Create a simple extension

Table of contents

To start creating your extension, you first need a directory with files which range from the extension’s source code to the required extension-specific files. This page provides information on how to set up a minimal frontend extension based on plain HTML.

Before you start, make sure you have installed the latest version of Docker Desktop.

Tip

If you want to start a codebase for your new extension, our Quickstart guide and docker extension init <my-extension> provides a better base for your extension.

Extension folder structure

In the minimal-frontend sample folder, you can find a ready-to-go example that represents a UI Extension built on HTML. We will go through this code example in this tutorial.

Although you can start from an empty directory, it is highly recommended that you start from the template below and change it accordingly to suit your needs.

.
├── Dockerfile # (1)
├── metadata.json # (2)
└── ui # (3)
    └── index.html
  1. Contains everything required to build the extension and run it in Docker Desktop.
  2. A file that provides information about the extension such as the name, description, and version.
  3. The source folder that contains all your HTML, CSS and JS files. There can also be other static assets such as logos and icons. For more information and guidelines on building the UI, see the Design and UI styling section.

Create a Dockerfile

At a minimum, your Dockerfile needs:

  • Labels which provide extra information about the extension, icon and screenshots.
  • The source code which in this case is an index.html that sits within the ui folder.
  • The metadata.json file.
# syntax=docker/dockerfile:1
FROM scratch

LABEL org.opencontainers.image.title="Minimal frontend" \
    org.opencontainers.image.description="A sample extension to show how easy it's to get started with Desktop Extensions." \
    org.opencontainers.image.vendor="Awesome Inc." \
    com.docker.desktop.extension.api.version="0.3.3" \
    com.docker.desktop.extension.icon="https://www.docker.com/wp-content/uploads/2022/03/Moby-logo.png"

COPY ui ./ui
COPY metadata.json .

Configure the metadata file

A metadata.json file is required at the root of the image filesystem.

{
  "ui": {
    "dashboard-tab": {
      "title": "Minimal frontend",
      "root": "/ui",
      "src": "index.html"
    }
  }
}

For more information on the metadata.json, see Metadata.

Build the extension and install it

Now that you have configured the extension, you need to build the extension image that Docker Desktop will use to install it.

$ docker build --tag=awesome-inc/my-extension:latest .

This built an image tagged awesome-inc/my-extension:latest, you can run docker inspect awesome-inc/my-extension:latest to see more details about it.

Finally, you can install the extension and see it appearing in the Docker Desktop Dashboard.

$ docker extension install awesome-inc/my-extension:latest

Preview the extension

To preview the extension in Docker Desktop, close and open the Docker Desktop Dashboard once the installation is complete.

The left-hand menu displays a new tab with the name of your extension.

Minimal frontend extension

What's next?