // This name appears in the lower left corner in VSCode when running inside this DevContainer.
    "name": "Hugo",

    "build": {
        "dockerfile": "Dockerfile"
    },

    "runArgs": [
        // Specify DNS search domain (so that machine names can be unqualified - e.g. "my-server" instead
        // of "my-server.fritz.box").
        "--dns-search=fritz.box"
    ],

    // Container Features
    // NOTE: Features may only be available for certain distros (often, only Debian/Ubuntu is supported but not Alpine).
    // All available features: https://containers.dev/features
    // Specification: https://containers.dev/implementors/features/
    "features": {
        "ghcr.io/devcontainers/features/common-utils:2": {
            "installZsh": "true",
            //"username": "node",
            "upgradePackages": "true"
        }/*,
        "ghcr.io/devcontainers/features/node:1": {
            "version": "none"
        },
        "ghcr.io/devcontainers/features/git:1": {
            "version": "latest",
            "ppa": "false"
        }*/
    },

    // Configure tool-specific properties.
    "customizations": {
        // Configure properties specific to VS Code.
        "vscode": {
            // Add the IDs of extensions you want installed when the container is created.
            "extensions": [
                "editorconfig.editorconfig",
                "davidanson.vscode-markdownlint",
                "streetsidesoftware.code-spell-checker",
                "ms-azuretools.vscode-docker"
            ]
        }
    },

    // Set *default* container specific settings.json values on container create.
    /*"settings": {
        "php.validate.executablePath": "/usr/local/bin/php"
    },

    */

    // Use 'forwardPorts' to make a list of ports inside the container available locally.
    "forwardPorts": [1313],

    // Use 'postCreateCommand' to run commands after the container is created.
    //"postCreateCommand": "yarn install --prod",

    // Use non-root user. More info: https://aka.ms/vscode-remote/containers/non-root.
    "remoteUser": "vscode",

    // Mount the workspace in a predictable location (because - by default - the workspace would be mounted
    // under the folder name the user chose for the workspace - e.g. "/workspaces/ansible-workbench").
    "workspaceMount": "source=${localWorkspaceFolder},target=/workspace,type=bind",
    "workspaceFolder": "/workspace"
}

Dockerfile #


# See: https://hugomods.com/docs/docker/
# Image is Alpine based and contains both NodeJS and Git.
FROM hugomods/hugo

# Add Git LFS (not installed by default).
RUN apk add --no-cache git-lfs

EXPOSE 1313

SSH Troubleshooting #

Normally, VSCode automatically forwards the host’s ssh-agent into the DevContainer. Here’s how this normally works and that can give you a hint at where the problem is.

To see, if ssh works inside the devcontainer (i.e. the ssh-agent from the host is correctly routed to the container), execute:


$ ssh-add -l
4096 SHA256:WJ2WxTG1F4bHWq29eN+lvc/5VYLhjAZp5b5555PkGis Primary SSH Key (RSA)

If this gives you an error, check $SSH_AUTH_SOCK:


$ echo $SSH_AUTH_SOCK
/tmp/vscode-ssh-auth-2d206968-2061-406b-8a9f-a4a2249dc649.sock

If this variable is empty, search the contents of the container log (F1 > Dev Containers: Show Container Log) for “SSH_AUTH_SOCK”:


[16730 ms] Start: Launching Dev Containers helper.
[16730 ms] ssh-agent: SSH_AUTH_SOCK not set on local host.
[16732 ms] ssh-agent: SSH_AUTH_SOCK in container (/tmp/vscode-ssh-auth-2d206968-2061-406b-8a9f-a4a5349dc649.sock) forwarded to local host (\\.\pipe\openssh-ssh-agent).

If this doesn’t work and you are on Windows, it may help to manually set the SSH_AUTH_SOCK environment variable to \\.\pipe\openssh-ssh-agent (source).