Yea, unsure how this replaces compose or how it would work in pods. Is there some kind of runtime planned to replace container.io so that you still get all the k8s orchestration (live/readiness, anti affininity, cgroups limits etc).

The way this works is it uses a containerd shim. In containerd-land, shims are responsible for all the platform dependent setup/management of a container.

The "normal" shim on Linux is the runc shim (io.containerd.runc.v2). On Windows the shim is called runhcs (io.containerd.runhcs.v1).

The docker solution mentioned in the article modifies the "wasmtime" shim from https://github.com/containerd/runwasi so that it uses "wasmedge" instead. It also happens to be using an unreleased version of dockerd.

So how does this work with compose? Currently you need to specify the runtime for the container, there should be an option in the compose yaml for this.

How does it work with pods? You need to configure containerd's cri config with a runtime handler that specifies the wasmedge shim. Then you add a RuntimeClass to k8s and add that to your pod spec.

WebAssembly is a binary format executed in a virtual machine. By default, the execution is isolated from the host OS, so that there is no concept of syscall to the OS directly from your WebAssembly module. The WASM module calls to certain exports (the WASI layer) whose endpoints are implemented by the runtime. However, the runtime in this case has the ability to decide whether and how this call that would correspond to a syscall directly had it been run on the OS directly will be mapped to the OS in reality. You might want to map that to a syscall on a real OS, or the Wasmtime runtime could be running in an embedded environment where there is no OS as we might otherwise assume.

WebAssembly also allows for powerful constructs like the component model, where components written in even different languages can interact between them.

Can you address the question about needing to compile all dependencies….

Sure, after you name an example of a programming language where neither you nor someone else has to compile the dependencies for a given program.