Trigger and scope

Trigger on: Fastly Compute, Compute@Edge, WASM on Fastly, fastlike, XQD ABI, Compute request lifecycle, 508 loop detection, backend subrequests, body streaming, profiling a local Compute app, embedding a Fastly Compute runtime in Go code, or any question about how Compute platform primitives work internally (caching, KV stores, edge rate limiting, ACLs, geolocation, secret stores, config stores, dictionaries, logging, dynamic backends, request collapsing, async I/O).

Do NOT use for: Fastly VCL (use falco), Fastly CLI/API (use fastly-cli or fastly), Viceroy, CDN comparison, WAF, Terraform, cache purging via API, or Fastly logging/stats configuration.

Fastlike — Local Compute Runtime & Reference

Fastlike is a Go implementation of the Fastly Compute ABI. It runs compiled WebAssembly programs locally, implementing the same 249+ host functions that Fastly's production Compute platform provides: backends, dictionaries, KV stores, caching, geolocation, rate limiting, ACLs, secret stores, and more.

Equally important, the fastlike source code is the most complete programmatic specification of how Fastly Compute works — its ABI implementations document every platform primitive, request lifecycle detail, and data structure as executable code.

Fastlike documentation: https://github.com/avidal/fastlike

Source Code as Compute Reference

When you have access to the fastlike source code locally (default: ~/src/fastlike), use these paths to answer specific Compute questions:

For a comprehensive guide, see understanding-compute-from-source.md.

Install from Source

Requires Go 1.24+.

# Clone and build
git clone https://github.com/avidal/fastlike.git ~/src/fastlike
cd ~/src/fastlike
make build        # Creates bin/fastlike

# Or install to GOPATH/bin
make install

# Or install directly
go install fastlike.dev/cmd/fastlike@latest

Quick Start

# Minimal: WASM + single backend. The wasm path is positional.
bin/fastlike -backend localhost:8000 app.wasm

Flags can appear on either side of the wasm path.

On macOS, avoid binding to port 5000 — the AirTunes/AirPlay Receiver listens there by default and will steal the connection. Pick another port (e.g. -bind localhost:8000) or disable the AirPlay Receiver in System Settings.

Fastlike vs Viceroy

When to use Fastlike: Non-Rust Compute apps, want custom geo data, need hot reload, debugging. When to use Viceroy: Rust Compute apps with cargo-nextest, Component Model projects, using fastly compute serve.

Common Configurations

With named backends:

bin/fastlike \
  -backend api=api.example.com:8080 \
  -backend cache=redis:6379 \
  -backend localhost:8000 \
  app.wasm

Development mode with hot-reload:

bin/fastlike -backend localhost:8000 -reload -v 2 app.wasm

Send SIGHUP to reload the WASM without restarting.

With the built-in profiler:

bin/fastlike -backend localhost:8000 -profile-ui localhost:6060 app.wasm

Open http://localhost:6060/ for the trace index. Each request lands as /r/{id} (HTML) or /r/{id}.json (canonical native JSON; also .chrome.json, .firefox.json, .pprof). Add -profile deep for body byte / cache outcome / header / wasm heap metrics. Non-loopback -profile-ui requires -profile-auth TOKEN (or explicit -profile-insecure-ui). See profiling.md.

Full configuration:

bin/fastlike \
  -bind 0.0.0.0:5000 \
  -backend localhost:8000 \
  -dictionary config=./config.json \
  -kv store=./data.json \
  -config-store settings=./settings.json \
  -secret-store secrets=./secrets.json \
  -acl blocklist=./acl.json \
  -logger output=./logs.txt \
  -geo ./geodata.json \
  -compliance-region us-eu \
  -v 2 \
  -reload \
  app.wasm

Required Arguments

Optional Flags

References