Webassembly

There are 3 things you need to do to run a WebAssembly module with youki.

1. Build youki with wasm-wasmer feature flag enabled
2. Build a container image with the WebAssembly module
3. Run the container with youki

Build youki with wasm-wasmedge, wasm-wasmer, or wasm-wasmtime feature flag enabled

• Run build.sh with -f wasm-wasmedge option.

  ./scripts/build.sh -o . -r -f wasm-wasmedge
  

• Run build.sh with -f wasm-wasmer option.

  ./scripts/build.sh -o . -r -f wasm-wasmer
  

• Run build.sh with -f wasm-wasmtime option.

  ./scripts/build.sh -o . -r -f wasm-wasmtime
  

Build a container image with the WebAssembly module

If you want to run a webassembly module with youki, your config.json has to include either runc.oci.handler or module.wasm.image/variant=compat".

It also needs to specify a valid .wasm (webassembly binary) or .wat (webassembly test) module as entrypoint for the container. If a wat module is specified it will be compiled to a wasm module by youki before it is executed. The module also needs to be available in the root filesystem of the container obviously.

"ociVersion": "1.0.2-dev",
"annotations": {
    "run.oci.handler": "wasm"
},
"process": {
    "args": [
        "hello.wasm",
        "hello",
        "world"
    ],
...
}
...

Compile a sample wasm module

A simple wasm module can be created by running

rustup target add wasm32-wasi
cargo new wasm-module --bin
cd ./wasm-module
vi src/main.rs

fn main() {
    println!("Printing args");
    for arg in std::env::args().skip(1) {
        println!("{}", arg);
    }

    println!("Printing envs");
    for envs in std::env::vars() {
        println!("{:?}", envs);
    }  
}

Then compile the program to WASI.

cargo build --target wasm32-wasi

Build a container image with the module

Create a Dockerfile.

vi Dockerfile

FROM scratch
COPY target/wasm32-wasi/debug/wasm-module.wasm /
ENTRYPOINT ["wasm-module.wasm"]

Then build a container image with module.wasm.image/variant=compat annotation. ¹

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

Run the wasm module with youki and podman

Run podman with youki as runtime. ¹

sudo podman --runtime /PATH/WHARE/YOU/BUILT/WITH/WASM-WASMER/youki run localhost/wasm-module 1 2 3