- Copies the binary in the extension's container filesystem
- 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.

```dockerfile
# 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
```

{{< /tab >}}
{{< tab name="Node" >}}

> [!IMPORTANT]
>
> We don't have a working Dockerfile for Node yet. [Fill out the form](https://docs.google.com/forms/d/e/1FAIpQLSdxJDGFJl5oJ06rG7uqtw1rsSBZpUhv_s9HHtw80cytkh2X-Q/viewform?usp=pp_url&entry.25798127=Node)
> and let us know if you'd like a Dockerfile for Node.

{{< /tab >}}
{{< tab name="Python" >}}

> [!IMPORTANT]
>
> We don't have a working Dockerfile for Python yet. [Fill out the form](https://docs.google.com/forms/d/e/1FAIpQLSdxJDGFJl5oJ06rG7uqtw1rsSBZpUhv_s9HHtw80cytkh2X-Q/viewform?usp=pp_url&entry.25798127=Python)
> and let us know if you'd like a Dockerfile for Python.

{{< /tab >}}
{{< tab name="Java" >}}

> [!IMPORTANT]
>
> We don't have a working Dockerfile for Java yet. [Fill out the form](https://docs.google.com/forms/d/e/1FAIpQLSdxJDGFJl5oJ06rG7uqtw1rsSBZpUhv_s9HHtw80cytkh2X-Q/viewform?usp=pp_url&entry.25798127=Java)
> and let us know if you'd like a Dockerfile for Java.

{{< /tab >}}
{{< tab name=".NET" >}}

> [!IMPORTANT]
>
> We don't have a working Dockerfile for .Net. [Fill out the form](https://docs.google.com/forms/d/e/1FAIpQLSdxJDGFJl5oJ06rG7uqtw1rsSBZpUhv_s9HHtw80cytkh2X-Q/viewform?usp=pp_url&entry.25798127=.Net)
> and let us know if you'd like a Dockerfile for .Net.

{{< /tab >}}
{{< /tabs >}}

## 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.

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

For more information on the `vm` section of the `metadata.json`, see [Metadata](../architecture/metadata.md).

> [!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.

## Invoke the extension backend from your frontend

Using the [advanced frontend extension example](frontend-extension-tutorial.md), we can invoke our extension backend.