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notandClaude Opus 5.5 84cea6267e docs(arch): ADR-0035 — publish the stack through the existing labs Caddy (closes #177)
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Records the decision #177 asked for, the other way round: the hypervisor has no
inbound path and the labs Caddy already holds 80/443 and the wildcard cert, so
the portals go through it over a reverse SSH tunnel instead of an in-cluster
edge. Covers keycloakUrl, KC_PROXY_HEADERS and the optional demo OTP autofill.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
2026-09-25 15:05:38 +02:00
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# ADR-0035: The deployed stack is published through the existing labs Caddy
- **Status:** Accepted
- **Date:** 2026-09-25
- **Deciders:** Respellion engineering
- **Slice:** [#177](https://git.labs.respellion.tech/eho/register-referentie/issues/177) —
that issue proposed the opposite (an in-cluster Caddy edge); this ADR records why the
host-side option won. Implemented in #179, #180 and #181.
## Context
The stack deploys to a single-node Talos VM (ADR-0033, #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**, meaning HTTPS or a
`localhost` origin. A NodePort on the VM's address is neither. We want a URL a demo
audience can simply open.
Three facts about where things run shape the answer:
- The Talos VM is a libvirt guest on a **Fedora hypervisor in the office**, behind NAT
with no public address. The only way in from outside is an existing reverse SSH tunnel
(`autossh-reverse-tunnel.service`) into an `openssh-server` container on the labs
server.
- The **labs server** (public IP) already runs Caddy for `*.labs.respellion.tech`, with
the wildcard certificate (DNS-01 via Cloudflare) and ports 80/443. Every other labs
service is published there (repo `Infra`, `infra/development/`).
- #177 proposed a Caddy **inside the cluster**, fed by a layer-4 forward on the host, so
that routing and certificates would be cluster state. That assumes the public IP is on
the hypervisor. It isn't: the hypervisor has no inbound path, and 80/443 on the labs
server are already taken by the labs Caddy.
## Decision
**Publish the portals and Keycloak through the existing labs Caddy. Carry the traffic to
the cluster over a second reverse SSH tunnel from the hypervisor.**
```
browser ─https─▶ labs Caddy ─▶ openssh-server:3014x/30180
─reverse SSH tunnel─▶ Fedora hypervisor ─▶ Talos NodePorts
```
- **Hostnames** under the existing wildcard: `big-register` (openbaar), `big-mijn`
(self-service), `big-behandel`, `big-beheer`, and `big-auth` (Keycloak, with `/admin*`
answered 404).
- **Tunnel:** `big-portals-tunnel.service` on the hypervisor (repo `Infra`)
reverse-forwards the five browser-facing NodePorts into `openssh-server`. It is
separate from the access tunnel on `:6667`, so a failed forward can't cut SSH access.
Caddy joins the `openssh_default` network to reach the tunnel ends.
- **Keycloak's issuer** is the public origin. The chart value `keycloakUrl` replaces
`host` + NodePort in one helper, `big.keycloakUrl`, which feeds both `KC_HOSTNAME` and
the portals' `config.json` authority, so the two cannot drift (ADR-0010). The deploy
workflow sets it from the `KEYCLOAK_URL` repository variable.
- **`KC_PROXY_HEADERS=xforwarded`:** `KC_HOSTNAME_BACKCHANNEL_DYNAMIC` builds the token,
userinfo and certs URLs from the request. That request reaches Keycloak as plain HTTP,
so the URLs came out `http://` and browsers blocked them as mixed content. Trusting
Caddy's `X-Forwarded-Proto` keeps them HTTPS. In-cluster calls send no such header and
still use `keycloak:8080`.
- **Demo MFA (optional):** `demo.otpAutofill` (`OTP_AUTOFILL`) makes the `big-demo` theme
(`infra/keycloak/themes/big-demo`) Keycloak's default. Its script fills in and submits
the medewerker OTP from the fixture secret (ADR-0031), so the step is visibly enforced
without an authenticator. It is off by default.
### Alternatives considered
- **In-cluster Caddy edge (#177, PR #178).** It would keep routes and certificates in
cluster state. But it needs a public inbound path to the hypervisor that doesn't exist,
plus a second certificate authority beside the labs Caddy, which already holds the
wildcard. Closed unmerged.
- **Port-forward on the office router to the hypervisor.** This opens the office network
itself to the internet. Rejected.
- **Move the cluster to a host with a public IP.** It would remove the tunnel, but it's a
bigger change than publishing one demo. It remains the natural step if the stack
outgrows a lab VM.
- **Keep the SSH port-forwards.** Fine for one developer, but not something you can send
to someone.
## Consequences
**Positive**
- Real hostnames and HTTPS, so PKCE works in any browser with no client-side setup.
- No new certificate handling: the labs Caddy's wildcard covers the new hosts.
- The chart stays edge-agnostic. With `keycloakUrl` empty it renders exactly as before,
so compose, CI and the `localhost` workflow are untouched.
**Negative / costs**
- **Routing lives outside the cluster**, in the Infra repo's Caddyfile. That is exactly
what #177 wanted to avoid. Adding a portal means changing three places: a NodePort in
the chart, a forward in the tunnel unit, and a host in the Caddyfile.
- **Two SSH hops in the data path.** If the hypervisor or the tunnel is down, the
portals return 502 even though the cluster is healthy.
- **One issuer string.** With `keycloakUrl` set, the `localhost` port-forward workflow
(runbook §5) can no longer log in.
- **Keycloak trusts `X-Forwarded-*`** from anything that reaches it. Today that is only
in-cluster callers and the tunnel. `KC_PROXY_TRUSTED_ADDRESSES` can narrow it if the
NodePort is ever exposed more widely.
- **The portals are public.** Anyone with the link can log in with the committed test
credentials, and with `OTP_AUTOFILL` on, no second factor stands in the way. That is
acceptable for synthetic data. Put the labs Caddy's Azure `authorize` in front of the
`big-*` hosts if the audience must be restricted.
**Follow-up**
- Runbook: `docs/runbooks/kubernetes-talos.md`, "Publishing through the labs Caddy".
- Dev-mode Keycloak generates new signing keys on every restart, and the BFF re-fetches
them at most every 5 minutes, so expect a few minutes of 401s after a Keycloak restart.
Persisting Keycloak's database (runbook §6) would remove that.
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## Publishing through the labs Caddy
Why this route and not an in-cluster edge: [ADR-0035](../architecture/adr-0035-public-access-through-the-labs-caddy.md).
The portals can be reached on real hostnames through the Caddy that already fronts
`*.labs.respellion.tech` (repo `Infra`, `infra/development/`). The chain:
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@@ -56,6 +56,7 @@ nav:
- "ADR-0032: Werkbak live refresh": architecture/adr-0032-werkbak-live-refresh.md
- "ADR-0033: Kubernetes via one Helm chart": architecture/adr-0033-kubernetes-via-one-helm-chart.md
- "ADR-0034: Caddy serves the portals": architecture/adr-0034-caddy-serves-the-portals.md
- "ADR-0035: Public access through the labs Caddy": architecture/adr-0035-public-access-through-the-labs-caddy.md
- FDS-architectuur:
- Overzicht: architecture/fds/README.md
- Componentview (L3): architecture/fds/c4-component-view.md