Viceroy is Fastly's official local testing environment for Compute applications. It emulates the Fastly Compute platform, allowing you to develop and test WASM services locally.
Viceroy documentation: https://github.com/fastly/Viceroy
Common Gotchas
- Dictionaries and ConfigStores are both supported but configured differently in
fastly.toml. Dictionaries go under[local_server.dictionaries]as inline key-value maps or JSON files. ConfigStores go under[local_server.config_stores]. fastly.tomlmust have a[local_server]section. Without it, Viceroy won't know about your backends, stores, or other local overrides. Every backend your app calls must be listed under[local_server.backends].- Default port is 7676, not 5000 (which is Fastlike's default). Access your app at
http://127.0.0.1:7676. - Backends should point to local servers when developing locally. Avoid proxying to remote production origins to prevent accidentally leaking request data.
Quick Start
# Install Viceroy
cargo install --locked viceroy
fastly compute build
Start local server (default: 127.0.0.1:7676)viceroy -C fastly.toml bin/main.wasm
Or use the Fastly CLI wrapperfastly compute serve
## References
| Topic | File | Use when... |
| ------ | --------------------------------------------------------------- | ------------------------------------------------------------------------------ |
| Serve | [fastly-compute-serve.md](references/fastly-compute-serve.md) | Starting local dev server, profiling, advanced server options |
| Config | [fastly-compute-config.md](references/fastly-compute-config.md) | Configuring fastly.toml backends, stores, geolocation, device detection, ACLs |
| Test | [fastly-compute-test.md](references/fastly-compute-test.md) | Running Rust unit tests with cargo-nextest, writing tests for Compute services |
| Adapt | [fastly-compute-adapt.md](references/fastly-compute-adapt.md) | Converting core WASM modules to Component Model, custom build pipelines |