WASM sandboxes use a host-mediated model: the API server stays in sandboxd, while each sandbox runs inside a dedicated worker subprocess speaking IPC over a Unix socket.

Components

sandboxd (service layer)
  └─ internal/runtime/wasm.Driver
       ├─ pkg/wasmmod resolver (module cache)
       ├─ pkg/wasm/worker supervisor
       └─ toolbox reverse proxy (files / exec)

Checkpoint format

Passivation writes a mem.snap directory:

• config.json — engine metadata, clone generation, module digest
• memory.zstd, globals.cbor, wasi-state.cbor — guest state

Durable sandboxes push the directory to AOCR at:

cluster/<cluster-id>/wasm-checkpoints/<sandbox-id>:latest

Lifecycle

1. Create — resolve module, start or acquire warm worker, instantiate, invoke entrypoint.
2. Passivate — checkpoint live guest, stop worker, release admission.
3. Rehydrate — restore from local mem.snap (pull from AOCR first when durable and missing).
4. Failover — cluster owner calls RecreateSandbox; durable WASM pulls checkpoint then rehydrates.

Configuration

Variable	Purpose
SB_ENABLE_WASM	Master gate
SB_WASM_MODULES_DIR	Module + checkpoint cache root
SB_WASM_CHECKPOINT_INTERVAL	Optional periodic boundary checkpoint
SB_WASM_DURABLE_PUSH_INTERVAL	Retry AOCR push for durable rows
SB_SNAPSHOT_PUSH_ENABLED	Enables AOCR push/pull credentials

Operations

See the WASM runtime health runbook for failure modes and log signatures.