# 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),
[ADR-0016 (Cloudflare Tunnel public ingress)](../decisions/adr-0016-public-ingress-cloudflare-tunnel.md).

## Requirement recap

Every externally reachable service presents TLS from a **credible, trusted, non-self-signed**
authority, with certificates **auto issued and renewed** — 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 (Plex's L4 VIP name
  has its own).
- The DNS provider API token is a SOPS-encrypted secret ([07](07-security-and-secrets.md)).

## DNS-01 challenge access (OQ-4 — RESOLVED: scoped Cloudflare API token)

Certificate issuance needs programmatic write access to the zone: ACME DNS-01 must **write
`_acme-challenge` TXT records**, including for two-label-deep names like
`plex.home.keithjackson.dev`.

**Decision (OQ-4):** use a **scoped Cloudflare API token** — `Zone·DNS·Edit` limited to the
`keithjackson.dev` zone — stored **SOPS-encrypted** ([07](07-security-and-secrets.md)). With it:
- **cert-manager** solves DNS-01 by writing/removing TXT challenge records automatically (issue,
  renew — R-TLS-02), including the wildcard `*.home.keithjackson.dev` cert and internal-only
  services (R-TLS-03).
- **ExternalDNS** manages the `*.home.keithjackson.dev` records automatically ([09](09-dns-and-ingress.md),
  R-DNS-02) — no manual record editing for public services.
- **cloudflare-ddns** keeps the DNS-only `wan.` record current for WireGuard ([09](09-dns-and-ingress.md)).

**Operator prerequisite:** create the scoped token in Cloudflare and hand it over once; it is then
committed SOPS-encrypted and never touched manually again. The token is least-privilege (single zone,
DNS edit only) so its blast radius is bounded (R-SEC-02). Rotation = re-encrypt + commit.

## Renewal (R-TLS-02)

- cert-manager renews well before expiry automatically; no human action.
- Removing or rotating a certificate is a declarative change; cert-manager issues the replacement.
  The platform does not perform ACME revocation: a compromised key is handled by rotation. 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. Internal services resolve to the Gateway on the LAN.
- **Public services via the Cloudflare Tunnel (ADR-0016)** are TLS twice:
  - **Edge:** Cloudflare terminates the client's TLS with an ACM/Total TLS certificate. It is
    publicly trusted and auto-renewed (R-TLS-01/02). Universal SSL is not enough, because it covers
    only one subdomain level.
  - **Origin:** cloudflared re-encrypts to the Gateway and **validates** the Let's Encrypt wildcard,
    using the service hostname as SNI. Verification is never disabled.

  Cloudflare sees plaintext between the two legs, a trade-off accepted in ADR-0016.
- 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

Both certificates a client can meet are publicly trusted, so internal clients need no custom CA
distribution. A name Pi-hole holds a local record for ([09](09-dns-and-ingress.md)) resolves to the
internal Gateway and serves the Let's Encrypt wildcard; any other `public` name resolves to
Cloudflare's edge and serves its edge certificate.

## 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.

## Resolved
- **OQ-4** — DNS-01 via a **scoped Cloudflare API token** (`Zone·DNS·Edit`, `keithjackson.dev`),
  SOPS-encrypted; drives cert-manager DNS-01, ExternalDNS and the `wan.` record updater.
- Wildcard vs. per-service certs default — **wildcard** `*.home.keithjackson.dev` (ADR-0006).