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K3s

K3s is a lightweight, certified Kubernetes distribution designed for resource-constrained environments such as edge, IoT, and CI/CD. It bundles containerd as the default container runtime and can automatically detect WebAssembly runtimes like WasmEdge.

備註

This guide is based on containerd + runwasi (containerd-shim-wasmedge).

Prerequisites​

  • A Linux machine (x86_64 or aarch64) with systemd
  • Root or sudo access

Install WasmEdge​

Use the simple install script to install WasmEdge on your node.

curl -sSf https://raw.githubusercontent.com/WasmEdge/WasmEdge/master/utils/install.sh | bash

Install the containerd-shim-wasmedge​

K3s looks for the containerd-shim-wasmedge-v1 binary in the system PATH. You can install it from a pre-built release binary or build it from source.

Option A: Pre-built binary​

Download the latest release from the runwasi releases page and install it.

# Detect architecture and download the appropriate binary
ARCH=$(uname -m) # x86_64 or aarch64
wget https://github.com/containerd/runwasi/releases/download/containerd-shim-wasmedge%2Fv0.6.0/containerd-shim-wasmedge-${ARCH}-linux-musl.tar.gz
tar xzf containerd-shim-wasmedge-${ARCH}-linux-musl.tar.gz
sudo install -m 755 containerd-shim-wasmedge-v1 /usr/local/bin/

Option B: Build from source​

Make sure you have Rust installed, then build the shim from the runwasi project.

git clone https://github.com/containerd/runwasi.git
cd runwasi
./scripts/setup-linux.sh
make build-wasmedge
INSTALL="sudo install" LN="sudo ln -sf" make install-wasmedge

Install and start K3s​

Install K3s after the shim binary is in place, so that K3s can detect the WasmEdge runtime at startup.

curl -sfL https://get.k3s.io | sh -

K3s will automatically detect containerd-shim-wasmedge-v1 in the system PATH and create a corresponding Kubernetes RuntimeClass named wasmedge.

Verify that K3s is running and the RuntimeClass exists:

sudo kubectl get nodes
sudo kubectl get runtimeclass

Expected output:

$ sudo kubectl get nodes
NAME     STATUS   ROLES           AGE   VERSION
ubuntu   Ready    control-plane   45s   v1.34.6+k3s1

$ sudo kubectl get runtimeclass
NAME                  HANDLER               AGE
crun                  crun                  45s
lunatic               lunatic               45s
nvidia                nvidia                45s
nvidia-experimental   nvidia-experimental   45s
slight                slight                45s
spin                  spin                  45s
wasmedge              wasmedge              45s
wasmer                wasmer                45s
wasmtime              wasmtime              45s
wws                   wws                   45s

Make sure wasmedge is in the list.

備註

If the wasmedge RuntimeClass does not appear, make sure the containerd-shim-wasmedge-v1 binary is in a directory listed in the K3s service's PATH (e.g., /usr/local/bin), then restart K3s with sudo systemctl restart k3s.

Run a simple WebAssembly app​

A separate article explains how to compile, package, and publish a simple WebAssembly WASI program as a container image to Docker Hub. Run the WebAssembly-based image from Docker Hub in the K3s cluster as follows.

sudo kubectl run --restart=Never wasi-demo \
  --image=wasmedge/example-wasi:latest \
  --overrides='{"kind":"Pod","apiVersion":"v1","spec":{"runtimeClassName":"wasmedge"}}' \
  -- /wasi_example_main.wasm 50000000

Check the pod status and view the output:

sudo kubectl get pod wasi-demo
sudo kubectl logs wasi-demo

The output from the containerized application is printed into the console.

$ sudo kubectl get pod wasi-demo
NAME        READY   STATUS      RESTARTS   AGE
wasi-demo   0/1     Completed   0          7s

$ sudo kubectl logs wasi-demo
Random number: -817406905
Random bytes: [7, 7, 147, 202, 106, 102, 198, 6, 42, 39, 198, 92, 59, 247, 54, 99, 249, 117, 113, 143, 240, 85, 226, 102, 44, 165, 66, 251, 220, 107, 106, 70, 168, 144, 114, 113, 77, 132, 114, 33, 155, 254, 169, 196, 218, 119, 171, 145, 106, 36, 205, 130, 43, 208, 152, 127, 60, 57, 26, 160, 178, 75, 3, 215, 98, 32, 223, 67, 176, 35, 182, 141, 2, 190, 15, 72, 167, 44, 46, 148, 240, 1, 110, 148, 19, 134, 182, 21, 127, 141, 106, 65, 27, 84, 121, 217, 171, 36, 88, 47, 197, 96, 193, 102, 143, 105, 67, 77, 40, 187, 40, 151, 60, 140, 238, 143, 8, 89, 129, 117, 103, 157, 102, 34, 65, 5, 195, 246]
Printed from wasi: This is from a main function
This is from a main function
The env vars are as follows.
The args are as follows.
/wasi_example_main.wasm
50000000
File content is This is in a file

Clean up the pod after verifying:

sudo kubectl delete pod wasi-demo

Run a WebAssembly-based HTTP service​

A separate article explains how to compile, package, and publish a simple WebAssembly HTTP service application as a container image to Docker Hub. Create a deployment using a YAML file:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: http-server
spec:
  replicas: 1
  selector:
    matchLabels:
      app: http-server
  template:
    metadata:
      labels:
        app: http-server
    spec:
      runtimeClassName: wasmedge
      containers:
        - name: http-server
          image: wasmedge/example-wasi-http:latest
          ports:
            - containerPort: 1234
              protocol: TCP
---
apiVersion: v1
kind: Service
metadata:
  name: http-server
spec:
  type: NodePort
  selector:
    app: http-server
  ports:
    - port: 1234
      targetPort: 1234

Save the above as k3s-http-server.yaml and apply it:

sudo kubectl apply -f k3s-http-server.yaml

Wait for the pod to be ready, then get the NodePort:

sudo kubectl get svc http-server

Access the HTTP service using the NodePort:

curl -d "name=WasmEdge" -X POST http://localhost:<NodePort>
echo: name=WasmEdge

Clean up the deployment and service after verifying:

sudo kubectl delete -f k3s-http-server.yaml

That's it!