Running WebAssembly with ContainerD + CRUN + WasmEdge

WebAssembly (Wasm) isn’t just for the browser anymore. It’s conquering the cloud too — and if you're feeling adventurous, let's plug it into container runtimes like containerd, run it with crun, and power up workloads in Kubernetes like a boss. Oh, and yes — we'll even touch on KubeVirt to show Wasm's flexibility in a virtualized world.

🛠️ Step 1: Install WasmEdge (The Wasm Runtime Hero)

Let’s kick things off by installing WasmEdge — a blazing-fast Wasm runtime optimized for cloud-native.

curl -sSf https://raw.githubusercontent.com/WasmEdge/WasmEdge/master/utils/install.sh | bash
source $HOME/.wasmedge/env

✅ Verify Installation

wasmedge --version

Expected output:

wasmedge version 0.13.5

Now that you’re equipped with Wasm superpowers, let’s bring in the container orchestration party.

🧱 Step 2: Set Up ContainerD, CRUN, and Kubernetes

One-liner to install everything you need:

wget -qO- https://raw.githubusercontent.com/sonichigo/wasmedge-demo-example/main/install.sh | bash

This script handles:

• Installing containerd

• Configuring crun as the runtime

• Patching containerd for Wasm support

• Setting up a local Kubernetes cluster

Expected terminal logs include:

> Installing ContainerD and CRUN
<==============================>
...
Local Kubernetes cluster is running. Press Ctrl-C to shut it down.

Boom. That’s your Wasm-ready k8s cluster firing up 🎉

☁️ Step 3: Run a Wasm Container in Kubernetes

Switch into Kubernetes source and set up your config:

cd kubernetes && git checkout v1.22.4

export KUBERNETES_PROVIDER=local

sudo cluster/kubectl.sh config set-cluster local --server=https://localhost:6443 --certificate-authority=/var/run/kubernetes/server-ca.crt
sudo cluster/kubectl.sh config set-credentials myself --client-key=/var/run/kubernetes/client-admin.key --client-certificate=/var/run/kubernetes/client-admin.crt
sudo cluster/kubectl.sh config set-context local --cluster=local --user=myself
sudo cluster/kubectl.sh

Check cluster status:

sudo cluster/kubectl.sh cluster-info

You should see your cluster nodes happily registered.

🌐 Step 4: Deploy a WebAssembly HTTP Service

Time to run a Wasm image in the cluster!

sudo cluster/kubectl.sh run --restart=Never http-server \
  --image=wasmedge/example-wasi-http:latest \
  --annotations="module.wasm.image/variant=compat-smart" \
  --overrides='{"kind":"Pod", "apiVersion":"v1", "spec": {"hostNetwork": true}}'

Then hit it with:

curl -d "name=WasmEdge" -X POST http://127.0.0.1:1234

Expected output:

echo: name=WasmEdge

🥳 Success! You just ran a Wasm container natively in Kubernetes.

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🧪 Bonus: Run This on KubeVirt!

Want to get even fancier? Try this in a KubeVirt virtualized environment. Since KubeVirt can run Kubernetes inside virtual machines, you can embed this Wasm-ready containerd setup inside those VMs — making it super versatile for hybrid environments and edge deployments.

Steps are similar, but inside a KubeVirt VM with Ubuntu or Fedora base image. After that, follow this same guide within that VM and enjoy full Wasm-k8s magic, powered by KubeVirt's virtualization layer.

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3 Ways to Run WASM with OCI & Container Runtimes

There’s more than one way to cook this goose. Here's a breakdown of the 3 main approaches:

🧩 With containerd-shim (runwasi)

• Detects Wasm images via target platform (wasm32)

• Uses runwasi for Wasm, runc for regular containers

• Backed by Docker, Microsoft

• Powering Docker+WASM preview releases

⚙️ Option #2: With crun

• A C-based OCI runtime (from Red Hat)

• Detects Wasm via annotations (module.wasm.image/variant)

• Supports full k8s stack: CRI-O, containerd, Podman, kind, microk8s

🦀 Option #3: With youki

• A Rust-based OCI runtime

• Also annotation-based detection

• Can power CRI-O, containerd, Podman, kind, microk8s, and k8s

All of these can be visualized via their respective integration diagrams — worth including one if you're making this into a slide deck or dev talk!

🔚 Final Thoughts

WebAssembly isn’t the future - it’s the present. With WasmEdge, CRUN, and Kubernetes (even in KubeVirt), we now have the flexibility to run lightweight, fast, and secure applications anywhere. Whether you're targeting the cloud, the edge, or somewhere in between — you’re set up for success.

5 FAQs

1. Why use Wasm instead of Linux containers?

Wasm provides faster startup, smaller size, and better isolation — ideal for microservices and edge computing.

2. Do I need to change my Kubernetes setup to run Wasm?

Nope! With runtimes like crun or youki and proper annotations, it plugs right into your existing Kubernetes flow.

3. What languages can I use to build Wasm apps?

Rust, Go (with TinyGo), C/C++, Python (via Pyodide), and even JavaScript!

4. Can I run Wasm apps alongside Linux containers?

Yes, mixed workloads are totally supported — just annotate your Wasm images and the runtime handles the rest.

5. How does this differ from running containers in Docker?

Docker (via containerd) supports Wasm via runwasi, but this approach goes deeper into Kubernetes and custom runtime integrations using crun/youki.