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.
Prerequisites
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 https://raw.githubusercontent.com/second-state/wasmedge_wasi_socket/main/examples/http_server/Cargo.toml
mkdir src
cd src
wget -q https://raw.githubusercontent.com/second-state/wasmedge_wasi_socket/main/examples/http_server/src/main.rs
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 http://127.0.0.1:1234 -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 https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/ /\" > /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list"
sudo bash -c "curl -L https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$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 https://github.com/containers/buildah ./src/github.com/containers/buildah
cd ./src/github.com/containers/buildah
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://docker.io/avengermojo/http_server:with-wasm-annotation
That’s it! Now you can try to run it in CRI-O or Kubernetes!