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GMC Server (Gateway Management Controller)

Manual Service - Not Managed by Domain Manager

GMC uses UDP port forwarding via Docker relay, NOT Traefik. The domain entry in Domain Manager has service_type: manual to prevent accidental misconfiguration.

Overview

Property Value
Domain gmc.microshare.eu
Public IP 51.68.235.106 (hub2)
Protocol UDP
Port 39015
Backend VM 2912 (gmc-server) via WireGuard
Backend IP REDACTED_IP
Service Type manual (externally managed)

Architecture

XE300 Gateway (Internet)
        │
        ▼ UDP 39015
hub2 public IP (51.68.235.106)
        │
        ▼ Binds directly (host networking)
gmc-relay container (socat)
        │
        ▼ UDP forward to REDACTED_IP:39015
WireGuard VPN (wg-uk interface)
        │
        ▼
GMC Server (REDACTED_IP:39015)
    VM 2912 on px1-silverstone

Why This Architecture

  1. UDP, not HTTP/HTTPS - Traefik handles HTTP traffic; UDP requires special handling
  2. No SSL termination - Raw UDP packets forwarded directly
  3. WireGuard VPN - GMC server is reachable via WireGuard for stable connectivity
  4. Docker-managed - Declarative config in docker-compose.yml, auto-restart
  5. IoT devices - XE300 gateways have hardcoded server address

Configuration

Docker Service

The relay is defined in /opt/charliehub/docker-compose.yml:

gmc-relay:
  image: alpine/socat:latest
  container_name: charliehub_gmc_relay
  restart: unless-stopped
  network_mode: host
  command: UDP-LISTEN:39015,fork,reuseaddr UDP:${GMC_IP}:${GMC_PORT}
  labels:
    - "traefik.enable=false"

Environment Variables

In /opt/charliehub/.env:

# GMC Server via WireGuard (VM 2912 on px1)
GMC_IP=REDACTED_IP
GMC_PORT=39015

UFW Rule

UDP 39015 is allowed through UFW:

sudo ufw status | grep 39015
# 39015/udp   ALLOW   Anywhere   # GMC WireGuard for XE300 gateways

GMC Server (VM 2912)

The GMC server runs on VM 2912 (px1-silverstone, UK homelab):

Property Value
VM ID 2912
Hostname gmc-server
Proxmox Host px1-silverstone
LAN IP REDACTED_IP

Verification

Check relay is running

docker ps | grep gmc-relay
docker logs charliehub_gmc_relay

Check port is listening

sudo ss -ulnp | grep 39015
# Should show socat listening on *:39015

Check WireGuard connectivity to GMC

# From hub2
ping REDACTED_IP

# Check WireGuard interface
sudo wg show wg-uk

Check XE300 connectivity

On the XE300 gateway:

wg show
# Should show:
#   latest handshake: X seconds ago
#   transfer: XX KiB received, XX KiB sent

Troubleshooting

XE300 not connecting (0 B received)

  1. Check relay is running: 

    docker ps | grep gmc-relay

  2. Check GMC server is reachable via WireGuard: 

    ping REDACTED_IP

  3. Check GMC service is listening: 

    # From hub2 or any WireGuard-connected device
nc -uvz REDACTED_IP 39015

  4. Check UFW allows UDP 39015: 

    sudo ufw status | grep 39015

Relay not starting

# Check logs
docker logs charliehub_gmc_relay

# Verify env vars are set
grep GMC /opt/charliehub/.env

# Restart
cd /opt/charliehub && docker compose restart gmc-relay

Operations

Restart the relay

cd /opt/charliehub && docker compose restart gmc-relay

Update GMC IP

If GMC server moves or gets a new IP:

# 1. Update .env
nano /opt/charliehub/.env
# Change GMC_IP=REDACTED_IP to new IP

# 2. Restart relay
cd /opt/charliehub && docker compose restart gmc-relay

View traffic

# Watch relay logs
docker logs -f charliehub_gmc_relay

# Watch packet counts on hub2
sudo tcpdump -i any udp port 39015 -c 10

Dependencies

Component Required For
WireGuard (wg-uk) Route to UK homelab (10.44.x.x)
UFW rule Allow UDP 39015 through firewall
Docker Run gmc-relay container
socat UDP forwarding