Kubernetes + CRI-O

Quick start

The GitHub repo contains scripts and Github Actions for running our example apps on Kubernetes + CRI-O.

• Simple WebAssembly example Quick start | Github Actions | Successful run
• WebAssembly-based HTTP service Quick start | Github Actions | Successful run

In the rest of this section, we will explain the steps in detail. We will assume that you have already installed and configured CRI-O to work with WasmEdge container images.

Install and start Kubernetes

Run the following commands from a terminal window. It sets up Kubernetes for local development.

# Install go
$ wget https://golang.org/dl/go1.17.1.linux-amd64.tar.gz
$ sudo rm -rf /usr/local/go
sudo tar -C /usr/local -xzf go1.17.1.linux-amd64.tar.gz
source /home/${USER}/.profile
# Clone k8s
git clone https://github.com/kubernetes/kubernetes.git
cd kubernetes
git checkout v1.22.2
# Install etcd with hack script in k8s
sudo CGROUP_DRIVER=systemd CONTAINER_RUNTIME=remote CONTAINER_RUNTIME_ENDPOINT='unix:///var/run/crio/crio.sock' ./hack/install-etcd.sh
export PATH="/home/${USER}/kubernetes/third_party/etcd:${PATH}"
sudo cp third_party/etcd/etcd* /usr/local/bin/
# After run the above command, you can find the following files: /usr/local/bin/etcd  /usr/local/bin/etcdctl  /usr/local/bin/etcdutl
# Build and run k8s with CRI-O
sudo apt-get install -y build-essential
sudo CGROUP_DRIVER=systemd CONTAINER_RUNTIME=remote CONTAINER_RUNTIME_ENDPOINT='unix:///var/run/crio/crio.sock' ./hack/local-up-cluster.sh
... ...
Local Kubernetes cluster is running. Press Ctrl-C to shut it down.

Do NOT close your terminal window. Kubernetes is running!

Run WebAssembly container images in Kubernetes

Finally, we can run WebAssembly programs in Kubernetes as containers in pods. In this section, we will start from another terminal window and start using the cluster.

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 config use-context local
sudo cluster/kubectl.sh

Let’s check the status to make sure that the cluster is running.

$ sudo cluster/kubectl.sh cluster-info
# Expected output
Cluster "local" set.
User "myself" set.
Context "local" created.
Switched to context "local".
Kubernetes control plane is running at https://localhost:6443
CoreDNS is running at https://localhost:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.

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 Kubernetes cluster as follows.

sudo cluster/kubectl.sh run -it --rm --restart=Never wasi-demo --image=hydai/wasm-wasi-example:with-wasm-annotation --annotations="module.wasm.image/variant=compat" /wasi_example_main.wasm 50000000

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

Random number: 401583443
Random bytes: [192, 226, 162, 92, 129, 17, 186, 164, 239, 84, 98, 255, 209, 79, 51, 227, 103, 83, 253, 31, 78, 239, 33, 218, 68, 208, 91, 56, 37, 200, 32, 12, 106, 101, 241, 78, 161, 16, 240, 158, 42, 24, 29, 121, 78, 19, 157, 185, 32, 162, 95, 214, 175, 46, 170, 100, 212, 33, 27, 190, 139, 121, 121, 222, 230, 125, 251, 21, 210, 246, 215, 127, 176, 224, 38, 184, 201, 74, 76, 133, 233, 129, 48, 239, 106, 164, 190, 29, 118, 71, 79, 203, 92, 71, 68, 96, 33, 240, 228, 62, 45, 196, 149, 21, 23, 143, 169, 163, 136, 206, 214, 244, 26, 194, 25, 101, 8, 236, 247, 5, 164, 117, 40, 220, 52, 217, 92, 179]
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
pod "wasi-demo-2" deleted

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. Since the HTTP service container requires networking support provided by Kubernetes, we will use a k8s-http_server.yaml file to specify its exact configuration.

apiVersion: v1
kind: Pod
metadata:
  name: http-server
  namespace: default
  annotations:
    module.wasm.image/variant: compat
spec:
  hostNetwork: true
  containers:
  - name: http-server
    image: avengermojo/http_server:with-wasm-annotation
    command: [ "/http_server.wasm" ]
    ports:
    - containerPort: 1234
      protocol: TCP
    livenessProbe:
      tcpSocket:
        port: 1234
      initialDelaySeconds: 3
      periodSeconds: 30

Run the WebAssembly-based image from Docker Hub using the above k8s-http_server.yaml file in the Kubernetes cluster as follows.

sudo ./kubernetes/cluster/kubectl.sh apply -f k8s-http_server.yaml

Use the following command to see the running container applications and their IP addresses. Since we are using hostNetwork in the yaml configuration, the HTTP server image is running on the local network with IP address 127.0.0.1.

$ sudo cluster/kubectl.sh get pod --all-namespaces -o wide
NAMESPACE     NAME                       READY   STATUS             RESTARTS      AGE   IP          NODE        NOMINATED NODE   READINESS GATES
default       http-server                1/1     Running            1 (26s ago)     60s     127.0.0.1   127.0.0.1   <none>           <none>

Now, you can use the curl command to access the HTTP service.

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

That’s it!