# AdGuard DNS Mesh

Network-wide ad blocking and split-horizon DNS for all Headscale mesh nodes.

## Architecture

```
                    Headscale (Calypso)
                    pushes DNS config to all nodes
                           │
                    ┌──────┴──────┐
                    ▼              ▼
          Calypso AdGuard    Atlantis AdGuard
          100.103.48.78:53   100.83.230.112:53
          (primary)          (backup)
                    │              │
                    └──────┬──────┘
                           ▼
                  All Tailscale nodes
                  (ad blocking + split-horizon)
```

## How It Works

1. **Headscale** pushes two DNS nameservers (Tailscale IPs) to all connected nodes
2. Each node resolves DNS through **Calypso AdGuard** (primary) or **Atlantis AdGuard** (fallback)
3. AdGuard provides **ad blocking** (filter lists) and **split-horizon DNS** (38 rewrites for internal services)
4. Upstream DNS uses DoH: AdGuard DNS, Cloudflare, Quad9, Google, LibreDNS

## Headscale DNS Config

File: `/volume1/docker/headscale/config/config.yaml` on Calypso
Repo: `hosts/synology/calypso/headscale-config.yaml`

```yaml
dns:
  magic_dns: true
  base_domain: tail.vish.gg
  nameservers:
    global:
      - 100.103.48.78    # Calypso AdGuard (Tailscale IP)
      - 100.83.230.112   # Atlantis AdGuard (Tailscale IP)
```

Using Tailscale IPs (not LAN IPs) ensures remote nodes (Seattle, Jellyfish, mobile devices, GL.iNet routers) can reach the DNS servers.

## Split-Horizon DNS Rewrites (38 rules)

Both Calypso and Atlantis AdGuard instances have identical rewrites:

| Domain | Answer | Purpose |
|--------|--------|---------|
| `*.vish.gg` | `100.85.21.51` | Wildcard → matrix-ubuntu (NPM) |
| `pt.vish.gg` | `192.168.0.154` | Portainer (direct, not proxied) |
| `sso.vish.gg` | `192.168.0.154` | Authentik SSO |
| `git.vish.gg` | `192.168.0.154` | Gitea |
| `dash.vish.gg` | `192.168.0.154` | Homarr dashboard |
| `gf.vish.gg` | `192.168.0.154` | Grafana |
| `headscale.vish.gg` | `192.168.0.250` | Headscale server |
| `derp.vish.gg` | `192.168.0.250` | DERP relay (Calypso) |
| `derp-atl.vish.gg` | `192.168.0.200` | DERP relay (Atlantis) |
| `derp-sea.vish.gg` | `100.82.197.124` | DERP relay (Seattle) |
| `turn.thevish.io` | `192.168.0.200` | TURN server |
| `*.tail.vish.gg` | per-node Tailscale IP | MagicDNS node records (12) |
| `*.vish.local` | per-node Tailscale IP | Local aliases (8) |
| `*.crista.home` | per-node Tailscale IP | Crista network aliases (2) |
| `*.thevish.io` | `100.85.21.51` | thevish.io wildcard |
| `*.crista.love` | `100.85.21.51` | crista.love wildcard |

## Node Status

| Node | accept-dns | Split-Horizon | Ad Blocking | Notes |
|------|:---:|:---:|:---:|-------|
| homelab-vm | enabled | Yes | Yes | |
| atlantis | enabled | Yes | Yes | |
| seattle | enabled | Yes | Yes | Remote VPS |
| nuc | enabled | Yes | Yes | |
| pi-5 | enabled | Yes | Yes | |
| matrix-ubuntu | enabled | Yes | Yes | |
| jellyfish | enabled | Yes | Yes | No dig/nslookup, verified via python |
| calypso | enabled | N/A | N/A | IS the AdGuard server; Synology can't override resolv.conf |
| setillo | enabled | No | Yes (local) | Synology limitation; has own local AdGuard |
| guava | N/A | N/A | Via LAN | TrueNAS app; uses Calypso AdGuard at 192.168.0.250 on LAN |

Mobile devices, GL.iNet routers, and Home Assistant use default `--accept-dns=true` and inherit DNS from Headscale automatically.

## Rollback

### Immediate (~2 min) - revert Headscale DNS to LAN IPs

```bash
ssh calypso 'sed -i "s/100.103.48.78/192.168.0.250/" /volume1/docker/headscale/config/config.yaml && \
             sed -i "s/100.83.230.112/192.168.68.100/" /volume1/docker/headscale/config/config.yaml'
# Restart headscale via Portainer or:
ssh calypso '/usr/local/bin/docker restart headscale'
```

### Per-node override

```bash
# On the affected node:
tailscale set --accept-dns=false
```

### Nuclear - bypass Tailscale DNS entirely

```bash
echo "nameserver 1.1.1.1" | sudo tee /etc/resolv.conf
```

### Symptoms

| Symptom | Cause | Fix |
|---------|-------|-----|
| DNS resolution hangs | Both AdGuard containers down | Restart AdGuard on Calypso/Atlantis |
| Wrong split-horizon (public IP) | Rewrite missing on responding AdGuard | Add missing rewrite via AdGuard UI |
| One node can't resolve | Tailscale tunnel down | `tailscale ping calypso` to diagnose |

## AdGuard Instances

| Instance | Host | LAN IP | Tailscale IP | Web UI | Role |
|----------|------|--------|-------------|--------|------|
| Calypso | Synology | 192.168.0.250:9080 | 100.103.48.78:9080 | http://192.168.0.250:9080 | Primary |
| Atlantis | Synology | 192.168.0.200:9080 | 100.83.230.112:9080 | http://192.168.0.200:9080 | Backup |
| NUC | Intel NUC | 192.168.68.100:9080 | 100.72.55.21:9080 | http://192.168.68.100:9080 | Local (Concord subnet) |
| Setillo | Synology | 192.168.69.x | 100.125.0.20 | host network | Local (remote site) |

## Maintenance

When adding a new split-horizon rewrite, add it to **both** Calypso and Atlantis AdGuard instances to keep them in sync. Use the AdGuard web UI or API:

```bash
# Calypso (via MCP tool or API)
curl -u vish:PASSWORD -X POST http://192.168.0.250:9080/control/rewrite/add \
  -H 'Content-Type: application/json' \
  -d '{"domain":"new.vish.gg","answer":"192.168.0.154"}'

# Atlantis (same, different host)
curl -u vish:PASSWORD -X POST http://192.168.0.200:9080/control/rewrite/add \
  -H 'Content-Type: application/json' \
  -d '{"domain":"new.vish.gg","answer":"192.168.0.154"}'
```

---

*Deployed: 2026-03-31*
*Config: `hosts/synology/calypso/headscale-config.yaml`*
