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Docker+Wasm (Beta)	How to use the Wasm integration in Docker Desktop	Docker, WebAssembly, wasm, containerd, engine	3

Wasm (short for WebAssembly) is a faster, lighter alternative to the Linux & Windows containers you’re using in Docker today (with some tradeoffs).

This page provides information about the new ability to run Wasm applications alongside your Linux containers in Docker. To learn more about the launch and how the preview works, read the launch blog post here.

Beta

The Docker+Wasm feature is currently in Beta. We recommend that you do not use this feature in production environments as this feature may change or be removed from future releases.

Enable the Docker+Wasm integration

The Docker+Wasm integration currently requires a technical preview build of Docker Desktop.

Warning

With the technical preview build of Docker Desktop, things might not work as expected. Be sure to back up your containers and images before proceeding. {: .warning}

Important

The technical preview build enables the Containerd Image Store feature. This cannot be disabled. If you’re not currently using the Containerd Image Store, then pre-existing images and containers will be inaccessible. {: .important}

Download the technical preview build of Docker Desktop:

macOS Apple Silicon{: id="dkr_docs_dl_wasm_apple"}
macOS Intel{: id="dkr_docs_dl_wasm_intel"}
Windows AMD64{: id="dkr_docs_dl_wasm_windows"}
Linux Arm64 (deb{: id="dkr_docs_dl_wasm_arm64deb"})
Linux AMD64 (deb{: id="dkr_docs_dl_wasm_amd64deb"}, rpm{: id="dkr_docs_dl_wasm_amd64rpm"}, tar{: id="dkr_docs_dl_wasm_amd64tar"})

Usage examples

Running a Wasm application with `docker run`

$ docker run -dp 8080:8080 \
  --name=wasm-example \
  --runtime=io.containerd.wasmedge.v1 \
  --platform=wasi/wasm32 \
  michaelirwin244/wasm-example

Note the two additional flags to the run command:

--runtime=io.containerd.wasmedge.v1. This informs the Docker engine that you want to use the Wasm containerd shim instead of the standard Linux container runtime
--platform=wasi/wasm32. This specifies the architecture of the image you want to use. By leveraging a Wasm architecture, you don’t need to build separate images for the different machine architectures. The Wasm runtime does the final step of converting the Wasm binary to machine instructions.

Running a Wasm application with Docker Compose

The same application can be run using the following Docker Compose file:

services:
  app:
    image: michaelirwin244/wasm-example
    platform: wasi/wasm32
    runtime: io.containerd.wasmedge.v1
    ports:
      - 8080:8080

Start the application using the normal Docker Compose commands:

docker compose up

Running a multi-service application with Wasm

Networking works the same as you expect with Linux containers, giving you the flexibility to combine Wasm applications with other containerized workloads, such as a database, in a single application stack.

In the following example, the Wasm application leverages a MariaDB database running in a container.

Clone the repository.

$ git clone https://github.com/second-state/microservice-rust-mysql.git
Cloning into 'microservice-rust-mysql'...
remote: Enumerating objects: 75, done.
remote: Counting objects: 100% (75/75), done.
remote: Compressing objects: 100% (42/42), done.
remote: Total 75 (delta 29), reused 48 (delta 14), pack-reused 0
Receiving objects: 100% (75/75), 19.09 KiB | 1.74 MiB/s, done.
Resolving deltas: 100% (29/29), done.

Navigate into the cloned project and start the project using Docker Compose.

$ cd microservice-rust-mysql
$ docker compose up
[+] Running 0/1
⠿ server Warning                                                                                                  0.4s
[+] Building 4.8s (13/15)
...
microservice-rust-mysql-db-1      | 2022-10-19 19:54:45 0 [Note] mariadbd: ready for connections.
microservice-rust-mysql-db-1      | Version: '10.9.3-MariaDB-1:10.9.3+maria~ubu2204'  socket: '/run/mysqld/mysqld.sock'  port: 3306  mariadb.org binary distribution

In another terminal, we can see the Wasm image that was created.

$ docker images
REPOSITORY   TAG       IMAGE ID       CREATED         SIZE
server       latest    2c798ddecfa1   2 minutes ago   3MB

Inspecting the image shows the image has a wasi/wasm32 platform. A combination of Os and Architecture.

$ docker image inspect server | grep -A 3 "Architecture"
        "Architecture": "wasm32",
        "Os": "wasi",
        "Size": 3001146,
        "VirtualSize": 3001146,

Open the website at http://localhost:8090 and create a few sample orders. All of these are interacting with the Wasm server.
When you're all done, tear everything down by hitting Ctrl+C in the terminal you launched the application.

Building and pushing a Wasm module

Create a Dockerfile that builds your Wasm application. This varies depending on the language you are using.

In a separate stage in your Dockerfile, extract the module and set it as the ENTRYPOINT.

FROM scratch
COPY --from=build /build/hello_world.wasm /hello_world.wasm
ENTRYPOINT [ "hello_world.wasm" ]

Build and push the image specifying the wasi/wasm32 architecture. Buildx makes this easy to do in a single command.

$ docker buildx build --platform wasi/wasm32 -t username/hello-world .
...
=> exporting to image                                                                             0.0s
=> => exporting layers                                                                            0.0s
=> => exporting manifest sha256:2ca02b5be86607511da8dc688234a5a00ab4d58294ab9f6beaba48ab3ba8de56  0.0s
=> => exporting config sha256:a45b465c3b6760a1a9fd2eda9112bc7e3169c9722bf9e77cf8c20b37295f954b    0.0s
=> => naming to docker.io/username/hello-world:latest                                            0.0s
=> => unpacking to docker.io/username/hello-world:latest                                         0.0s
$ docker push username/hello-world

Docker+Wasm Release Notes

2022-10-24
Initial release

New

Initial implementation of Wasm integration

Known issues

Docker Compose may not exit cleanly when interrupted
- Workaround: Clean up docker-compose processes by sending them a SIGKILL (killall -9 docker-compose).
Pushes to Hub might give an error stating server message: insufficient_scope: authorization failed, even after logging in using Docker Desktop
- Workaround: Run docker login in the CLI

Feedback

Thanks for trying the new Docker+Wasm integration. Give feedback or report any bugs you may find through the issues tracker on the public roadmap item{: target="blank" rel="noopener" class=""}.

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