240 lines
9.6 KiB
Markdown
240 lines
9.6 KiB
Markdown
# Split-Horizon DNS Implementation Guide
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Last updated: 2026-03-20
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## Problem
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All DNS queries for `*.vish.gg`, `*.thevish.io`, and `*.crista.love` currently resolve to Cloudflare proxy IPs (104.21.x.x), even when the client is on the same LAN as the services. This means:
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1. **Hairpin NAT** — LAN traffic goes out to Cloudflare and back in through the router
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2. **Internet dependency** — if the WAN link goes down, LAN services are unreachable by domain
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3. **Added latency** — ~50ms roundtrip through Cloudflare vs ~1ms on LAN
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4. **Cloudflare bottleneck** — all traffic proxied through CF even when unnecessary
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## Solution
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**Status: IMPLEMENTED (2026-03-20)**
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Use AdGuard Home on Calypso (primary) and Atlantis (backup) as **split-horizon DNS resolvers** that return local IPs for homelab domains when queried from the LAN, while external clients continue to use Cloudflare.
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```
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┌──────────────────────────────────┐
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│ DNS Query for │
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│ nb.vish.gg │
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└───────────────┬──────────────────┘
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│
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┌───────────────▼──────────────────┐
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│ Where is the client? │
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└───────┬───────────────┬──────────┘
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│ │
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LAN Client External Client
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│ │
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▼ ▼
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┌──────────────┐ ┌──────────────┐
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│ AdGuard Home │ │ Cloudflare │
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│ (Calypso + │ │ DNS │
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│ Atlantis) │ │ │
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│ Returns: │ │ Returns: │
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│100.85.21.51 │ │ 104.21.73.214│
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│(NPM Tailscale)│ │ (CF proxy) │
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└──────┬───────┘ └──────┬───────┘
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│ │
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▼ ▼
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┌──────────────┐ ┌──────────────┐
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│ NPM (local) │ │ Cloudflare │
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│ matrix-ubuntu│ │ → WAN IP │
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│ :443 ~1ms │ │ → NPM │
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└──────┬───────┘ │ ~50ms │
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│ └──────┬───────┘
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▼ ▼
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┌─────────────────────────────────┐
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│ Backend Service │
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│ (same result, faster path) │
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└─────────────────────────────────┘
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```
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## Prerequisites
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NPM is now on matrix-ubuntu (192.168.0.154) listening on standard ports 80/443/81. The migration from Calypso was completed on 2026-03-20.
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| Port | Status |
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|------|--------|
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| 80:80 | **Active** |
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| 443:443 | **Active** |
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| 81:81 | **Active** (Admin UI) |
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## Implementation Steps
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### Step 1: Move NPM to Standard Ports -- DONE
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NPM migrated from Calypso to matrix-ubuntu (192.168.0.154) on 2026-03-20. Compose file: `hosts/vms/matrix-ubuntu/nginx-proxy-manager.yaml`. Host nginx on matrix-ubuntu has been disabled (`systemctl disable nginx`); NPM now handles mastodon.vish.gg, mx.vish.gg, and mm.crista.love directly.
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Router port forwards updated:
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- `WAN:443 → 192.168.0.154:443`
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- `WAN:80 → 192.168.0.154:80`
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### Step 2: Configure AdGuard DNS Rewrites -- DONE
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AdGuard DNS rewrites configured on both Calypso (http://192.168.0.250:9080) and Atlantis (http://192.168.0.200:9080). Wildcard entries point to NPM's Tailscale IP:
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| Domain | Answer | Notes |
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|--------|--------|-------|
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| `*.vish.gg` | `100.85.21.51` | All vish.gg domains → NPM Tailscale IP |
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| `*.thevish.io` | `100.85.21.51` | All thevish.io domains → NPM Tailscale IP |
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| `*.crista.love` | `100.85.21.51` | All crista.love domains → NPM Tailscale IP |
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These three wildcards cover all 36 proxy hosts. AdGuard resolves matching queries locally instead of forwarding to upstream DNS.
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**Exceptions** — these domains need direct IPs (not NPM), added as specific overrides:
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| Domain | Answer | Reason |
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|--------|--------|--------|
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| `mx.vish.gg` | `192.168.0.154` | Matrix federation needs direct access on port 8448 |
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| `derp.vish.gg` | `192.168.0.250` | DERP relay — direct IP, no CF proxy |
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| `derp-atl.vish.gg` | `192.168.0.200` | Atlantis DERP relay |
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| `headscale.vish.gg` | `192.168.0.250` | Headscale control — direct access |
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| `turn.thevish.io` | `192.168.0.200` | TURN/STUN needs direct UDP |
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**.tail.vish.gg overrides** — specific rewrites to override the wildcard for Tailscale-specific subdomains.
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Specific entries take priority over wildcards in AdGuard.
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### Step 3: Set AdGuard as LAN DNS Server -- DONE
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Router (Archer BE800) DHCP configured with dual AdGuard DNS:
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1. **Primary DNS:** `192.168.0.250` (Calypso AdGuard)
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2. **Secondary DNS:** `192.168.0.200` (Atlantis AdGuard, backup)
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### Step 4: Configure Atlantis AdGuard (Backup DNS) -- DONE
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Same DNS rewrites added to Atlantis's AdGuard instance (http://192.168.0.200:9080) as backup:
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- Same wildcard rewrites as Calypso (pointing to `100.85.21.51`)
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- Reachable at `192.168.0.200`
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### Step 5: Test
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```bash
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# Verify local resolution
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dig nb.vish.gg @192.168.0.250
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# Expected: 192.168.0.250 (NPM local IP)
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# Verify external resolution still works
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dig nb.vish.gg @1.1.1.1
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# Expected: 104.21.73.214 (Cloudflare proxy)
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# Test HTTPS access via local DNS
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curl -s --resolve "nb.vish.gg:443:192.168.0.250" https://nb.vish.gg/ -o /dev/null -w "%{http_code} %{time_total}s\n"
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# Expected: 200 in ~0.05s (vs ~0.15s through Cloudflare)
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# Test all domains resolve locally
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for domain in nb.vish.gg gf.vish.gg git.vish.gg sso.vish.gg dash.vish.gg; do
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ip=$(dig +short $domain @192.168.0.250 | tail -1)
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echo "$domain → $ip"
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done
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```
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## SSL Considerations
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**Resolved:** NPM now uses **Let's Encrypt wildcard certificates** (DNS challenge via Cloudflare API) instead of Cloudflare Origin certs. This means:
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- Certs are trusted by all browsers, whether traffic comes through Cloudflare or directly via LAN
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- No browser warnings for split-horizon DNS LAN access
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- Certs auto-renew via NPM's built-in Let's Encrypt integration
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## What Changes for Each Path
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### LAN Client
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```
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Browser → nb.vish.gg
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→ AdGuard DNS: 100.85.21.51 (NPM Tailscale IP)
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→ NPM (matrix-ubuntu:443) → SSL termination (LE wildcard cert)
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→ Proxy to backend (192.168.0.210:8443)
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→ Response (~1ms total DNS+proxy)
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```
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### External Client
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```
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Browser → nb.vish.gg
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→ Cloudflare DNS: 104.21.73.214
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→ Cloudflare proxy → WAN IP → Router
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→ NPM (matrix-ubuntu:443) → SSL termination
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→ Proxy to backend (192.168.0.210:8443)
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→ Response (~50ms total)
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```
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### Internet Down
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```
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Browser → nb.vish.gg
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→ AdGuard DNS: 100.85.21.51 (cached/local)
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→ NPM (matrix-ubuntu:443) → SSL termination
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→ Proxy to backend
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→ Response (services still work!)
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```
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## Current NPM Proxy Hosts (for reference)
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All 36 domains that would benefit from split-horizon:
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### vish.gg (27 domains)
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| Domain | Backend |
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|--------|---------|
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| actual.vish.gg | calypso:8304 |
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| cal.vish.gg | atlantis:12852 |
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| dash.vish.gg | atlantis:7575 |
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| dav.vish.gg | calypso:8612 |
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| docs.vish.gg | calypso:8777 |
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| gf.vish.gg | homelab-vm:3300 |
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| git.vish.gg | calypso:3052 |
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| headscale.vish.gg | calypso:8085 |
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| kuma.vish.gg | rpi5:3001 |
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| mastodon.vish.gg | matrix-ubuntu:3000 |
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| mx.vish.gg | matrix-ubuntu:8082 |
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| nb.vish.gg | homelab-vm:8443 |
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| npm.vish.gg | calypso:81 |
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| ntfy.vish.gg | homelab-vm:8081 |
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| ollama.vish.gg | atlantis:11434 |
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| ost.vish.gg | calypso:3000 |
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| paperless.vish.gg | calypso:8777 |
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| pt.vish.gg | atlantis:10000 |
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| pw.vish.gg | atlantis:4080 |
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| rackula.vish.gg | calypso:3891 |
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| retro.vish.gg | calypso:8025 |
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| rx.vish.gg | calypso:9751 |
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| rxdl.vish.gg | calypso:9753 |
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| scrutiny.vish.gg | homelab-vm:8090 |
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| sf.vish.gg | calypso:8611 |
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| sso.vish.gg | calypso:9000 |
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| wizarr.vish.gg | atlantis:5690 |
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### thevish.io (5 domains)
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| Domain | Backend |
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|--------|---------|
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| binterest.thevish.io | homelab-vm:21544 |
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| hoarder.thevish.io | homelab-vm:3482 |
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| joplin.thevish.io | atlantis:22300 |
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| matrix.thevish.io | matrix-ubuntu:8081 |
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| meet.thevish.io | atlantis:5443 |
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### crista.love (2 domains)
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| Domain | Backend |
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|--------|---------|
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| crista.love | guava:28888 |
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| cocalc.crista.love | guava:8080 |
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| mm.crista.love | matrix-ubuntu:8065 |
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## Rollback
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If something breaks:
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1. Change router DHCP DNS back to `1.1.1.1` / `8.8.8.8`
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2. Or remove the DNS rewrites from AdGuard
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3. All traffic reverts to Cloudflare path immediately
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## Related Documentation
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- [NPM Migration](npm-migration-jan2026.md) — Reverse proxy configuration
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- [Authentik SSO](authentik-sso.md) — Forward auth depends on NPM routing
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- [Cloudflare DNS](cloudflare-dns.md) — External DNS records
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- [Image Update Guide](../admin/IMAGE_UPDATE_GUIDE.md) — Mentions Gitea/NPM as bootstrap dependencies
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