Running WebAssembly workloads with Podman

WebAssembly (abbreviated Wasm) is a portable binary instruction format. It has gained popularity for its portability as a compilation target that enables deployment on the web for both client and server applications.

We can leverage the portability of Wasm to run Wasm workloads alongside Linux containers by combining crun and Podman. crun supports running Wasm workload by using WasmEdge, Wasmtime, or Wasmer runtimes. While Podman defaults to runc, runc, and crun can be used interchangeably.

WasmEdge is a lightweight, high-performance, and extensible WebAssembly runtime for cloud-native and edge applications. WasmEdge was recently added to openSUSE Tumbleweed and this can give us support for Wasm workloads on containers if we enable an experimental feature in crun.

Now that we have WasmEdge in openSUSE Tumbleweed and crun experimental support for Wasm workloads we can run WebAssembly workloads on Podman. This new feature was introduced into Podman in Tumbleweed and also a new package. The blog post shows how to use it.

Preparing our environment

We first need to install crun as runc in the default OCI runtime for Podman.

zypper in crun

Once crun is installed check if you have Wasm support.

$ crun -v
crun version 1.9
commit: a538ac4ea1ff319bcfe2bf81cb5c6f687e2dc9d3
rundir: /run/user/1000/crun
spec: 1.0.0
+SYSTEMD +SELINUX +APPARMOR +CAP +SECCOMP +EBPF +CRIU +LIBKRUN +WASM:wasmedge +YAJL

In the above output, we can see that crun supports WasmEdge (+WASM:wasmedge).

Preparing our application

We are going to create a simple “Hello” application in Rust.

First, ensure you have Rust and WasmEdge installed.

zypper in rust wasmedge

Now let’s create our “Hello” application in Rust.

$ cargo new hello --bin
$ cd hello

Change the message in src/main.rs to Hello WebAssembly! or any other message you want.

Now let’s compile our application, but the target machine will be Wasm.

$ cargo build --target wasm32-wasi

We can now execute the binary we just compiled and check that it works as expected.

$ wasmedge run target/wasm32-wasi/debug/hello.wasm
Hello WebAssembly!

You have successfully built your Wasm application.

Creating a Wasm container

With our Wasm binary in hand, let’s add it to a container.

Create a file named Containerfile and add the following to it:

FROM scratch
COPY target/wasm32-wasi/debug/hello.wasm /
CMD ["/hello.wasm"]

Let’s build our Wasm container with Buildah.

$ buildah build --platform=wasi/wasm -t hello-wasm .

You should have a Wasm container by now.

Running a Wasm workload

Let’s run our Wasm container with Podman.

$ podman run --rm hello-wasm
Hello WebAssembly!

Great, we have a working Wasm container.

Conclusion

WebAssembly is a fairly recent topic, but it has gained a lot of attention because you can reuse most of what you already know or use and easily port applications.

Running a native Wasm container is another example of how portable this format is.