sjat
d10f6de84b
Adds ADR-024 pinning Caddy (xcaddy + caddy-dns/gandi) as boma's reverse proxy, superseding the soft Traefik assumption in the roadmap and ADR-017 prose. Updates CLAUDE.md Further reading table and ROADMAP.md Phase-2 step 5. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
107 lines
5 KiB
Markdown
107 lines
5 KiB
Markdown
# ADR-024 — Reverse proxy: Caddy with ACME DNS-01 (Gandi)
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## Status
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Accepted (2026-06-14). Amends the soft Traefik assumption carried by the roadmap
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(Phase-2 step 5) and ADR-017 prose; those are updated to read "Caddy (ADR-024)".
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## Context
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boma needs a reverse proxy to front its services with TLS. ADR-002 requires every
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service to sit behind a proxy with authentication before it is reachable; ADR-007/M1
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delivers a `*.boma.<domain>` wildcard cert via ACME DNS-01 against Gandi — the only
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viable cert path for mesh/LAN-only services that cannot satisfy HTTP-01 (no public
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A-record to point at).
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The roadmap (Phase-2, step 5) and ADR-017 prose assumed **Traefik + Authentik** as the
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auth-and-proxy pair without an ADR ever pinning Traefik. On closer inspection:
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- Traefik's headline feature is **dynamic Docker-label discovery** — it discovers and
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routes services automatically from container labels without any static config.
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- boma already renders *all* config from Ansible templates and the `group_vars` catalog
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(ADR-004). That makes dynamic label discovery a disadvantage: a service that is not in
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the catalog does not exist (CLAUDE.md), so any route that Traefik auto-discovers
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outside the catalog would be unaudited.
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- The first reverse-proxy instance is needed on `askari` for M4 (NetBird), a host where
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`docker_hosts` patterns are being established under off-site/VPS constraints, not a
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full Proxmox cluster with many services.
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No production investment in Traefik config has been made; the decision can be made
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cleanly here.
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## Decision
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boma's reverse proxy is **Caddy**.
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### 1. Rationale for Caddy over Traefik
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1. Traefik's dynamic label discovery is wasted — boma renders config from the catalog;
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Caddy's static Caddyfile maps naturally to "render from templates" (ADR-004).
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2. Caddy's Caddyfile is simple to template with `ansible.builtin.template`; one file,
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one `ansible_managed` header, no side-channel label state.
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3. **Automatic HTTPS** via ACME DNS-01: the `caddy-dns/gandi` plugin satisfies the
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Gandi DNS-01 challenge, which is the only cert path for services with no public
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A-record (ADR-007/M1 wildcard strategy).
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4. Far simpler for a solo operator: no dashboard-as-a-service, no routing-rule DSL,
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no dynamic config files to reconcile.
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5. `forward_auth` to Authentik is a first-class Caddy directive — the planned
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Authentik auth story (ADR-002) is preserved without Traefik as the middleman.
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### 2. Custom image
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Caddy's official Docker image does not include third-party DNS plugins. The `caddy-dns/gandi`
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plugin must be compiled in via `xcaddy`. boma builds a custom image:
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```
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FROM caddy:builder AS builder
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RUN xcaddy build --with github.com/caddy-dns/gandi
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FROM caddy:latest
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COPY --from=builder /usr/bin/caddy /usr/bin/caddy
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```
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This image is maintained as a boma artifact (Forgejo registry, pinned digest in the
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Compose template). It is the cost of the Gandi DNS-01 path — unavoidable regardless of
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proxy choice.
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### 3. Deployment scope
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The first Caddy instance fronts the NetBird stack on `askari` (M4). The pattern
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generalises to the Proxmox cluster in Phase 2 when services multiply.
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### 4. Authentik integration (deferred)
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`forward_auth` to Authentik is deferred to Phase 2 (when Authentik is deployed on the
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cluster). The Caddyfile template will carry a placeholder comment. No Traefik-Authentik
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middleware migration is required.
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## Consequences
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- **Roadmap Phase-2 step 5** is updated from "Authentik + Traefik" to "Authentik +
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Caddy (ADR-024)".
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- **ADR-017 prose** that mentioned Traefik is updated to read "Caddy (ADR-024)".
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- A custom Caddy image (`xcaddy` + `caddy-dns/gandi`) must be built, pushed to the
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Forgejo registry, and kept current (plugin + base image updates).
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- Caddyfile config is rendered by Ansible from `group_vars` — consistent with ADR-004
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and easier to review than distributed container labels.
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- `forward_auth` to Authentik is available when Authentik is deployed; no extra
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middleware layer required.
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- The `proxy` concern tag (already in `tests/tags.yml`) covers Caddy config tasks.
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## What was ruled out
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- **Traefik** — dynamic label discovery is a mismatch for boma's catalog-rendered
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config model (ADR-004); more complex for a solo operator; no prior investment to
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protect.
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- **nginx / HAProxy** — no built-in ACME; require a separate ACME client (certbot,
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acme.sh) adding operational surface; Caddy's integrated ACME is simpler.
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- **NetBird's bundled TLS** — NetBird's management UI can serve its own TLS, but that
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doesn't generalise; a real proxy separates concerns and applies to every service.
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## Related
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- ADR-002 — services behind a proxy with authentication (the requirement this satisfies).
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- ADR-004 — Docker & Compose model (template-rendered config, catalog-driven).
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- ADR-007 / M1 — Gandi DNS-01 ACME path (the TLS strategy Caddy implements).
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- ADR-016 — NetBird (M4 is the first deployment of this proxy).
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- ADR-017 — service-UI verification; forward_auth to Authentik is the future auth story.
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