Rust and Kubernetes: A Match Made in Heaven

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In recent years, Kubernetes has emerged as the de facto standard for container orchestration. With its ability to manage containerized applications at scale, Kubernetes has become the go-to platform for deploying and managing modern applications. However, as the complexity of applications grows, so too does the need for better tools and technologies to manage them. Enter Rust, a systems programming language that has been gaining popularity in recent years. Rust is well-suited for building reliable and performant systems, making it an ideal choice for building tools and libraries for Kubernetes.

In this blog post, we’ll explore the benefits of using Rust for Kubernetes, and some of the projects that are leveraging Rust to build better tools for Kubernetes.

Why Rust?

Rust is a systems programming language that was created with the goal of providing a safe and performant alternative to C and C++. Rust achieves this goal by providing a modern type system, memory safety, and other features that make it easier to write reliable and performant systems. Rust is designed to be fast and efficient, with a focus on low-level programming and systems-level development. Rust also has a number of other features that make it well-suited for Kubernetes development, including:

Concurrency: Rust has built-in support for concurrency and parallelism, making it well-suited for building distributed systems like Kubernetes.
Performance: Rust’s focus on performance makes it ideal for building high-performance systems like Kubernetes. Rust’s ability to generate code that is as fast as C or C++ means that it can handle the high-performance demands of Kubernetes without sacrificing reliability or safety.
Safety: Rust’s emphasis on memory safety and security makes it an ideal choice for building secure and reliable systems like Kubernetes. With Rust, developers can write code that is less prone to bugs and security vulnerabilities, which is critical in a platform like Kubernetes.
Compatibility: Rust is compatible with a wide range of platforms and architectures, making it well-suited for building tools and libraries that can run on any Kubernetes cluster.

Rust and Kubernetes Projects

Now that we’ve covered some of the benefits of using Rust for Kubernetes development, let’s take a look at some of the projects that are leveraging Rust to build better tools and libraries for Kubernetes.

Krator

Krator is a Kubernetes controller runtime that is written entirely in Rust. Krator provides a number of features that make it well-suited for Kubernetes development, including a simple and intuitive API, built-in metrics, and support for custom resource definitions. Krator is designed to be lightweight and efficient, making it ideal for running in resource-constrained environments like edge clusters.
Krator is an open-source Kubernetes operator written in Rust. It allows you to easily define and manage Kubernetes resources through Rust code, making it a powerful tool for building and managing Kubernetes applications.

Here’s an example of using Krator to define a custom Kubernetes resource:

use kube::{
    api::{Api, DynamicObject},
    Client,
};
use krator::{ObjectState, Operator, OperatorRuntime};
use schemars::JsonSchema;
use serde::{Deserialize, Serialize};
use std::{collections::HashMap, sync::Arc};

#[derive(Clone, Debug, PartialEq, JsonSchema, Serialize, Deserialize)]
struct MyResourceSpec {
    count: i32,
}

#[derive(Clone, Debug, PartialEq, Default, JsonSchema, Serialize, Deserialize)]
struct MyResourceStatus {
    count: i32,
}

#[derive(Clone, Debug, PartialEq, JsonSchema, Serialize, Deserialize)]
struct MyResource {
    spec: MyResourceSpec,
    status: Option<MyResourceStatus>,
}

impl ObjectState for MyResource {
    type Status = MyResourceStatus;
    type Manifest = MyResource;

    fn status(&self) -> Option<Self::Status> {
        self.status.clone()
    }

    fn manifest(&self) -> Self::Manifest {
        self.clone()
    }
}

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Set up a Kubernetes client
    let client = Client::try_default().await?;

    // Set up an API for our custom resource
    let my_resource_api = Api::<DynamicObject>::all_with(client.clone(), "myresources");

    // Set up the Krator operator
    let operator = Operator::new(client, my_resource_api)
        .owns::<MyResource>()
        .run(MyResource::default(), MyResourceStatus::default());

    // Start the operator runtime
    let mut runtime = OperatorRuntime::new(operator);
    runtime.start().await?;
    Ok(())
}

In this example, we define a custom Kubernetes resource called MyResource, which has a spec field of type MyResourceSpec and an optional status field of type MyResourceStatus. We then define the ObjectState trait for MyResource, which allows us to define how the resource should be represented in Kubernetes.

We then set up a Kubernetes client and an API for our custom resource, and use them to set up a Krator operator. Finally, we start the Krator operator runtime and let it run.

This is just a simple example, but Krator can be used to define and manage much more complex Kubernetes resources and applications.

Krustlet

Krustlet is a Kubernetes Kubelet implementation that is written entirely in Rust. Krustlet is designed to run WebAssembly workloads natively on Kubernetes, making it an ideal choice for developers who want to build serverless applications using Kubernetes. Krustlet provides a number of features that make it well-suited for Kubernetes development, including a lightweight and efficient runtime, support for multiple architectures, and a flexible plugin architecture.

Here’s an example of using Krustlet to run a simple Rust function as a serverless function:

use kubelet::{
    config::Config,
    container::{Container, ContainerBuilder},
    pod::{Pod, PodBuilder, Status},
    provider::Provider,
};
use std::{collections::HashMap, sync::Arc};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Set up Krustlet configuration
    let config = Config::new_from_flags(env!("CARGO_PKG_VERSION")).await?;

    // Define a simple Rust function to be run as a serverless function
    async fn hello_serverless() -> String {
        "Hello, Krustlet!".to_string()
    }

    // Set up the container to run the Rust function
    let container = ContainerBuilder::new("hello-serverless".to_string(), "rust".to_string())
        .image("rust:latest".to_string())
        .command(vec!["bash".to_string(), "-c".to_string(), "while true; do sleep 30; done".to_string()])
        .add_env("TARGET", "x86_64-unknown-linux-musl".to_string())
        .add_env("PROFILE", "release".to_string())
        .add_env("RUSTFLAGS", "-C target-feature=-crt-static".to_string())
        .add_env("CARGO_INCREMENTAL", "0".to_string())
        .add_env("CARGO_BUILD_TARGET", "wasm32-wasi".to_string())
        .build()
        .unwrap();

    // Set up the pod to contain the container
    let pod = PodBuilder::new("hello-serverless".to_string())
        .containers(vec![container])
        .node_name(config.node_name.clone())
        .build()
        .unwrap();

    // Create a provider using Krustlet and the pod configuration
    let provider = Provider::new(Arc::new(config.clone()));

    // Start the provider and run the pod
    let pod_handle = provider.create_pod(pod).await?;
    loop {
        let status = provider.pod_status(&pod_handle).await?;
        if let Status::Succeeded(_) = status {
            let logs = provider.logs(&pod_handle, &container.name()).await?;
            println!("Logs:\n{}", logs);
            let output = provider
                .exec(&pod_handle, &container.name(), vec!["/bin/sh".to_string(), "-c".to_string(), "cat /tmp/result".to_string()])
                .await?;
            println!("Output:\n{}", output);
            break;
        } else if let Status::Failed(_) = status {
            let logs = provider.logs(&pod_handle, &container.name()).await?;
            println!("Logs:\n{}", logs);
            break;
        }
    }

    Ok(())
}

In this example, we define a simple Rust function called hello_serverless() that returns a string. We then set up a container to run the Rust function as a serverless function, and a pod to contain the container. Finally, we create a Krustlet provider and use it to run the pod, retrieve the logs, and display the output of the Rust function. This is just one example of the many ways that Krustlet can be used to run serverless functions in Rust.

Kube-rs

Kube-rs is a Rust library for working with the Kubernetes API. Kube-rs provides a simple and intuitive API for working with Kubernetes resources, making it easy to build Kubernetes controllers and other tools in Rust. Kube-rs is designed to be fast and efficient, with a focus on performance and scalability.

Here’s an example of using the Kube-rs library to create a Kubernetes pod:

use kube::api::{Api, PostParams};
use kube::Client;
use serde_json::json;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Create a Kubernetes client
    let client = Client::try_default().await?;

    // Create a new pod object
    let pod = json!({
        "apiVersion": "v1",
        "kind": "Pod",
        "metadata": {
            "name": "example-pod"
        },
        "spec": {
            "containers": [{
                "name": "example-container",
                "image": "nginx"
            }]
        }
    });

    // Create a Kubernetes API object for the pods resource
    let pods: Api<Pod> = Api::namespaced(client, "default");

    // Create the pod
    let post_params = PostParams::default();
    let result = pods.create(&post_params, serde_json::to_vec(&pod)?).await?;

    println!("Created pod {:?}", result);

    Ok(())
}

This code creates a Kubernetes client using the Kube-rs library, creates a new pod object using JSON, creates a Kubernetes API object for the pods resource, and then creates the pod using the API object. This is just one example of the many ways that Rust can be used to interact with Kubernetes resources.

Conclusion

Rust and Kubernetes are both technologies that have gained significant momentum in recent years. With its focus on reliability, performance, and safety, Rust is well-suited for building tools and libraries for Kubernetes. Projects like Krator, Krustlet, and Kube-rs are leveraging Rust to build better tools and libraries for Kubernetes, providing developers with new ways to build and manage modern applications at scale.