HTTP server example

Let's build a container image for a WebAssembly HTTP service. The HTTP service application is developed in Rust using the WasmEdge networking socket API. Kubernetes could manage the wasm application lifecycle with CRI-O, Docker and Containerd.


This is a Rust example, which require you to install Rust and WasmEdge before you can Compile and Run the http service.

Download example code

mkdir http_server
cd http_server
wget -q
mkdir src
cd src
wget -q
cd ../

Build the WASM bytecode

rustup target add wasm32-wasi
cargo build --target wasm32-wasi --release

The wasm bytecode application is now should be located in the ./target/wasm32-wasi/release/http_server.wasm You can now test run it with wasmedge and then publish it as a container image.

Apply executable permission on the Wasm bytecode

chmod +x ./target/wasm32-wasi/release/http_server.wasm

Running the http_server application bytecode with wasmedge

When you run the bytecode with wasmedge and see the result as the following, you are ready to package the bytecode into the container.

wasmedge ./target/wasm32-wasi/release/http_server.wasm
new connection at 1234

You can test the server from another terminal window.

$ curl -X POST -d 'name=WasmEdge'
echo: name=WasmEdge

Create Dockerfile

Create a file called Dockerfile in the target/wasm32-wasi/release/ folder with the following content:

FROM scratch
ADD http_server.wasm /
CMD ["/http_server.wasm"]

Create container image with annotations

Please note that adding self-defined annotation is still a new feature in buildah.

The crun container runtime can start the above WebAssembly-based container image. But it requires the module.wasm.image/variant=compat annotation on the container image to indicate that it is a WebAssembly application without a guest OS. You can find the details in Official crun repo.

To add module.wasm.image/variant=compat annotation in the container image, you will need the latest buildah. Currently, Docker does not support this feature. Please follow the install instructions of buildah to build the latest buildah binary.

Build and install the latest buildah on Ubuntu

On Ubuntu zesty and xenial, use these commands to prepare for buildah.

sudo apt-get -y install software-properties-common

export OS="xUbuntu_20.04"
sudo bash -c "echo \"deb$OS/ /\" > /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list"
sudo bash -c "curl -L$OS/Release.key | apt-key add -"

sudo add-apt-repository -y ppa:alexlarsson/flatpak
sudo apt-get -y -qq update

sudo apt-get -y install bats git libapparmor-dev libdevmapper-dev libglib2.0-dev libgpgme-dev libseccomp-dev libselinux1-dev skopeo-containers go-md2man containers-common
sudo apt-get -y install golang-1.16 make

Then, follow these steps to build and install buildah on Ubuntu.

mkdir -p ~/buildah
cd ~/buildah
export GOPATH=`pwd`
git clone ./src/
cd ./src/
PATH=/usr/lib/go-1.16/bin:$PATH make
cp bin/buildah /usr/bin/buildah
buildah --help

Create and publish a container image with buildah

In the target/wasm32-wasi/release/ folder, do the following.

sudo buildah build --annotation "module.wasm.image/variant=compat" -t http_server .

# make sure docker is install and running
# systemctl status docker
# to make sure regular user can use docker
# sudo usermod -aG docker $USER#
# newgrp docker

# You may need to use docker login to create the `~/.docker/config.json` for auth.
# docker login

sudo buildah push --authfile ~/.docker/config.json http_server docker://

That's it! Now you can try to run it in CRI-O or Kubernetes!