Wrenn Sandbox

MicroVM-based code execution platform. Firecracker VMs, not containers. Pool-based pricing, persistent sandboxes, Python/TS/Go SDKs.

Deployment

Prerequisites

• Linux host with /dev/kvm access (bare metal or nested virt)
• Firecracker binary at /usr/local/bin/firecracker
• PostgreSQL
• Go 1.25+

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 machine needs:

# Kernel for guest VMs
mkdir -p /var/lib/wrenn/kernels
# Place a vmlinux kernel at /var/lib/wrenn/kernels/vmlinux

# Rootfs images
mkdir -p /var/lib/wrenn/images
# Build or place .ext4 rootfs images (e.g., minimal.ext4)

# Sandbox working directory
mkdir -p /var/lib/wrenn/sandboxes

# Enable IP forwarding
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
CP_LISTEN_ADDR=:8000
CP_HOST_AGENT_ADDR=http://localhost:50051

# Host agent
AGENT_LISTEN_ADDR=:50051
AGENT_KERNEL_PATH=/var/lib/wrenn/kernels/vmlinux
AGENT_IMAGES_PATH=/var/lib/wrenn/images
AGENT_SANDBOXES_PATH=/var/lib/wrenn/sandboxes

Run

# Apply database migrations
make migrate-up

# Start control plane
./builds/wrenn-cp

Control plane listens on CP_LISTEN_ADDR (default :8000).

Host registration

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

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

   # As an admin (JWT auth)
   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 AGENT_CP_URL=http://cp-host:8000 \
        ./builds/wrenn-agent \
        --register <token-from-step-1> \
        --address 10.0.1.5:50051
   

   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 AGENT_TOKEN_FILE (default /var/lib/wrenn/host-token).

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

   sudo AGENT_CP_URL=http://cp-host:8000 \
        ./builds/wrenn-agent --address 10.0.1.5:50051
   

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. Host agent listens on AGENT_LISTEN_ADDR (default :50051).

Rootfs images

envd must be baked into every rootfs image. After building:

make build-envd
bash scripts/update-debug-rootfs.sh /var/lib/wrenn/images/minimal.ext4

Development

make dev          # Start PostgreSQL (Docker), run migrations, start control plane
make dev-agent    # Start host agent (separate terminal, sudo)
make check        # fmt + vet + lint + test

See CLAUDE.md for full architecture documentation.