public/docs/dns-naming.md

🌐 DNS Naming Model

Note

DNS isn't just naming in this fleet — it's the mechanism that decides which trust boundary a request enters. Which zone a hostname resolves in determines whether a request gets mutual-TLS-and-SSO treatment, a lighter-weight trusted-IP path, or the public internet-facing edge entirely. Get the DNS answer wrong and you've effectively picked the wrong security posture for that request.

Server	Technitium DNS Server — self-hosted, open-source, chosen over a managed/cloud DNS provider specifically so internal zone data never leaves the LAN
Zones	Two internal zones, deliberately never merged, plus one public exception
Enforcement	Every host's resolver is pointed at this server only — direct outbound DNS to anywhere else is blocked at the firewall
Depends on	Nothing upstream for internal resolution — it's the root of trust for internal naming
Depended on by	Every system in this repo that resolves a hostname — which is effectively all of them

Why self-hosted DNS at all

A homelab this size could get away with a shared hosts file or a single flat zone. Two things specifically ruled that out:

1. The two-zone trust model needs a real answer to "which front door am I behind." Splitting traffic into a mutual-TLS-enforced browser zone and a lighter trusted-IP internal zone (see docs/firewall-and-network.md) only works if something authoritative decides, per-hostname, which zone a request lands in. A hosts file can't do that at scale across a dozen-plus hosts; a real DNS server with two real zones can.
2. Every other system needs one source of truth for internal names. The secrets platform issues a certificate to the DNS server's own admin interface (see below); the orchestration engine resolves every fleet host by name before it can SSH anywhere; the observability pipeline ships DNS query logs as their own dedicated stream. Hand-rolling internal name resolution per-app would mean N inconsistent answers instead of one.

The two zones

flowchart TD
    Client["Anything on the LAN"] --> DNS["Technitium DNS"]
    DNS --> ZoneA["Zone A: browser-facing"]
    DNS --> ZoneB["Zone B: app-to-app"]
    DNS -.unresolved.-> Forward["Forwards to the edge firewall<br/>+ a couple of public resolvers"]

    ZoneA --> EdgeProxy["User-facing reverse proxy<br/>mTLS + SSO enforced"]
    ZoneB --> InternalProxy["Internal reverse proxy<br/>trusted-IP allowlist, no mTLS"]

Zone	Resolves to	Enforcement	Used by
Browser-facing	The user-facing reverse proxy	Mutual TLS (client cert required) + SSO	Anything a human opens in a browser
App-to-app	The internal reverse proxy	Trusted-IP allowlist bypass, or SSO forward-auth for anything not on that allowlist	Webhooks, API integrations, service-to-service calls

Most apps that need both human and machine access get one hostname per zone — same app, two different front doors, chosen by which zone the caller resolves it in. Not every app needs both: a purely internal API integration might only ever get the app-to-app hostname; an app nobody automates against might only get the browser-facing one. The two zones aren't kept in lockstep by policy — a periodic audit is what actually catches when they drift, not an assumption that they match.

Tip

The public exception, and why it's a real exception and not a bug: a self-hosted blog in this fleet is genuinely meant to be reached from the open internet, routed through the edge firewall's own public reverse-proxy layer (see docs/firewall-and-network.md). It has zero presence in either internal zone — not because it was forgotten, but because a third DNS entry pointing at an app that already has its own public-facing edge route would just be redundant. Apps meant for the public internet skip the internal model entirely rather than being forced into it.

DNS as an enforced boundary, not just a convenience

Important

Every host on the LAN has its resolver pointed at this one internal DNS server — and that's enforced, not just configured. Direct outbound DNS queries to anywhere else (a public resolver, another host acting as its own resolver) are blocked at the firewall level, covered in docs/firewall-and-network.md. This closes a real bypass: without it, any host could sidestep the internal zones entirely by just asking a public resolver instead, which would quietly undermine the whole two-zone trust model above. DNS enforcement is what makes the rest of this architecture actually load-bearing instead of advisory.

Where DNS shows up in every other system

DNS isn't a standalone concern in this fleet — it's a dependency almost everything else sits on top of:

System	How it depends on DNS
Secrets & PKI	The secrets platform issues the DNS server's own admin-UI certificate; separately, every Vault Agent across the fleet has to resolve its target before it can even open a connection
SSO & Identity	The OIDC redirect dance depends on the identity provider's hostname resolving correctly on the internal zone, even when the app being logged into lives on the browser-facing one
Firewall & Network Segmentation	DNS-bypass prevention (above) is enforced as an explicit firewall rule, not a DNS-server-side restriction
Observability	DNS query logs are their own dedicated ingestion pipeline into the log aggregator, kept separate from general system/container logs
Orchestration	Every scheduled maintenance flow resolves its target hosts by name before it can reach them over SSH
Architecture Overview	DNS resolution is explicitly the mechanism that determines which of the fleet's routing/trust planes a given request enters

---

Related stacks: stacks/platform/caddy/, stacks/platform/caddy-internal/