boma/docs/decisions/024-reverse-proxy.md

# ADR-024 — Reverse proxy: Caddy (ACME — HTTP-01 public, DNS-01 private)

## Status

Accepted (2026-06-14). Amends the soft Traefik assumption carried by the roadmap
(Phase-2 step 5) and ADR-017 prose; those are updated to read "Caddy (ADR-024)".

> **Cert method follows exposure (revised 2026-06-14, M4a).** The cert *challenge*
> depends on whether a host is publicly reachable: **public hosts** (askari) use
> **HTTP-01** with **vanilla Caddy** — simplest, no plugin; **mesh/LAN-only cluster
> services** (no public A-record) need **DNS-01** (the M1 Gandi capability), since they
> can't satisfy HTTP-01. The DNS-01 path is **deferred to Phase 2**: the `caddy-dns/gandi`
> plugin did not create the ACME TXT records on askari despite a verified-valid token
> (and Hetzner IPs are 403'd by Google's Go module infra, blocking the on-host custom
> build) — both to be sorted when the cluster's private services actually need DNS-01.
> The body below describes the DNS-01 design; askari (M4a) ships on HTTP-01.

## Context

boma needs a reverse proxy to front its services with TLS. ADR-002 requires every
service to sit behind a proxy with authentication before it is reachable; ADR-007/M1
delivers a `*.boma.<domain>` wildcard cert via ACME DNS-01 against Gandi — the only
viable cert path for mesh/LAN-only services that cannot satisfy HTTP-01 (no public
A-record to point at).

The roadmap (Phase-2, step 5) and ADR-017 prose assumed **Traefik + Authentik** as the
auth-and-proxy pair without an ADR ever pinning Traefik. On closer inspection:

- Traefik's headline feature is **dynamic Docker-label discovery** — it discovers and
  routes services automatically from container labels without any static config.
- boma already renders *all* config from Ansible templates and the `group_vars` catalog
  (ADR-004). That makes dynamic label discovery a disadvantage: a service that is not in
  the catalog does not exist (CLAUDE.md), so any route that Traefik auto-discovers
  outside the catalog would be unaudited.
- The first reverse-proxy instance is needed on `askari` for M4 (NetBird), a host where
  `docker_hosts` patterns are being established under off-site/VPS constraints, not a
  full Proxmox cluster with many services.

No production investment in Traefik config has been made; the decision can be made
cleanly here.

## Decision

boma's reverse proxy is **Caddy**.

### 1. Rationale for Caddy over Traefik

1. Traefik's dynamic label discovery is wasted — boma renders config from the catalog;
   Caddy's static Caddyfile maps naturally to "render from templates" (ADR-004).
2. Caddy's Caddyfile is simple to template with `ansible.builtin.template`; one file,
   one `ansible_managed` header, no side-channel label state.
3. **Automatic HTTPS** via ACME DNS-01: the `caddy-dns/gandi` plugin satisfies the
   Gandi DNS-01 challenge, which is the only cert path for services with no public
   A-record (ADR-007/M1 wildcard strategy).
4. Far simpler for a solo operator: no dashboard-as-a-service, no routing-rule DSL,
   no dynamic config files to reconcile.
5. `forward_auth` to Authentik is a first-class Caddy directive — the planned
   Authentik auth story (ADR-002) is preserved without Traefik as the middleman.

### 2. Custom image (DNS-01 path only — Phase 2)

> Applies only to the **DNS-01** path, which is **deferred to Phase 2** (see the Status
> note). M4a ships **vanilla `caddy:2`** on askari (HTTP-01) — no custom image.

Caddy's official Docker image does not include third-party DNS plugins. The `caddy-dns/gandi`
plugin must be compiled in via `xcaddy`. When the cluster's mesh/LAN-only services need
DNS-01, boma builds a custom image:

```
FROM caddy:builder AS builder
RUN xcaddy build --with github.com/caddy-dns/gandi

FROM caddy:latest
COPY --from=builder /usr/bin/caddy /usr/bin/caddy
```

That image would be maintained as a boma artifact (Forgejo registry, pinned digest in the
Compose template) — the cost of the Gandi DNS-01 path. (On askari this approach hit two
blockers, so DNS-01 is deferred; see the Status note.)

### 3. Deployment scope

The first Caddy instance runs on `askari` (M4a), serving a test vhost over HTTP-01 to
prove the proxy + ACME path. It fronts the NetBird stack in **M4b** (when the
`netbird` coordinator role is built). The pattern generalises to the Proxmox cluster in
Phase 2 when services multiply.

### 4. Authentik integration (deferred)

`forward_auth` to Authentik is deferred to Phase 2 (when Authentik is deployed on the
cluster). The Caddyfile template will carry a placeholder comment. No Traefik-Authentik
middleware migration is required.

## Consequences

- **Roadmap Phase-2 step 5** is updated from "Authentik + Traefik" to "Authentik +
  Caddy (ADR-024)".
- **ADR-017 prose** that mentioned Traefik is updated to read "Caddy (ADR-024)".
- M4a (public hosts, HTTP-01) runs **vanilla `caddy:2`** — no custom image. **If/when**
  the Phase-2 DNS-01 path lands, a custom Caddy image (`xcaddy` + `caddy-dns/gandi`) must
  be built, pushed to the Forgejo registry, and kept current (plugin + base image updates).
- Caddyfile config is rendered by Ansible from `group_vars` — consistent with ADR-004
  and easier to review than distributed container labels.
- `forward_auth` to Authentik is available when Authentik is deployed; no extra
  middleware layer required.
- The `proxy` concern tag (already in `tests/tags.yml`) covers Caddy config tasks.

## What was ruled out

- **Traefik** — dynamic label discovery is a mismatch for boma's catalog-rendered
  config model (ADR-004); more complex for a solo operator; no prior investment to
  protect.
- **nginx / HAProxy** — no built-in ACME; require a separate ACME client (certbot,
  acme.sh) adding operational surface; Caddy's integrated ACME is simpler.
- **NetBird's bundled TLS** — NetBird's management UI can serve its own TLS, but that
  doesn't generalise; a real proxy separates concerns and applies to every service.

## Related

- ADR-002 — services behind a proxy with authentication (the requirement this satisfies).
- ADR-004 — Docker & Compose model (template-rendered config, catalog-driven).
- ADR-007 / M1 — Gandi DNS-01 ACME path (the TLS strategy Caddy implements).
- ADR-016 — NetBird (M4 is the first deployment of this proxy).
- ADR-017 — service-UI verification; forward_auth to Authentik is the future auth story.