This is a project to facilitate running wasm workloads managed by containerd either directly (ie. through ctr) or as directed by Kubelet via the CRI plugin. It is intended to be a (rust) library that you can take and integrate with your wasm host. Included in the repository is a PoC for running a plain wasi host (ie. no extra host functions except to support wasi system calls).

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runwasi is intended to be consumed as a library to be linked to from your own wasm host implementation. It creates one shim process per container or k8s pod.

You need to implement a trait to teach runwasi how to use your wasm host.

There are two ways to do this:

• implementing the sandbox::Instance trait
• or implementing the container::Engine trait

The most flexible but complex is the sandbox::Instance trait:

pub trait Instance {
    /// The WASI engine type
    type Engine: Send + Sync + Clone;

    /// Create a new instance
    fn new(id: String, cfg: Option<&InstanceConfig<Self::E>>) -> Self;
    /// Start the instance
    /// The returned value should be a unique ID (such as a PID) for the instance.
    /// Nothing internally should be using this ID, but it is returned to containerd where a user may want to use it.
    fn start(&self) -> Result<u32, Error>;
    /// Send a signal to the instance
    fn kill(&self, signal: u32) -> Result<(), Error>;
    /// Delete any reference to the instance
    /// This is called after the instance has exited.
    fn delete(&self) -> Result<(), Error>;
    /// Wait for the instance to exit
    /// The waiter is used to send the exit code and time back to the caller
    /// Ideally this would just be a blocking call with a normal result, however
    /// because of how this is called from a thread it causes issues with lifetimes of the trait implementer.
    fn wait(&self, waiter: &Wait) -> Result<(), Error>;
}

The container::Engine trait provides a simplified API:

pub trait Engine: Clone + Send + Sync + 'static {
    /// The name to use for this engine
    fn name() -> &'static str;
    /// Run a WebAssembly container
    fn run_wasi(&self, ctx: &impl RuntimeContext, stdio: Stdio) -> Result<i32>;
    /// Check that the runtime can run the container.
    /// This checks runs after the container creation and before the container starts.
    /// By default it checks that the wasi_entrypoint is either:
    /// * a OCI image with wasm layers
    /// * a file with the `wasm` filetype header
    /// * a parsable `wat` file.
    fn can_handle(&self, ctx: &impl RuntimeContext) -> Result<()> { /* default implementation*/ }
}

After implementing container::Engine you can use container::Instance<impl container::Engine>, which implements the sandbox::Instance trait.

To use your implementation in "normal" mode, you'll need to create a binary which has a main that looks something like this:

use containerd_shim as shim;
use containerd_shim_wasm::sandbox::{ShimCli, Instance}

struct MyInstance {
    // ...
}

impl Instance for MyInstance {
    // ...
}

fn main() {
    shim::run::<ShimCli<MyInstance>>("io.containerd.myshim.v1", opts);
}

or when using the container::Engine trait, like this:

use containerd_shim as shim;
use containerd_shim_wasm::{sandbox::ShimCli, container::{Instance, Engine}}

struct MyEngine {
    // ...
}

impl Engine for MyEngine {
    // ...
}

fn main() {
    shim::run::<ShimCli<Instance<Engine>>>("io.containerd.myshim.v1", opts);
}

Note you can implement your own ShimCli if you like and customize your wasm engine and other things. I encourage you to checkout how that is implemented.

The shim binary just needs to be installed into $PATH (as seen by the containerd process) with a binary name like containerd-shim-myshim-v1.

Check out these projects that build on top of runwasi:

• spinkube/containerd-shim-spin
• deislabs/containerd-wasm-shims

• containerd-shim-[ wasmedge | wasmtime | wasmer | wamr ]-v1

This is a containerd shim which runs wasm workloads in WasmEdge or Wasmtime or Wasmer. You can use it with containerd's ctr by specifying --runtime=io.containerd.[ wasmedge | wasmtime | wasmer | wamr ].v1 when creating the container. And make sure the shim binary must be in $PATH (that is the $PATH that containerd sees). Usually you just run make install after make build.

build shim with wasmedge we need install library first

This shim runs one per pod.

To begin contributing, learn to build and test the project or to add a new shim please read our CONTRIBUTING.md

Make sure you have installed dependencies and install the shims:

make build
sudo make install

Note: make build will only build one binary. The make install command copies the binary to $PATH and uses symlinks to create all the component described above.

Build the test image and load it into containerd:

make test-image
make load

Run it with sudo ctr run --rm --runtime=io.containerd.[ wasmedge | wasmtime | wasmer | wamr ].v1 ghcr.io/containerd/runwasi/wasi-demo-app:latest testwasm /wasi-demo-app.wasm echo 'hello'. You should see some output repeated like:

sudo ctr run --rm --runtime=io.containerd.wasmtime.v1 ghcr.io/containerd/runwasi/wasi-demo-app:latest testwasm

This is a song that never ends.
Yes, it goes on and on my friends.
Some people started singing it not knowing what it was,
So they'll continue singing it forever just because...

This is a song that never ends.
Yes, it goes on and on my friends.
Some people started singing it not knowing what it was,
So they'll continue singing it forever just because...

(...)

To kill the process, you can run in other session: sudo ctr task kill -s SIGKILL testwasm.

The test binary supports commands for different type of functionality, check crates/wasi-demo-app/src/main.rs to try it out.

The previous demos run with an OCI Container image containing the wasm module in the file system. Another option is to provide a cross-platform OCI Image that that will not have the wasm module or components in the file system of the container that wraps the wasmtime/wasmedge process. This OCI Image with custom WASM layers can be run across any platform and provides for de-duplication in the Containerd content store among other benefits. To build OCI images using your own images you can use the oci-tar-builder

To learn more about this approach checkout the design document.

Note: This requires containerd 1.7.7+ and 1.6.25+. If you do not have these patches for both containerd and ctr you will end up with an error message such as mismatched image rootfs and manifest layers at the import and run steps. Latest versions of k3s and kind have the necessary containerd versions.

Build and import the OCI image with WASM layers image:

make test-image/oci
make load/oci

Run the image with sudo ctr run --rm --runtime=io.containerd.[ wasmedge | wasmtime | wasmer | wamr ].v1 ghcr.io/containerd/runwasi/wasi-demo-oci:latest testwasmoci

sudo ctr run --rm --runtime=io.containerd.wasmtime.v1 ghcr.io/containerd/runwasi/wasi-demo-oci:latest testwasmoci wasi-demo-oci.wasm echo 'hello'
hello
exiting

The CNCF tag-runtime wasm working group has a OCI Artifact format for Wasm. This is a new Artifact type that enable the usage across projects beyond just runwasi, see the https://tag-runtime.cncf.io/wgs/wasm/deliverables/wasm-oci-artifact/#implementations

make test-image/oci
make load/oci
make test/k8s-oci-wasmtime

note: We are using a kubernetes cluster to run here since containerd's ctr has a bug that results in ctr: unknown image config media type application/vnd.wasm.config.v0+json

See wasmtime-shim documentation.