Wasm runtime

Edgelet runs Wasm workloads on linux when containerEngine: edgelet. Workloads use platform: wasi/wasm and a RuntimeClass handler. Docker and Podman engines do not support RuntimeClass on Edgelet.

Prerequisites

Requirement	Detail
Platform	linux only
Engine	containerEngine: edgelet
Shim binary	Handler-specific containerd-shim-* on PATH (see table below)
RuntimeClass	Deployed on the node before scheduling a Wasm microservice

potctl can stage Wasm shims during Edgelet node install when package.wasm is set on the Agent manifest. Native linux install only; skipped for deploymentType: container and for containerEngine: podman.

RuntimeClass

Register handlers with EdgeletAPI deploy manifests (apiVersion: edgelet.iofog.org/v1). Each metadata.name is the value you set on spec.container.runtime in Controller YAML.

apiVersion: edgelet.iofog.org/v1
kind: RuntimeClass
metadata:
  name: edgelet-wasmtime
handler: edgelet-wasmtime

Apply on the node:

edgelet deploy -f runtimeclass-edgelet-wasmtime.yaml
edgelet deploy -f runtimeclass-edgelet-wasmtime.yaml --dry-run

edgelet-wasmtime is the Datasance wasmtime shim (containerd-shim-edgelet-v2). It is not the same as containerEngine: edgelet (the embedded OCI engine).

Supported handlers

Handler	Shim binary (primary)	Notes
edgelet-wasmtime	containerd-shim-edgelet-v2	Datasance shim; recommended for generic WASI images
spin	containerd-shim-spin-v2	Spin framework workloads
wasmtime	containerd-shim-wasmtime-v2	Upstream wasmtime shim
wasmedge	containerd-shim-wasmedge-v2	WasmEdge shim
wasmer	containerd-shim-wasmer-v2	Wasmer shim
slight	containerd-shim-slight-v2	Slight runtime
lunatic	containerd-shim-lunatic-v2	Lunatic runtime
wws	containerd-shim-wws-v2	Wasmer WASIX (wws)

Edgelet discovers shims from PATH. If the shim is missing, deploy fails with a clear error when the workload starts.

Pin a Wasm microservice

Controller YAML uses apiVersion: {API_VERSION}. Set spec.container.platform to wasi/wasm and spec.container.runtime to the RuntimeClass metadata.name (not containerEngine).

Microservice (edgelet-wasmtime)

apiVersion: datasance.com/v3
kind: Microservice
metadata:
name: wasm2
spec:
name: wasm2
agent:
  name: edge-1
images:
  registry: 1
  amd64: ghcr.io/containerd/runwasi/wasi-demo-app:latest
  arm64: ghcr.io/containerd/runwasi/wasi-demo-app:latest
container:
  platform: wasi/wasm
  runtime: edgelet-wasmtime
  ports:
    - internal: 8080
      external: 8081
      protocol: tcp
application: wasm

Spin example (runtime: spin):

Application excerpt (spin)

apiVersion: datasance.com/v3
kind: Application
metadata:
name: wasm
spec:
microservices:
  - name: wasm
    agent:
      name: controller-1
    images:
      registry: 1
      amd64: ghcr.io/spinframework/containerd-shim-spin/examples/spin-rust-hello:v0.22.0
      arm64: ghcr.io/spinframework/containerd-shim-spin/examples/spin-rust-hello:v0.22.0
    container:
      platform: wasi/wasm
      runtime: spin
      ports:
        - internal: 80
          external: 8080
          protocol: tcp
      commands:
        - "/"

Deploy the application with potctl after the RuntimeClass exists on the target Edgelet node.

Operator install (optional)

When provisioning an Edgelet node, potctl can install configured Wasm handlers and apply matching RuntimeClass manifests. Set package.wasm on the Agent kind with handler keys (for example edgelet-wasmtime, spin). See Setup Edgelet Nodes.

Troubleshooting

Symptom	Check
runtimeclass is supported only when containerEngine=edgelet	Set containerEngine: edgelet on linux
Workload stuck or shim error	which containerd-shim-edgelet-v2 (or handler-specific shim); redeploy RuntimeClass
Handler not found	edgelet deploy -f runtimeclass.yaml --dry-run; confirm metadata.name matches spec.container.runtime

See also

• Container engines - engine matrix and RuntimeClass overview
• EdgeletAPI v1 - deploy endpoints for RuntimeClass
• edgelet deploy - apply manifests on the node

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