Beyond Kubernetes: Exploring WebAssembly for Cloud

• 15/5/2024
• 6-minute read

While containers and Kubernetes have revolutionized how we build, deploy, and scale cloud-native applications, a new contender is rapidly gaining traction in the industry: WebAssembly (Wasm). Originally designed for the browser, WebAssembly has evolved into a compelling runtime environment for server-side applications, bringing unique advantages in portability, security, and performance. This article explores how WebAssembly is positioning itself as both a complement and, in some cases, an alternative to traditional containerization in cloud environments.

The Limitations of Traditional Containerization

Containers have become the standard deployment unit for cloud-native applications, offering significant improvements over traditional virtual machines. However, they come with certain limitations:

These limitations become increasingly apparent in certain use cases like edge computing, serverless functions, and multi-tenant environments where resource efficiency and security are paramount.

What is WebAssembly?

WebAssembly (Wasm) is a binary instruction format designed as a portable compilation target for high-level languages. Initially created to enable near-native performance for web applications, Wasm has four core principles:

1. Fast: Executes at near-native speed
2. Safe: Runs in a memory-safe, sandboxed environment
3. Portable: Runs on multiple platforms without modification
4. Compact: Has a binary format that’s compact and efficiently loadable

// Simple Rust function compiled to WebAssembly
#[no_mangle]
pub extern "C" fn add(a: i32, b: i32) -> i32 {
    a + b
}

The code above shows a simple Rust function that can be compiled to WebAssembly and executed in any Wasm runtime, whether in a browser or on the server.

Wasm vs. Containers: A Comparison

WebAssembly and containers serve similar purposes but take fundamentally different approaches:

Key Benefits of WebAssembly for Cloud Native

Portability

WebAssembly modules are platform-agnostic, allowing them to run consistently across different environments without modification:

• Deploy the same binary from edge to cloud
• Run on any CPU architecture without rebuilding
• Execute in browsers, servers, IoT devices, and more

Security Sandbox

WebAssembly provides a defense-in-depth security model:

• Memory isolation: Each module has its own linear memory that other modules cannot access directly
• Capability-based security: Explicit imports for system resources
• No system calls: Cannot access system resources without explicit permissions

Small Footprint and Fast Startup

WebAssembly modules are:

• Typically measured in kilobytes (vs. megabytes for containers)
• Capable of cold starts in milliseconds (vs. seconds for containers)
• Significantly more resource-efficient than containers

This makes Wasm particularly suitable for environments where resources are constrained or where rapid scaling is essential.

Language-Agnostic

WebAssembly supports multiple programming languages, including but not limited to:

• Rust
• C/C++
• AssemblyScript (TypeScript-like)
• Go
• Python (via interpreters)
• JavaScript (via runtimes)

Use Cases for WebAssembly in Cloud Environments

Edge Computing

Edge computing demands lightweight, secure, and portable runtime environments—areas where WebAssembly excels:

• Content delivery networks: Dynamic edge functions
• IoT gateways: Processing data close to the source
• Edge AI: Running machine learning inference at the edge

Serverless Functions

WebAssembly addresses key challenges in serverless computing:

• Cold start latency: Millisecond startup times vs. seconds for container-based functions
• Multi-tenancy: Strong isolation between functions
• Resource efficiency: Lower memory and CPU overhead
• Billing precision: Less wasted resources, more accurate billing

Plugin Systems

WebAssembly enables secure, dynamic extension of applications:

• SaaS platforms: Customer-specific customizations
• Content management systems: Custom content processing
• Data processing pipelines: Customizable transformation stages

Tools and Frameworks

The WebAssembly ecosystem is rapidly evolving, with several frameworks and tools emerging for cloud-native development:

Runtimes

• Wasmtime: A standalone WebAssembly runtime
• WasmEdge: A lightweight, high-performance WebAssembly runtime
• Wasmer: A universal WebAssembly runtime supporting multiple backends

Orchestration Tools

• SpinKube: Kubernetes extension for managing WebAssembly workloads
• Krustlet: Kubernetes Kubelet implementation for running WebAssembly
• Fermyon Spin: A framework for building and running WebAssembly microservices

Development Frameworks

• Fermyon Spin: A developer-friendly framework for building WebAssembly microservices
• WAGI (WebAssembly Gateway Interface): CGI-like interface for WebAssembly
• Extism: Framework for building and using WebAssembly plugins

Implementation Example: A Simple WebAssembly Service

Here’s a simplified example of a HTTP service written in Rust and compiled to WebAssembly using the Spin framework:

use spin_sdk::http::{Request, Response};
use spin_sdk::http_component;

/// A simple Spin HTTP component.
#[http_component]
fn handle_request(req: Request) -> Response {
    println!("Received request to {}", req.uri());
    
    Response::builder()
        .status(200)
        .header("content-type", "text/plain")
        .body(Some("Hello from WebAssembly!".into()))
        .build()
}

This service can be compiled to a WebAssembly module and deployed to any Spin-compatible environment, from a developer’s laptop to a cloud platform, with consistent behavior.

Challenges and Future Outlook

While WebAssembly shows tremendous promise for cloud-native applications, several challenges remain:

Current Limitations

• Standard library access: Limited compared to traditional runtimes
• Ecosystem immaturity: Fewer tools, libraries, and best practices
• Performance overhead: For certain workloads, especially I/O-bound ones
• Development complexity: Additional compilation step and platform constraints

Evolving Standards

The WebAssembly community is actively addressing these limitations through new standards:

• WASI (WebAssembly System Interface): Standardized system interface for WebAssembly
• Component Model: Facilitating composition of WebAssembly modules
• Interface Types: Better interoperability between languages
• Garbage Collection: Native support for languages requiring garbage collection
• Threading: Standardized multi-threading support

WebAssembly and Kubernetes: Coexistence Strategy

Rather than viewing WebAssembly as a replacement for Kubernetes, many organizations are adopting a hybrid approach:

• Kubernetes for stateful, long-running services
• WebAssembly for stateless, event-driven functions
• Integration via projects like Krustlet and SpinKube

This approach leverages the strengths of both technologies while mitigating their respective weaknesses.

Conclusion

WebAssembly is emerging as a compelling runtime for cloud-native applications, offering significant advantages in portability, security, and efficiency compared to traditional containerization. While it’s unlikely to replace Kubernetes in the short term, WebAssembly is carving out its own niche in areas like edge computing, serverless functions, and plugin systems where its unique characteristics provide tangible benefits.

As the ecosystem matures and standards evolve, we can expect WebAssembly to play an increasingly important role in the cloud-native landscape, complementing and extending existing container-based architectures. Forward-thinking organizations should begin exploring WebAssembly now to understand its potential benefits and limitations in their specific contexts.

Further Reading

• WebAssembly Official Website
• WebAssembly System Interface (WASI)
• WebAssembly vs. Containers: Which Is Right for Your Workload?
• Krustlet: Kubernetes and WebAssembly
• Fermyon Spin: WebAssembly Microservices Framework