# 08 — TLS & Certificates

Serves: **R-TLS-01/02/03**, **R-DNS-01**. Related: [ADR-0006 (cert-manager + Let's Encrypt)](../decisions/adr-0006-tls-cert-manager-letsencrypt.md).

## Requirement recap

Every externally reachable service presents TLS from a **credible, trusted, non-self-signed**
authority, with certificates **auto issued, renewed, and revoked** — including for **internal-only**
services (R-TLS-01/02/03).

## Solution: cert-manager + Let's Encrypt via DNS-01

- **cert-manager** runs in the cluster and manages the full certificate lifecycle.
- **Let's Encrypt** is the trusted, non-self-signed CA (publicly trusted; free; automatable) —
  satisfies R-TLS-01.
- **ACME DNS-01 challenge** against the `keithjackson.dev` DNS zone (Cloudflare or equivalent, per
  OQ-4). DNS-01 is the key choice because it validates domain control **without exposing the service
  publicly** — so internal-only services get real, trusted certs (R-TLS-03), and **wildcard**
  certificates (`*.home.keithjackson.dev`) are possible.

## Issuance model

- A `ClusterIssuer` for Let's Encrypt production (and one for staging, used during bring-up to avoid
  rate limits).
- Certificates are requested declaratively — either a **wildcard** `*.home.keithjackson.dev` cert
  shared by the Gateway, or **per-service** certs, decided per ADR-0006. Recommendation: a wildcard
  cert for `*.home.keithjackson.dev` terminated at the Gateway simplifies onboarding (a new service
  needs no new cert), with per-service certs available where isolation warrants.
- The DNS provider API token is a SOPS-encrypted secret ([07](07-security-and-secrets.md)).

## DNS-01 challenge access (OQ-4 — the one open item)

Cloudflare already has a wildcard `*.keithjackson.dev` → public-IP record. **That covers
reachability but not certificate issuance**: ACME DNS-01 requires cert-manager to **write
`_acme-challenge` TXT records**, and the existing wildcard does not match two-label-deep names like
`plex.home.keithjackson.dev`. So a **challenge-access decision is still required**:

- **Option A — scoped Cloudflare API token** (Zone·DNS·Edit for `keithjackson.dev`), stored
  SOPS-encrypted ([07](07-security-and-secrets.md)). cert-manager writes TXT challenges and
  ExternalDNS manages the `*.home.keithjackson.dev` records — **fully automated**. *Recommended
  (simplest).*
- **Option B — acme-dns delegation**: a one-time `_acme-challenge` **CNAME** in Cloudflare points to
  an in-cluster acme-dns server; cert-manager writes only to acme-dns, so **no standing Cloudflare
  credential** lives in the cluster. More moving parts; public `*.home` records then need the
  one-time wildcard record instead of ExternalDNS.

Either option supports the wildcard `*.home.keithjackson.dev` cert and internal-only issuance
(R-TLS-03). This is the remaining blocker for the TLS/DNS workstream (Phase 2).

## Renewal & revocation (R-TLS-02)

- cert-manager renews well before expiry automatically; no human action.
- Revocation: removing/rotating a certificate is a declarative change; cert-manager handles
  issuance of replacements. Expiry monitoring is an alert condition ([10](10-observability-and-alerting.md), R-OBS-04).

## Where TLS terminates

- **North-south**: at the **Gateway API** listener (implemented by Cilium, [09](09-dns-and-ingress.md)),
  using the cert-manager-issued cert. Public services are reached via the edge router forwarding to
  the Gateway; internal services resolve to the Gateway on the LAN.
- Internal service-to-service traffic relies primarily on network policy for security; mTLS between
  workloads is **optional** future hardening (could be added via Cilium/service mesh) and is not a
  launch requirement — record as a possible future ADR.

## Trust chain for internal clients

Because certs come from Let's Encrypt (publicly trusted), internal clients trust them with no custom
CA distribution. Split-horizon DNS ([09](09-dns-and-ingress.md)) resolves
`<service>.home.keithjackson.dev` to the internal Gateway while the same trusted cert is served.

## Acceptance gates
- `https://<service>.home.keithjackson.dev` serves a valid, non-self-signed, unexpired certificate
  (verified by an external TLS checker), including for internal-only services.
- Certificates renew automatically ahead of expiry with no manual step (observed across a renewal).
- Certificate expiry and issuance failures raise alerts.
- Onboarding a new service requires no manual certificate step.

## Open questions
- **OQ-4** — DNS-01 challenge access: **Option A (scoped Cloudflare API token, recommended)** vs
  **Option B (acme-dns delegation)**. Provider is Cloudflare (confirmed). This is the only item still
  blocking Phase 2 TLS.
- Wildcard vs. per-service certs default — **resolved: wildcard** `*.home.keithjackson.dev` (ADR-0006).