disinto/tools/edge-control

Edge Control Plane

SSH-forced-command control plane for managing reverse tunnels to edge hosts.

Overview

This control plane runs on the public edge host (Debian DO box) and provides:

• Self-service tunnel registration: Projects run disinto edge register to get an assigned port and FQDN
• SSH forced commands: Uses restrict,command="..." authorized_keys entries — no new HTTP daemon
• Hot-patched Caddy routing: <project>.disinto.ai → 127.0.0.1:<port> via Caddy admin API
• Port allocator: Manages ports in 20000-29999 range with flock-based concurrency control

Architecture

┌─────────────────────────────────────────────────────────────────────────────┐
│                           Edge Host (Debian DO)                              │
│                                                                              │
│  ┌──────────────────┐    ┌───────────────────────────────────────────────┐  │
│  │  disinto-register│    │  /var/lib/disinto/                            │  │
│  │  (authorized_keys│    │  ├── registry.json (source of truth)          │  │
│  │   forced cmd)    │    │  ├── registry.lock (flock)                    │  │
│  │                  │    │  └── authorized_keys (rebuildable)            │  │
│  └────────┬─────────┘    └───────────────────────────────────────────────┘  │
│           │                                                                   │
│           ▼                                                                   │
│  ┌─────────────────────────────────────────────────────────────────────┐     │
│  │  register.sh (forced command handler)                                │     │
│  │  ──────────────────────────────────────────────────────────────────  │     │
│  │  • Parses SSH_ORIGINAL_COMMAND                                       │     │
│  │  • Dispatches to register|deregister|list                            │     │
│  │  • Returns JSON on stdout                                            │     │
│  └─────────────────────────────────────────────────────────────────────┘     │
│           │                                                                   │
│           │ lib/                                                              │
│           ├─ ports.sh    → port allocator (20000-29999)                      │
│           ├─ authorized_keys.sh → rebuild authorized_keys from registry     │
│           └─ caddy.sh    → Caddy admin API (127.0.0.1:2019)                  │
│                                                                              │
│  ┌─────────────────────────────────────────────────────────────────────┐     │
│  │  Caddy (with Gandi DNS plugin)                                       │     │
│  │  ──────────────────────────────────────────────────────────────────  │     │
│  │  • Admin API on 127.0.0.1:2019                                       │     │
│  │  • Wildcard *.disinto.ai cert (DNS-01 via Gandi)                     │     │
│  │  • Site blocks hot-patched via admin API                             │     │
│  └─────────────────────────────────────────────────────────────────────┘     │
│                                                                              │
│  ┌─────────────────────────────────────────────────────────────────────┐     │
│  │  disinto-tunnel (no shell, no password)                              │     │
│  │  ──────────────────────────────────────────────────────────────────  │     │
│  │  • Receives reverse tunnels only                                     │     │
│  │  • authorized_keys: permitlisten="127.0.0.1:<port>"                  │     │
│  └─────────────────────────────────────────────────────────────────────┘     │
└─────────────────────────────────────────────────────────────────────────────┘

Installation

Prerequisites

• Fresh Debian 12 (Bookworm) system
• Root or sudo access
• Domain disinto.ai hosted at Gandi with API token

One-Click Install

# Download and run installer
curl -sL https://raw.githubusercontent.com/disinto-admin/disinto/fix/issue-621/tools/edge-control/install.sh | bash -s -- --gandi-token YOUR_GANDI_API_TOKEN

# You'll be prompted to paste your admin pubkey for the disinto-register user

What install.sh Does

1. Creates users:

   • disinto-register — owns registry, runs Caddy admin API calls
   • disinto-tunnel — no password, no shell, only receives reverse tunnels

2. Creates data directory:

   • /var/lib/disinto/ with registry.json, registry.lock
   • Permissions: root:disinto-register 0750

3. Installs Caddy:

   • Download Caddy with Gandi DNS plugin
   • Enable admin API on 127.0.0.1:2019
   • Configure wildcard cert for *.disinto.ai via DNS-01

4. Sets up SSH:

   • Creates disinto-register authorized_keys with forced command
   • Creates disinto-tunnel authorized_keys (rebuildable from registry)

5. Installs control plane scripts:

   • /opt/disinto-edge/register.sh — forced command handler
   • /opt/disinto-edge/lib/*.sh — helper libraries

Usage

Register a Tunnel (from dev box)

# First-time setup (generates tunnel keypair)
disinto edge register myproject

# Subsequent runs are idempotent
disinto edge register myproject  # returns same port/FQDN

Response:

{"port":23456,"fqdn":"myproject.disinto.ai"}

These values are written to .env as:

EDGE_TUNNEL_HOST=edge.disinto.ai
EDGE_TUNNEL_PORT=23456
EDGE_TUNNEL_FQDN=myproject.disinto.ai

Deregister a Tunnel

disinto edge deregister myproject

This:

• Removes the authorized_keys entry for the tunnel
• Removes the Caddy site block
• Frees the port in the registry

Check Status

disinto edge status

Shows all registered tunnels with their ports and FQDNs.

Registry Schema

/var/lib/disinto/registry.json:

{
  "version": 1,
  "projects": {
    "myproject": {
      "port": 23456,
      "fqdn": "myproject.disinto.ai",
      "pubkey": "ssh-ed25519 AAAAC3Nza... operator@devbox",
      "registered_at": "2026-04-10T14:30:00Z"
    }
  }
}

Recovery

After State Loss

If registry.json is lost but Caddy config persists:

# Rebuild from existing Caddy config
ssh disinto-register@edge.disinto.ai '
  /opt/disinto-edge/lib/rebuild-registry-from-caddy.sh
'

Rebuilding authorized_keys

If authorized_keys is corrupted:

ssh disinto-register@edge.disinto.ai '
  /opt/disinto-edge/lib/rebuild-authorized-keys.sh
'

Rotating Admin Key

To rotate the disinto-register admin pubkey:

# On edge host, remove old pubkey from authorized_keys
# Add new pubkey: echo "new-pubkey" >> /home/disinto-register/.ssh/authorized_keys
# Trigger rebuild: /opt/disinto-edge/lib/rebuild-authorized-keys.sh

Adding a Second Edge Host

For high availability, add a second edge host:

1. Run install.sh on the second host
2. Configure Caddy to use the same registry (NFS or shared storage)
3. Update EDGE_HOST in .env to load-balance between hosts
4. Use a reverse proxy (HAProxy, Traefik) in front of both edge hosts

Security

What's Protected

• No new attack surface: sshd is already the only listener; control plane is a forced command
• Restricted tunnel user: disinto-tunnel cannot shell in, only receive reverse tunnels
• Port validation: Tunnel connections outside allocated ports are refused
• Forced command: disinto-register can only execute register.sh

Certificate Strategy

• Single wildcard *.disinto.ai cert via DNS-01 through Gandi
• Caddy handles automatic renewal
• No per-project cert work needed

Future Considerations

• Long-term "shop" vision could layer an HTTP API on top
• forward_auth / OAuth is out of scope (handled per-project inside edge container)

Testing

Verify Tunnel User Restrictions

# Should hang (no command given)
ssh -i tunnel_key disinto-tunnel@edge.disinto.ai

# Should fail (port outside allocation)
ssh -R 127.0.0.1:9999:localhost:80 disinto-tunnel@edge.disinto.ai

# Should succeed (port within allocation)
ssh -R 127.0.0.1:23456:localhost:80 disinto-tunnel@edge.disinto.ai

Verify Admin User Restrictions

# Should fail (not a valid command)
ssh disinto-register@edge.disinto.ai "random command"

# Should succeed (valid command)
ssh disinto-register@edge.disinto.ai "register myproject $(cat ~/.ssh/id_ed25519.pub)"

Files

• install.sh — One-shot installer for fresh Debian DO box
• register.sh — Forced-command handler (dispatches to register|deregister|list)
• lib/ports.sh — Port allocator over 20000-29999, jq-based, flockd
• lib/authorized_keys.sh — Deterministic rebuild of disinto-tunnel authorized_keys
• lib/caddy.sh — POST to Caddy admin API for route mapping

Dependencies

• bash — All scripts are bash
• jq — JSON parsing for registry
• flock — Concurrency control for registry updates
• caddy — Web server with admin API and Gandi DNS plugin
• ssh — OpenSSH for forced commands and reverse tunnels