Shashank Mohan Jain - WebAssembly for Cloud: A Basic Guide for Wasm-Based Cloud Apps

Somewhere, something incredible is waiting to be known.

Carl Sagan

I start this journey with a quote from the eminent scientist and science communicator Carl Sagan. This short book introduces the amazing world of WebAssembly. The books main theme is to create a simple WebAssembly program from scratch and take it to the cloud. In doing this, youll gain a solid introduction to the valuable features offered by WebAssembly. Consider this book an introduction to WebAssembly and how it is powering browser-based applications and cloud applications. To get the most out of this book, you should have a bit of understanding of cloud fundamentals and basic knowledge of programming languages like Rust, golang and javascript.

I would like to acknowledge Kevin Hoffman, whose work in WebAssembly is an inspiration. Kevin is the creator of the waPC library, which is used in a chapter in the book.

Before introducing WebAssembly, its important to get a brief history of virtualization to better understand the context of WebAssembly.

When VMware started the virtualization revolution, virtual machines were positioned as the unit of computation. This meant that you could create and deploy software compatible with a virtual machine (VM) . The VM-based approach provided great isolation because it introduced a kernel boundary between software and the host on which the workload ran (called a hypervisor ). Although they were secure, VMs were heavy in nature and took time to spin up.

As cloud technology progressed, we saw the advent of container-based virtualization , which was mainly facilitated by structures within the Linux kernel. Containers on the same host shared the Linux kernel but have adequate mechanisms for security, like namespaces, seccomp profiles, and SELinux, which offered multilayered security for containers. In 2018, a new technology called WebAssembly has emerged. It was created by Mozilla and started as a browser-based technology. Since then, developers have employed it on the cloud and server-side apps. WebAssembly allows an extra level of virtualization by running the Wasm computation within a Linux process.

Things began with virtual machines (which are complete operating systems) and then moved to Linux containers (Linux processes protected and isolated by the Linux kernel). Now there is WebAssembly, a computation unit within the Linux process. The goal is to provide a computation unit that can quickly spin up and be suitable for serverless workloads.

WebAssembly (also known as Wasm ) is the new universal bytecode for interoperable compute units. Interoperable means that the compute unit should be able to run on any compatible Wasm runtime. A compute unit is a Wasm module. The basic idea is to have a bytecode format that is universal and standard.

Languages like JavaScript, Rust, Golang, and Java can be compiled to a Wasm-based bytecode. Once this bytecode is generated, it can be executed on any Wasm runtime.

Wasm is a small and efficient stack-based virtual machine that abstracts the target architecture by compiling the code to a universal bytecode representation. Wasm is based on an industry-wide collaborative effort to get a performant and secure close to assembly language. The Bytecode Alliance, set up to create shared implementations of WebAssembly standards, includes major players like Arm , Intel , Google , Microsoft , Mozilla , and Fastly .