Sandbox

How go-faas isolates multi-language user code on Linux and macOS.

Platform Strategy

Production hardening targets Linux. macOS support exists so the API can be developed on Apple hosts.

Linux: systemd Slice

On startup, sandbox.NewSlice() writes ~/.config/systemd/user/go-faas-slice and reloads user systemd:

Each run uses systemd-run --scope --user --quiet --slice=go-faas-slice -- bwrap ....

Linux: Bubblewrap

SandboxCommand (linux build) assembles bwrap flags including:

• Read-only binds for /usr, /lib, /lib64
• Read-only bind of the language wrapper into /wrapper.{py,js,ts}
• --tmpfs /tmp, --proc, --dev
• --unshare-all, --unshare-net (no host network)
• --cap-drop ALL, --die-with-parent, --new-session
• Clean HOME / PATH / TMPDIR / LANG; unset LD_PRELOAD / LD_LIBRARY_PATH
• TypeScript: additional ro-bind of working directory and NODE_PATH to node_modules

Python runs as python3 -u /wrapper.py; JS/TS as node|tsx /wrapper.*.

macOS: sandbox-exec

Darwin build generates a seatbelt profile that:

• Denies by default
• Allows process exec/fork, limited sysctl/mach/signal/IPC
• Allows broad file-read; write only under $HOME
• Allows network (looser than Linux bwrap — development trade-off)

NewSlice() is a no-op on darwin.

Process I/O Contract

Regardless of platform, the child process:

1. Reads one JSON payload on stdin: code + input strings
2. Writes intermediate logs and final JSON result on stdout
3. Writes failures on stderr (SSE path treats stderr as fatal)

Handlers own timeouts via context.WithTimeout around exec.CommandContext.

Dependency Checker

Linux checker.CheckPackage() may install bubblewrap, nodejs, npm, and python3 through apt/dnf/pacman/apk when Node, TypeScript (tsc), esbuild, or Python are missing. Darwin checker is a no-op.

Related

• Architecture
• Core Concepts
• Configuration