Unlock the Power of WebAssembly in Cloud-Native Apps

Unlocking the Power of WebAssembly in Kubernetes with Krustlet

As the world of cloud-native development continues to evolve, innovative tools and technologies are emerging to meet the ever-changing demands of modern applications. One such tool that’s gaining attention is Krustlet, a kubelet implementation written in Rust that’s specifically designed to handle WebAssembly (Wasm) workloads. In this article, we’ll delve into the world of Krustlet and explore how to set it up and configure it to work with a Kubernetes cluster to run Wasm workloads.

Prerequisites

Before we dive into the world of Krustlet, make sure you have the following prerequisites in place:

• A running Kubernetes cluster to deploy and manage Krustlet (you can use minikube or Kind to create a local development cluster)
• Docker installed and properly configured on your machine (minikube utilizes Docker as its default container runtime)
• kubectl installed and configured on your device (kubectl is the CLI tool used to interact with Kubernetes clusters, including minikube)

Getting to Know Krustlet

Krustlet, short for Kubernetes Rust kubelet, is an open-source project that provides a Kubernetes kubelet implemented in Rust. As a node agent, Krustlet works in the background to ensure containers are running as expected. It communicates with the Kubernetes API server, receives scheduling instructions, and runs the assigned workloads. What sets Krustlet apart is its ability to handle Wasm workloads, making it ideal for edge computing scenarios.

Understanding the Core Concepts

Wasm is a binary instruction format designed as a portable target for compiling high-level languages such as Rust, C, and C++. It enables applications to run in a web browser at near-native speed, boosting performance over traditional JavaScript execution. However, Wasm’s scope extends beyond the browser. WASI, the system interface for WebAssembly, aims to provide a standardized set of APIs for WebAssembly modules, enabling them to run in various environments, including Kubernetes through Krustlet.

Setting Up Krustlet

To set up Krustlet, you’ll need a Kubernetes cluster and the Krustlet binaries. You can download the Krustlet binaries from the Krustlet GitHub repository or build them yourself. Once you’ve downloaded the right binary for your OS, you can proceed with the installation process by unpacking the downloaded file. After unpacking, you’ll find the Krustlet provider in the directory. To make it easily accessible, move it to a location within your system’s $PATH.

Building a Simple Wasm Module with Rust

To get started, create a new Rust project using the cargo new krustlet_demo command and open it with your chosen text editor. Next, open the ./src/main.rs file and add the following code simulating the work being done:

rust
fn main() {
loop {
println!("Performing recurring task...");
std::thread::sleep(std::time::Duration::from_secs(5));
}
}


This snippet contains a loop that performs a recurring task every 5 seconds. The println! statement represents the recurring task, but you can replace it with any custom logic or operations that need to be repeated regularly.

Publishing a Wasm Artifact to Docker Hub

Next, let’s explore the process for publishing the WebAssembly module to Docker Hub, enabling easy access and deployment for others interested in utilizing your Wasm-powered Rust project. Follow these steps to publish your Wasm artifact to Docker Hub:

1. Install the wasm-to-oci tool, which converts Wasm modules to the OCI format compatible with Docker.
2. Log in to your container registry using the Docker CLI or other available tools provided by the specific container registry.
3. Push the Wasm artifact to Docker Hub using the wasm-to-oci tool.

Deploying with Minikube

To deploy Krustlet using minikube, follow these steps:

1. Start a local Kubernetes cluster using minikube with the following command: minikube start
2. Verify that the cluster is actively running: minikube status
3. Join the cluster with the appropriate permissions using the existing bash script to generate the kubeconfig file and necessary token.
4. Run the Krustlet’s WASI provider with the following command: krustlet-wasi-provider

Verifying Krustlet’s Functionality

To verify Krustlet’s functionality, create a workload.yaml file and update it with the following configuration:

yaml
apiVersion: v1
kind: Pod
metadata:
name: krustlet-demo
spec:
containers:
- name: krustlet-demo
image: <dockerhub-username>/<repository-name>:<tag>
tolerations:
- key: "node.kubernetes.io/disk-type"
operator: "Exists"
effect: "NoSchedule"


Apply the manifest using the following kubectl command: kubectl apply -f workload.yaml

Next, confirm the status of the pod: kubectl get pods

Now, inspect the logs: kubectl logs -f krustlet-demo

With the above logs, your workload is successfully working as expected.

Conclusion

Krustlet provides a compelling way for Rust developers to run WebAssembly workloads in a Kubernetes environment. It extends the versatility of Kubernetes, allowing it to handle more than just container-based applications. For developers invested in Rust and WebAssembly, Krustlet provides an intuitive and efficient way to integrate these technologies into the Kubernetes ecosystem.