Server-side WebAssembly applications need filesystem access, but current options are limited. Host filesystem access breaks portability and sandboxing. wasi-vfs is read-only and targets Preview 1. wasi-virt supports Preview 2 but remains read-only and single-application only.
We present a virtual filesystem built on WASI Preview 2 and the Component Model that supports read/write, multi-app sharing, dynamic attachment via RPC, and optional S3 persistence. The stack uses open-source tooling from the Bytecode Alliance: wasmtime, wac, and wit-bindgen.
The talk walks through our architecture: an inode-based in-memory filesystem exposed through custom adapters implementing wasi:filesystem, composed at build time with wac plug. We then separate the filesystem into a standalone server, add RPC for runtime attachment without recompilation, and layer S3 persistence for durability. Each stage is demonstrated live.
We close with lessons learned and tradeoffs between build-time composition and runtime RPC. No deep Wasm expertise is assumed. This talk is for developers building Wasm platforms, those exploring the Component Model, and anyone curious about filesystem virtualization in WebAssembly.