crun/docs/wasm-wasi-example.md

crun-wasi-wasm example

• Make sure oci config contains handler for wasm or image contains annotation module.wasm.image/variant=compat.
• Entrypoint must point to a valid .wat (webassembly text) or .wasm (webassembly binary).

...
"annotations": {
 "run.oci.handler": "wasm"
},
...

Examples

Try out example with pre-built image and podman.

podman run -it -p 8080:8080  --name=wasm-example  --platform=wasi/wasm32   michaelirwin244/wasm-example

Compiling and running wasm modules

• Following example is using rust to compile a webassembly module but you can use any supported language.
• Create a new rust binary using cargo new hello_wasm --bin.
• Add relevant function to src/main.rs for this example we will be using a print.

 fn main() {
  println!("{}", "This is from a main function from a wasm module");
 }

• Compile to wasm32-wasip1 target using wasm-pack or any other relevant tool. We are going to be using cargo build --target wasm32-wasip2
• Create relevant image and use your container manager. But for this example we will be running directly using crun and plub config manually.

$ crun run wasm-container
This is from a main function from a wasm module

Running OCI wasm compat images with buildah and podman

• Compile your .wasm module using instructions from step one.
• Prepare a Containerfile with your .wasm module.

FROM scratch
COPY hello.wasm /
CMD ["/hello.wasm"]

• Build wasm image using buildah

$ buildah build --platform=wasi/wasm -t mywasm-image .

• Make sure your podman points to oci runtime crun build with wasm support.
• Run image using podman

$ podman run mywasm-image:latest
This is from a main function from a wasm module