Docker+Wasm (Beta)

Wasm (short for WebAssembly) is a fast, light alternative to the Linux and 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.

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.

Turn on the Docker+Wasm integration

To use the Docker+Wasm integration, developers must turn on the containerd image store feature.

Important

The Docker+Wasm integration requires the containerd image store feature. If you’re not already using the containerd image store, then pre-existing images and containers will be inaccessible.

Usage examples

Running a Wasm application with docker run

The following docker run command starts a Wasm container on your system:

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

After running this command, you can visit http://localhost:8080/ to see the “Hello world” output from this example module.

Got an error message? Head to the troubleshooting section for help.

Note the --runtime and --platform flags used in this command:

  • --runtime=io.containerd.wasmedge.v1: informs the Docker engine that you want to use the Wasm containerd shim instead of the standard Linux container runtime
  • --platform=wasi/wasm32: 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 takes care of 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.

  1. 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.

  2. 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

    If you run docker image ls from another terminal window, you can see the Wasm image in your image store.

    $ docker image ls
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,

  3. Open the URL http://localhost:8090 in a browser and create a few sample orders. All of these are interacting with the Wasm server.

  4. 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

  1. Create a Dockerfile that builds your Wasm application.

    Exactly how to do this varies depending on the programming language you use.

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

    # syntax=docker/dockerfile:1
FROM scratch
COPY --from=build /build/hello_world.wasm /hello_world.wasm
ENTRYPOINT [ "hello_world.wasm" ]

  3. 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

Troubleshooting

This section contains instructions on how to resolve common issues.

Unknown runtime specified

If you try to run a Wasm container before you have opted in to use the containerd image store, an error similar to the following displays:

docker: Error response from daemon: Unknown runtime specified io.containerd.wasmedge.v1.

Turn on the containerd feature in Docker Desktop settings and try again.

Failed to start shim: failed to resolve runtime path

If you use an older version of Docker Desktop that doesn’t support running Wasm containers, you will see an error message similar to the following:

docker: Error response from daemon: failed to start shim: failed to resolve runtime path: runtime "io.containerd.wasmedge.v1" binary not installed "containerd-shim-wasmedge-v1": file does not exist: unknown.

Update your Docker Desktop to the latest version and try again.

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.