# 13 — Cloudflare

## Summary

Cloudflare sits in front of every public request. It provides DNS
(authoritative nameservers for `myhoneydue.com`), TLS termination at
the edge, DDoS mitigation, caching, and the round-robin fan-out across
our three node IPs. We use the Free plan. TLS mode is "Flexible"
(HTTP between CF and origin). This chapter documents every Cloudflare
setting that matters.

## DNS

### Zone

`myhoneydue.com`, managed by Cloudflare. Authoritative nameservers:

```
carol.ns.cloudflare.com
ishaan.ns.cloudflare.com
```

### Records that matter

| Type | Name | Content | Proxy | Notes |
|---|---|---|---|---|
| A | `api` | 178.104.247.152 | 🟠 Proxied | hetzner1 |
| A | `api` | 178.105.32.198 | 🟠 Proxied | hetzner2 |
| A | `api` | 178.104.249.189 | 🟠 Proxied | hetzner3 |
| A | `admin` | 178.104.247.152 | 🟠 Proxied | same 3 IPs |
| A | `admin` | 178.105.32.198 | 🟠 Proxied | |
| A | `admin` | 178.104.249.189 | 🟠 Proxied | |
| A | `@` | 178.104.247.152 | 🟠 Proxied | same 3 IPs |
| A | `@` | 178.105.32.198 | 🟠 Proxied | |
| A | `@` | 178.104.249.189 | 🟠 Proxied | |

Three A records per name → Cloudflare selects one per request. With
proxying on (orange cloud), **the client never sees these IPs** — it
sees a Cloudflare edge IP. CF internally picks which of the three
origin IPs to connect to; if one fails the connection, CF retries the
next.

**TXT records for email** (Fastmail sending domain): SPF, DKIM, DMARC.
Not our immediate concern; configured by the Fastmail custom-domain
setup.

### Why three A records per name, not one

With one record pointing at hetzner1:
- Only hetzner1 sees traffic
- If hetzner1 is unreachable, everything breaks until we change DNS

With three records:
- CF chooses one origin per connection
- If one node's port :80 stops responding, CF tries the others
- Node upgrades can be done one at a time with no user impact

This is poor-man's load balancing. A Hetzner Load Balancer or Cloudflare
Load Balancer (paid) would be more sophisticated — with active health
checks and automatic failover on sub-second latency. Our DNS approach
is "good enough" for the traffic volume.

### Cloudflare's origin health checks

On Free plan, CF doesn't actively probe origins. It reacts to real
connection failures: if an origin returns 5xx repeatedly or connection
times out, CF marks it unhealthy for that edge POP for some time.

Upgrading to **Cloudflare Load Balancing** ($5/mo add-on) would enable
active health checks — explicit probes independent of traffic. Useful
when you want sub-second failover.

## TLS

### Mode: Flexible

CF Dashboard → SSL/TLS → Overview → **Flexible**.

**What this means:**
- User ↔ Cloudflare: **TLS** (HTTPS)
- Cloudflare ↔ Origin: **plaintext HTTP** (port 80)

**Why we chose it:**
- No origin cert required on the Hetzner nodes
- Zero Traefik cert-management complexity
- Fine for a site where CF terminates all user-facing TLS

**Downsides:**
- An attacker with network access between CF and Hetzner could read
  traffic. Realistically: nobody between CF's POPs and Hetzner's
  Nuremberg DC, but it's theoretically plaintext on the wire.
- MitM risk if DNS gets hijacked and traffic is routed through an
  unintended origin.

### Future: Full (strict)

The next step up is **Full (strict)**: CF verifies origin's TLS cert
and connects over HTTPS. Cloudflare provides free **Origin CA
certificates** for this: they're issued by a CF-internal CA that only
CF's own edge accepts. An attacker without a CF-signed cert can't
impersonate our origin.

Path to enable:
1. Generate Origin CA cert in CF dashboard → SSL/TLS → Origin Server
2. Download as PEM
3. Create k8s Secret `cloudflare-origin-cert`:
   ```bash
   kubectl create secret tls cloudflare-origin-cert -n honeydue \
     --cert=origin.crt --key=origin.key
   ```
4. Add `tls:` block to our Ingress:
   ```yaml
   spec:
     tls:
       - hosts: [api.myhoneydue.com]
         secretName: cloudflare-origin-cert
   ```
5. Switch CF SSL mode to Full (strict)

Trad-off: the `cloudflare-origin-cert` expires (default 15 years), so
low maintenance. **TODO** (Chapter 20).

### Edge certificate

CF provides a free edge certificate for `*.myhoneydue.com` and
`myhoneydue.com`. Auto-renewed by Cloudflare. We don't touch it.

### Always Use HTTPS

SSL/TLS → Edge Certificates → **Always Use HTTPS: On** (default).

Redirects any HTTP → HTTPS at the CF edge. Clients that hit
`http://api.myhoneydue.com/*` get 301'd to `https://...`. Origin never
sees the HTTP request.

### HSTS

**Not currently enabled.** HSTS (HTTP Strict Transport Security) sends
a header telling browsers "always use HTTPS for this domain." Once set
with long `max-age`, it's **permanent** until it expires — if we later
misconfigure TLS, HSTS-enabled browsers refuse to connect at all.

Enabling HSTS is a TODO but requires confidence in our TLS stability.
Not tonight.

## DDoS mitigation

CF's Free plan includes basic DDoS protection:
- Volumetric attacks absorbed at the edge
- Obvious bot patterns blocked (known-bad user agents, headless browsers
  doing suspicious things)

Under a large attack, CF might:
- Insert a "checking your browser" JavaScript challenge (the ~5-second
  "Cloudflare is checking your browser" page)
- Rate-limit by IP

Under a sustained, sophisticated attack we might need:
- CF Pro plan ($20/mo) for more rule customization
- Enterprise plan for negotiated protection
- Extra measures like Cloudflare Magic Transit

So far, not needed.

## Caching

Default CF caching:
- Static assets (CSS, JS, images) cached aggressively based on extension
- HTML pages honored per `Cache-Control` headers from origin
- JSON API responses typically not cached (no `Cache-Control: public`)

Our Go API doesn't set `Cache-Control: public` on any endpoint, so CF
treats them as uncacheable. Every API call reaches origin.

If we wanted to cache certain endpoints (e.g., public lookup tables):
```go
c.Response().Header().Set("Cache-Control", "public, max-age=300")
```
And CF will cache for 5 minutes.

## Firewall rules at CF

CF Dashboard → Security → WAF. On Free tier:
- Managed rules: a small free allowlist of "obvious-attack" patterns
- Custom rules: limited (5 on Free, 20 on Pro)

We have **no custom rules defined** currently. The managed ruleset
covers:
- SQL injection attempts in query strings
- Known-vulnerable bot User-Agents
- XSS attempts in common parameters

## Rate limiting

CF Free: **10,000 requests per 10 minutes per IP for free rules** (we
haven't configured any). The API itself should have rate limits for
sensitive endpoints; we don't rely on CF for that.

## What CF does NOT do for us

- **Authenticate users** — our app does
- **Authorize requests** — our app does
- **Encrypt pod-to-pod traffic** — nothing Cloudflare can help with
- **Backup origin data** — CF caches but doesn't store copies
  persistently

## Turnstile / bot management

Not enabled. If we start seeing account-creation spam, Cloudflare
Turnstile (free) would be a good addition — a CAPTCHA replacement that
doesn't require user interaction for most traffic.

## Origin IP protection

CF proxying (orange cloud) is the primary protection of our origin IPs.
When proxying is on:
- DNS queries return CF edge IPs, never origin
- HTTP/HTTPS traffic goes through CF

However, our origin IPs **can leak** via:
- Email sending (if the app ever sent email directly from the origin IP)
  — we use Fastmail so this isn't an issue
- Outbound connections (our pods connect out to Neon, B2, Fastmail from
  the nodes' public IPs; those IPs appear in external logs)
- Historical DNS records (services like SecurityTrails log historical
  DNS; if we ever had unproxied A records, attackers can look them up)

**If origin IPs leak**, attackers can bypass CF's protection by
connecting directly to node IPs. Current mitigation:
- UFW only allows :80/:443 from anywhere
- Our app has no ports bound to the public IP

**Future** (Chapter 20): UFW rule to allow :80/:443 only from CF IP
ranges. Prevents direct-connect bypass entirely.

## Cloudflare IP ranges (used in Traefik trustedIPs)

From [cloudflare.com/ips](https://www.cloudflare.com/ips/):

IPv4 ranges:
```
173.245.48.0/20
103.21.244.0/22
103.22.200.0/22
103.31.4.0/22
141.101.64.0/18
108.162.192.0/18
190.93.240.0/20
188.114.96.0/20
197.234.240.0/22
198.41.128.0/17
162.158.0.0/15
104.16.0.0/13
104.24.0.0/14
172.64.0.0/13
131.0.72.0/22
```

IPv6 ranges:
```
2400:cb00::/32
2606:4700::/32
2803:f800::/32
2405:b500::/32
2405:8100::/32
2a06:98c0::/29
2c0f:f248::/32
```

These are used in two places:
1. **Traefik `forwardedHeaders.trustedIPs`** — we already have this
   configured (Chapter 6)
2. **UFW `allow 80/tcp from <cf-range>`** — NOT configured (TODO)

CF occasionally adds new ranges. If a future CF range isn't in our
list, we'd either trust unknown IPs (if lax) or reject legitimate CF
traffic (if strict). The canonical source is the public API:

```bash
curl -sS https://www.cloudflare.com/ips-v4
curl -sS https://www.cloudflare.com/ips-v6
```

## API token for programmatic changes

If we automate DNS changes (e.g., adding new subdomain on deploy),
we'd need a CF API token with `Zone:DNS:Edit` scope for the
`myhoneydue.com` zone.

Currently not automated; DNS is managed in the CF dashboard by hand.

## Cost

**$0/mo**. Free plan covers everything we use. Paid plans add features
we don't need yet:

| Feature | Free | Pro ($20) | Business ($200) |
|---|---|---|---|
| DNS + proxying | ✓ | ✓ | ✓ |
| Basic DDoS | ✓ | ✓ | ✓ |
| SSL (edge + Flexible + Full + Full strict) | ✓ | ✓ | ✓ |
| WAF managed rules | ✓ (limited) | ✓ (more) | ✓ (all) |
| Custom firewall rules | 5 | 20 | 100 |
| Page Rules | 3 | 20 | 50 |
| Image Resizing | no | no | ✓ |
| Load Balancing | no | $5/mo add-on | ✓ |

We'd consider Pro ($20/mo) if:
- We needed a custom WAF rule beyond the 5-rule limit
- We wanted Image Resizing for user-uploaded photos

Neither is needed today.

## Operator cheat sheet

```bash
# Query current CF-served DNS
dig +short @1.1.1.1 api.myhoneydue.com    # returns CF edge IPs when proxied

# Query our origin directly (bypass CF)
curl -sS -H "Host: api.myhoneydue.com" http://178.104.247.152/api/health/

# Check CF headers (confirm you're going through CF)
curl -sS -I https://api.myhoneydue.com/api/health/ | grep -i cf-

# Purge CF cache (requires API token)
curl -X POST \
  -H "Authorization: Bearer $CF_TOKEN" \
  -H "Content-Type: application/json" \
  "https://api.cloudflare.com/client/v4/zones/<zone_id>/purge_cache" \
  -d '{"purge_everything":true}'
```

## References

- [Cloudflare IP ranges][cf-ips]
- [Cloudflare SSL modes explained][cf-ssl]
- [Origin CA certificates][cf-origin-ca]
- [Cloudflare DNS best practices][cf-dns]

[cf-ips]: https://www.cloudflare.com/ips/
[cf-ssl]: https://developers.cloudflare.com/ssl/origin-configuration/ssl-modes/
[cf-origin-ca]: https://developers.cloudflare.com/ssl/origin-configuration/origin-ca/
[cf-dns]: https://developers.cloudflare.com/dns/
