docs/desktop/extensions-sdk/build/backend-extension-tutorial.md

title	description	keywords	redirect_from
Add a backend to your extension	Learn how to add a backend to your extension.	Docker, extensions, sdk, build	/desktop/extensions-sdk/tutorials/minimal-backend-extension/ /desktop/extensions-sdk/build/minimal-backend-extension/ /desktop/extensions-sdk/build/set-up/backend-extension-tutorial/

Your extension can ship a backend part with which the frontend can interact with. This page provides information on why and how to add a backend.

Note

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

Note

Check the Quickstart guide and docker extension init <my-extension>. They provide a better base for your extension as it's more up-to-date and related to your install of Docker Desktop.

Why add a backend?

Thanks to the Docker Extensions SDK, most of the time you should be able to do what you need from the Docker CLI directly from the frontend.

Nonetheless, there are some cases where you might need to add a backend to your extension. So far, extension builders have used the backend to:

• Store data in a local database and serve them back with a REST API.
• Store the extension state, like when a button starts a long-running process, so that if you navigate away from the extension user interface and come back, the frontend can pick up where it left off.

Learn more about extension backend in the architecture section.

Add a backend to the extension

If you created your extension using the docker extension init command, you already have a backend setup. If it is not the case, then you have to first create a vm directory that will contain the code and update the Dockerfile to containerize it.

Here is the extension folder structure with a backend:

.
├── Dockerfile # (1)
├── Makefile
├── metadata.json
├── ui
    └── index.html
└── vm # (2)
    ├── go.mod
    └── main.go

1. Contains everything required to build the backend and copy it in the extension's container filesystem.
2. The source folder that contains the backend code of the extension

Although you can start from an empty directory or from the vm-ui extension sample{:target="blank" rel="noopener" class=""}, it is highly recommended that you start from the docker extension init command and change it to suit your needs.

Tip

The docker extension init generates a Go backend. But you can still use it as a starting point for your own extension and use any other language like Node.js, Python, Java, .Net, or any other language and framework. {: .tip }

On this tutorial, the backend service simply exposes one route that returns a JSON payload that says "Hello".

{ "Message": "Hello" }

Important

We recommend that, the frontend and the backend communicate through sockets (and named pipes on Windows) instead of HTTP. On one hand, because it will prevent port collision with any other running application or container running on the host. On the other hand, because some Docker Desktop users are running in constrained environments where they can't open ports on their machines. So, when choosing the language and framework for your backend, make sure it supports sockets connection. {: .important}

• Go
• Node
• Python
• Java
• .Net

package main

import (
	"flag"
	"log"
	"net"
	"net/http"
	"os"

	"github.com/labstack/echo"
	"github.com/sirupsen/logrus"
)

func main() {
	var socketPath string
	flag.StringVar(&socketPath, "socket", "/run/guest/volumes-service.sock", "Unix domain socket to listen on")
	flag.Parse()

	os.RemoveAll(socketPath)

	logrus.New().Infof("Starting listening on %s\n", socketPath)
	router := echo.New()
	router.HideBanner = true

	startURL := ""

	ln, err := listen(socketPath)
	if err != nil {
		log.Fatal(err)
	}
	router.Listener = ln

	router.GET("/hello", hello)

	log.Fatal(router.Start(startURL))
}

func listen(path string) (net.Listener, error) {
	return net.Listen("unix", path)
}

func hello(ctx echo.Context) error {
	return ctx.JSON(http.StatusOK, HTTPMessageBody{Message: "hello world"})
}

type HTTPMessageBody struct {
	Message string
}

Important

We don't have a working example for Node yet. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a sample for Node. {: .important }

Important

We don't have a working example for Python yet. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a sample for Python. {: .important }

Important

We don't have a working example for Java yet. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a sample for Java. {: .important }

Important

We don't have a working example for .Net. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a sample for .Net. {: .important }

Adapt the Dockerfile

Note

When using the docker extension init, it creates a Dockerfile that already contains what is needed for a Go backend.

• For Go
• For Node
• For Python
• For Java
• .For Net

To deploy your Go backend when installing the extension, you need first to configure the Dockerfile, so that:

• it builds the backend application
• it copies the binary in the extension's container filesystem
• it starts the binary when the container starts listening on the extension socket

Tip

To ease version management, you can reuse the same image to build the frontend, build the backend service, and package the extension. {: .tip }

# syntax=docker/dockerfile:1
FROM node:17.7-alpine3.14 AS client-builder
# ... build frontend application

# Build the Go backend
FROM golang:1.17-alpine AS builder
ENV CGO_ENABLED=0
WORKDIR /backend
COPY vm/go.* .
RUN --mount=type=cache,target=/go/pkg/mod \
    --mount=type=cache,target=/root/.cache/go-build \
    go mod download
COPY vm/. .
RUN --mount=type=cache,target=/go/pkg/mod \
    --mount=type=cache,target=/root/.cache/go-build \
    go build -trimpath -ldflags="-s -w" -o bin/service

FROM alpine:3.15
# ... add labels and copy the frontend application

COPY --from=builder /backend/bin/service /
CMD /service -socket /run/guest-services/extension-allthethings-extension.sock

Important

We don't have a working Dockerfile for Node yet. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a Dockerfile for Node. {: .important }

Important

We don't have a working Dockerfile for Python yet. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a Dockerfile for Python. {: .important }

Important

We don't have a working Dockerfile for Java yet. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a Dockerfile for Java. {: .important }

Important

We don't have a working Dockerfile for .Net. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a Dockerfile for .Net. {: .important }

Configure the metadata file

To start the backend service of your extension inside the VM of Docker Desktop, you have to configure the image name in the vm section of the metadata.json file.

{
  "vm": {
    "image": "${DESKTOP_PLUGIN_IMAGE}"
  },
  "icon": "docker.svg",
  "ui": {
    ...
  }
}

For more information on the vm section of the metadata.json, see Metadata.

Warning

Do not replace the ${DESKTOP_PLUGIN_IMAGE} placeholder in the metadata.json file. The placeholder is replaced automatically with the correct image name when the extension is installed. {: .warning}

Invoke the extension backend from your frontend

Using the advanced frontend extension example, we can invoke our extension backend.

Use the Docker Desktop Client object and then invoke the /hello route from the backend service with ddClient. extension.vm.service.get that returns the body of the response.

• React
• Vue
• Angular
• Svelte

Replace the ui/src/App.tsx file with the following code:

{% raw %}
// ui/src/App.tsx
import React, { useEffect } from 'react';
import { createDockerDesktopClient } from "@docker/extension-api-client";

//obtain docker destkop extension client
const ddClient = createDockerDesktopClient();

export function App() {
  const ddClient = createDockerDesktopClient();
  const [hello, setHello] = useState<string>();

  useEffect(() => {
    const getHello = async () => {
      const result = await ddClient.extension.vm?.service?.get('/hello');
      setHello(JSON.stringify(result));
    }
    getHello()
  }, []);

  return (
    <Typography>{hello}</Typography>
  );
}
{% endraw %}

Important

We don't have an example for Vue yet. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a sample with Vue. {: .important }

Important

We don't have an example for Angular yet. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a sample with Angular. {: .important }

Important

We don't have an example for Svelte yet. Fill out the form{: target="blank" rel="noopener" class=""} and let us know you'd like a sample with Svelte. {: .important }

Re-build the extension and update it

Since you have modified the configuration of the extension and added a stage in the Dockerfile, you must build again the extension.

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

Once built, you need to update it (or install it if you haven't done it yet).

docker extension update awesome-inc/my-extension:latest

Now you can see the backend service running in the containers tab of the Docker Desktop Dashboard and watch the logs when you need to debug it.

Tip

You may need to enable the "Show system containers" option in Docker Desktop to see the backend container running under the extension compose project in the containers tab of the dashboard. See how to show extension containers for more information. {: .tip }

Open Docker Desktop Dashboard and click on the containers tab. You should see the response from the backend service call displayed.

What's next?

• Learn how to share and publish your extension.
• Learn more about extensions architecture.