Fuse

A control plane for agents — deploy Firecracker microVMs anywhere, with one script.

Fuse lets you stand up isolated microVMs on your own hosts and drive their full lifecycle (provision → running → drain → destroy) through a REST API. It's the orchestration layer agents need for sandboxed compute — scheduling, snapshots, host management, and live event streams — built on Firecracker and entirely open source.

The hard part of Firecracker has always been getting it running: the host setup, the in-guest agent, building a rootfs. Fuse collapses all of that into a single script — one command brings up a host with the agent installed and a rootfs baked and ready.

What you get out of the box

• One-script Firecracker setup — host, agent, and a baked rootfs, ready to boot.
• Scheduling across hosts — register hosts, and Fuse places microVMs for you.
• Full VM lifecycle — provision → running → drain → destroy, tracked and reconciled.
• Snapshots — capture a running microVM and restore from it.
• Live event streams — tail a microVM's events over SSE.
• Durable state — backed by Postgres (or in-memory for local runs).
• Per-VM secrets — credentials generated per microVM, tokens encrypted at rest.
• REST API + Prometheus metrics — drive everything over HTTP; observe it out of the box.

Firecracker, made simple

Getting Firecracker production-ready is normally a slog: install the binary, fetch a kernel, build a rootfs, customize it, wire up networking, expose a control port. Fuse ships that whole toolchain as a set of idempotent scripts in host-agent/, so a host goes from bare to bootable in a few commands:

cd host-agent
./fc-install.sh          # firecracker binary + kernel + base rootfs
./fc-bake-rootfs.sh      # build your guest rootfs
./fc-agent.sh start      # start the host agent — prints FIRECRACKER_BASE_URL + FIRECRACKER_TOKEN

Copy those two printed values into Fuse's config and you're scheduling microVMs. Every script is idempotent and safe to re-run. By default the rootfs ships with fused, our reference in-guest agent — but the rootfs is yours to customize (more on the agent below).

Concepts

Environments

An environment is a single Firecracker microVM and the task running inside it. You create one with a spec (CPU/memory), an optional manifest and secrets, and an optional startup script; Fuse picks a host, boots the VM, uploads your files, starts the in-guest agent, and tracks it through provision → running → drain → destroy. A background reconcile loop catches orphans and stuck VMs.

Method	Path	Purpose
POST	/v1/environments	Create a microVM for a task
GET	/v1/environments	List environments
GET	/v1/environments/{id}	Get one environment
POST	/v1/environments/{id}?action=drain	Gracefully drain (or rotate-token)
DELETE	/v1/environments/{id}	Destroy the microVM

Hosts

A host is a machine running the Firecracker host agent. Register your hosts and Fuse schedules microVMs across them. You can cordon a host to stop new placements (e.g. before maintenance) and uncordon it to resume.

Method	Path	Purpose
POST	/v1/hosts	Register a host
GET	/v1/hosts	List hosts
GET	/v1/hosts/{id}	Get one host
POST	/v1/hosts/{id}?action=cordon	Cordon (or uncordon)
DELETE	/v1/hosts/{id}	Remove a host

Snapshots

A snapshot captures a running microVM's state so you can restore from it later — useful for fast cold-starts, checkpointing long tasks, or branching from a known-good point. Snapshots are persisted records and can carry a comment, retention, and metadata.

Method	Path	Purpose
POST	/v1/environments/{id}/snapshots	Snapshot a running microVM
GET	/v1/snapshots	List snapshots
GET	/v1/snapshots/{id}	Get one snapshot
POST	/v1/snapshots/{id}?action=restore	Restore a microVM from a snapshot
DELETE	/v1/snapshots/{id}	Delete a snapshot

Logs & events

Each environment exposes a live event stream over Server-Sent Events — tail state transitions and activity as they happen, no polling.

Method	Path	Purpose
GET	/v1/environments/{id}/events	Stream environment events (SSE)

Quickstart

# Build
go build -o bin/fuse ./cmd/orchestrator

# Run against a Firecracker host (see host-agent/ to bring one up)
export FIRECRACKER_BASE_URL=http://<host>:<port>
export FIRECRACKER_TOKEN=<token>
export TOKEN_ENCRYPTION_KEY=<hex-encoded 32-byte AES key>
./bin/fuse                       # listens on :8080 (ORCH_LISTEN)

# Or run with no host configured — an in-memory stub is used, handy for local dev
./bin/fuse

Deploy

For anything past local dev, run the orchestrator as a service. The simplest topology co-locates it on a Firecracker host, and the host toolchain installs it next to the agent:

cd host-agent
./fc-install.sh                     # firecracker + kernel + rootfs
./fc-agent.sh install-service       # host agent (systemd, :8090)
./fc-agent.sh install-orchestrator  # orchestrator (systemd, :8080), co-located
sudoedit /etc/default/orchestrator  # set DATABASE_URL (Postgres)
sudo systemctl start orchestrator

install-orchestrator prefills /etc/default/orchestrator with this host's FIRECRACKER_TOKEN and generated auth/encryption keys (you supply only the Postgres DATABASE_URL), installs the unit, and prints the FUSE_BASE_URL + FUSE_TOKEN for the dashboard. Auth is required by default: the orchestrator refuses to boot until ORCH_AUTH_TOKEN and DATABASE_URL are set, and the Postgres schema is created on first start. Full walkthrough in host-agent/README.md.

Topology is just one env var. Leave FIRECRACKER_BASE_URL on loopback to co-locate, or point it at a remote agent (and register more hosts via /v1/hosts) to run the orchestrator as a standalone control plane scheduling across many hosts.

Dashboard

fuse-frontend is the Fuse Control Plane: a Phoenix/LiveView console for environments, hosts, snapshots, and a live event log, driving this orchestrator over its REST API. Point it at your orchestrator with the two values install-orchestrator prints:

Variable	Value
FUSE_BASE_URL	orchestrator URL, e.g. http://<host>:8080 (or your TLS proxy)
FUSE_TOKEN	the orchestrator's ORCH_AUTH_TOKEN (same value)

cd ../fuse-frontend
FUSE_BASE_URL=http://<host>:8080 FUSE_TOKEN=<orch-auth-token> mix phx.server
# dashboard on http://localhost:4000

The in-guest agent

Fuse doesn't hardcode a daemon. Boot drives a pluggable AgentSpec — files to upload, an optional download URL for the agent binary, and the commands to launch and gracefully drain it:

type AgentSpec struct {
    Files        map[string][]byte // arbitrary files uploaded into the guest
    DownloadURL  string            // optional: fetch the agent binary (e.g. a GitHub release)
    Command      string            // how to launch the daemon
    DrainCommand string            // graceful-stop command, run via Exec on drain
    AuthToken    string
    Gateway      string
    GatewayToken string
}

fused ships as the reference profile (FusedAgentSpec in agent_profile.go). To run your own agent, supply a different AgentSpec and bake your binary into the rootfs — see host-agent/FUSE.md.

Configuration

Env var	Flag	Default	Purpose
ORCH_LISTEN	--listen	:8080	API listen address
FIRECRACKER_BASE_URL	--firecracker-url	(empty → stub)	Firecracker host agent URL
FIRECRACKER_TOKEN			Bearer token for the host agent
DATABASE_URL	--database-url	(empty → in-memory)	Postgres state store
TOKEN_ENCRYPTION_KEY			Hex-encoded 32-byte AES key for per-VM token encryption
AGENT_DOWNLOAD_URL			URL to fetch the guest agent binary at boot
ORCH_TLS_CERT / ORCH_TLS_KEY			Serve the API over TLS
ORCH_REQUIRE_AUTH			Fail closed: refuse to boot unless ORCH_AUTH_TOKEN + DATABASE_URL are set
ORCH_AUTH_TOKEN / ORCH_ALLOWED_CIDRS			API auth + IP allowlist

API

REST on chi. The full surface is in the concept tables above; /metrics exposes Prometheus metrics (unauthenticated). Spec: internal/api/openapi.yaml.

Use cases

Coming soon. This section will collect real-world examples of how people run Fuse — from agent sandboxes to ephemeral CI runners and beyond. Using Fuse for something interesting? Open a PR and add it here.

Layout

cmd/orchestrator/        orchestrator server entrypoint (main)
cmd/fused/               reference in-guest agent (main)
cmd/dbcheck/             database-check utility (main)
internal/orchestrator/   Boot, AgentSpec, FleetManager, scheduler, reconcile, snapshots, state store
internal/orchestrator/agent_profile.go   fused reference profile (the only fused-aware Go file)
internal/api/            REST handlers
internal/firecracker/    Firecracker provider (talks to fc-agent)
internal/secrets/        per-VM credential generation + token encryption
internal/apikeys/        revocable API key store
internal/metrics/        Prometheus metrics
cli/                     operator CLI
sdks/                    client SDKs (go, python, typescript)
host-agent/              fc-agent host toolchain (bring up a Firecracker host)