# ADR-0035: The public TLS edge is a Caddy deployment in the cluster

- **Status:** Accepted
- **Date:** 2026-09-18
- **Deciders:** Respellion engineering
- **Slice:** [#177](https://git.labs.respellion.tech/eho/register-referentie/issues/177)

## Context

The stack deploys to a Talos VM on the lab server (ADR-0033, issue #175). Until now it was
only usable through five SSH port-forwards: the portals' OIDC flow uses PKCE, PKCE needs
`crypto.subtle`, and browsers expose that only in a **secure context** — HTTPS or an origin
on `localhost`. A NodePort on the VM's address is neither, so the deployment was pinned to
`host: localhost` and every viewer had to forward all five browser-facing ports (a portal
without Keycloak on the same `localhost:30180` fails on the discovery document).

That is not a demo anyone can be sent a link to. We want public hostnames with real
certificates — and we want the routing and the certificates to be cluster state, not
host-side configuration that no `helm upgrade` can see.

The public IP is on the Fedora host (`46.224.220.37`); the cluster is a libvirt guest
behind it.

## Decision

**Terminate TLS in the cluster, with a Caddy deployment rendered by the chart
(`templates/edge.yaml`), and give the Fedora host nothing but a layer-4 forward.**

- `public.domain` is the single switch. Empty — the default, and what compose and CI use —
  renders nothing: the stack is reached on its NodePorts and `host` pins the OIDC origin
  exactly as before. Set it, and the edge appears.
- `public.routes` maps a subdomain to an in-cluster `service:port`. Caddy proxies to the
  **ClusterIP** services, so a public deployment does not use the browser-facing NodePorts
  at all.
- Caddy obtains and renews certificates itself (ACME HTTP-01). There is no cert-manager.
- The host forwards `:80`/`:443` to two NodePorts with two `firewall-cmd
  --add-forward-port` rules. No TLS, no routing, no per-service knowledge there — adding a
  portal is a chart change, not a host change.
- `KC_HOSTNAME` and the portals' `config.json` stop being `host` + NodePort. Both now come
  from one helper, `big.keycloakUrl`, so the issuer Keycloak pins and the authority the
  portals are configured with cannot drift apart (ADR-0010).

### Alternatives considered

- **Caddy on the Fedora host.** Fewest moving parts — but the routing table and the
  certificates would live outside the cluster, in a file no deployment touches, and adding
  a portal would mean editing a host we deploy to over SSH. Rejected on exactly the ground
  this ADR exists to record.
- **Traefik or ingress-nginx, plus cert-manager.** The conventional answer, and the right
  one for a cluster with many teams and changing hostnames. Here it buys a controller, a
  set of CRDs and Ingress objects to describe five hostnames that never change — and
  cert-manager to do what Caddy already does unprompted.
- **A `LoadBalancer` service (MetalLB).** Solves address allocation, which is not the
  problem; the node has exactly one address and it still is not the public one.
- **Keep the SSH forwards.** Free, and genuinely fine for one developer. It is not a demo
  you can send to someone.

## Consequences

**Positive**

- No new dependency: the four portals already run `caddy:2-alpine` (ADR-0034), whose
  ceiling note called this out — *"a real hostname makes TLS a one-line `Caddyfile`
  change"*. This is that change.
- Routing is cluster state: `kubectl -n big get cm caddy-edge-config -o yaml` is the whole
  truth about what is published, and `helm upgrade` is how it changes.
- The secure context is real, so `TALOS_HOST=localhost` and the five forwards disappear —
  and with them the class of failure where a mismatched issuer logs the user out silently.
- Nothing changes for compose, CI or a laptop cluster: with `public.domain` empty the
  rendered manifests are byte-identical to before.

**Negative / costs**

- The host forward is irreducible. Two firewalld rules, applied by hand once, with `sudo`
  on a machine our pipeline reaches only over SSH. If someone rebuilds that host, the stack
  is unreachable until they are re-applied, and nothing in the cluster can tell them so.
- **Certificates need a volume.** On the default `emptyDir` every pod restart asks Let's
  Encrypt again, and its duplicate-certificate limit is five per week — a handful of
  restarts and the edge serves an untrusted certificate for a week. `persistence.storageClass`
  stops being optional for anything public (runbook §6).
- **All five hostnames are published, including `behandel` and `beheer`**, which approve
  registrations and administer the register. They are protected by synthetic accounts with
  well-known passwords, and by MFA on the medewerker realm (ADR-0031). That is a deliberate
  choice for a demonstration environment holding synthetic data only, and it is the reason
  this bullet is in the ADR rather than in a comment: if this stack ever holds anything
  real, this decision is the first one to revisit.
- One more workload in the chart with no counterpart in compose — compose has no edge
  because it has no hostname. The drift check (`make k8s-drift`) renders the defaults, so
  it does not see it.
- `auth` is load-bearing: `big.keycloakUrl` builds the issuer from that subdomain, so
  renaming the key in `public.routes` without the helper breaks every login. Both carry a
  comment saying so.

- ponytail ceiling: one replica, no HSTS, no security headers beyond Caddy's defaults, no
  rate limiting, and HTTP-01 rather than DNS-01 (so a wildcard certificate is not
  available). Upgrade path in that order; DNS-01 first if the subdomain list ever grows.

## Coupling rules touched (CLAUDE.md §8)

None. §8.3 holds — the browser reaches a portal, the portal reverse-proxies its own BFF
group, and the edge is in front of all of it. The edge terminates TLS and routes by
hostname; it does not know what any service does.