Wrenn

Secure infrastructure for AI

Prerequisites

• Linux host with /dev/kvm access (bare metal or nested virt)
• Firecracker binary at /usr/local/bin/firecracker
• PostgreSQL
• Go 1.25+
• pnpm (for frontend)
• Docker (for dev infra and rootfs builds)

Build

make build    # outputs to builds/

Produces three binaries: wrenn-cp (control plane), wrenn-agent (host agent), envd (guest agent).

Host setup

The host agent needs a kernel, a minimal rootfs image, and working directories on the host machine.

Directory structure

/var/lib/wrenn/
├── kernels/
│   └── vmlinux              # uncompressed Linux kernel (not bzImage)
├── images/
│   └── minimal/
│       └── rootfs.ext4      # base rootfs (all other templates snapshot from this)
├── sandboxes/               # per-sandbox CoW files (created at runtime)
└── snapshots/               # pause/hibernate snapshot files (created at runtime)

Create the directories:

sudo mkdir -p /var/lib/wrenn/{kernels,images/minimal,sandboxes,snapshots}

Kernel

Place an uncompressed vmlinux kernel at /var/lib/wrenn/kernels/vmlinux. Versioned kernels (vmlinux-{semver}) are also supported — the agent picks the latest by semver.

Minimal rootfs

The minimal rootfs is the base image that all other templates (Python, Node, etc.) are built on top of via device-mapper snapshots. It must contain:

Package	Why
socat	Bidirectional relay for port forwarding
chrony	Time sync from KVM PTP clock (/dev/ptp0)
tini	PID 1 zombie reaper (injected by build script, not apt)
sudo	User privilege management inside the guest
wget	HTTP fetching
curl	HTTP client
ca-certificates	TLS certificate verification

To build a rootfs from a Docker container:

1. Create and configure a container with the required packages:

   docker run -it --name wrenn-minimal debian:bookworm bash
   # Inside the container:
   apt update && apt install -y socat chrony sudo wget curl ca-certificates
   exit
   

2. Export to a rootfs image (builds envd, injects wrenn-init + tini, shrinks to minimum size):

   sudo bash scripts/rootfs-from-container.sh wrenn-minimal minimal
   

To update an existing rootfs after changing envd or wrenn-init.sh:

bash scripts/update-minimal-rootfs.sh

This rebuilds envd via make build-envd and copies the fresh binaries into the mounted rootfs image.

IP forwarding

sudo sysctl -w net.ipv4.ip_forward=1

Configure

Copy .env.example to .env and edit:

# Required
DATABASE_URL=postgres://wrenn:wrenn@localhost:5432/wrenn?sslmode=disable

# Control plane
WRENN_CP_LISTEN_ADDR=:8000
CP_HOST_AGENT_ADDR=http://localhost:50051

# Host agent
WRENN_HOST_LISTEN_ADDR=:50051
WRENN_DIR=/var/lib/wrenn

Development

make dev          # Start PostgreSQL (Docker), run migrations, start control plane
make dev-agent    # Start host agent (separate terminal, sudo)
make dev-frontend # Vite dev server with HMR (port 5173)
make check        # fmt + vet + lint + test

Host registration

Hosts must be registered with the control plane before they can serve sandboxes.

1. Create a host record (via API or dashboard):

   curl -X POST http://localhost:8000/v1/hosts \
     -H "Authorization: Bearer $JWT_TOKEN" \
     -H "Content-Type: application/json" \
     -d '{"type": "regular"}'
   

   This returns a registration_token (valid for 1 hour).

2. Start the host agent with the registration token and its externally-reachable address:

   sudo WRENN_CP_URL=http://localhost:8000 \
        ./builds/wrenn-agent \
        --register <token-from-step-1> \
        --address <host-ip>:50051
   

   On first startup the agent sends its specs (arch, CPU, memory, disk) to the control plane, receives a long-lived host JWT, and saves it to $WRENN_DIR/host-token.

3. Subsequent startups don't need --register — the agent loads the saved JWT automatically:

   sudo ./builds/wrenn-agent --address <host-ip>:50051
   

4. If registration fails (e.g., network error after token was consumed), regenerate a token:

   curl -X POST http://localhost:8000/v1/hosts/$HOST_ID/token \
     -H "Authorization: Bearer $JWT_TOKEN"
   

   Then restart the agent with the new token.

The agent sends heartbeats to the control plane every 30 seconds.

See CLAUDE.md for full architecture documentation.