# 00 — Overview

## Summary

honeyDue runs on a three-node Kubernetes cluster managed by K3s, fronted by
Cloudflare, and backed by a managed Postgres (Neon), S3-compatible object
storage (Backblaze B2), and a self-hosted container registry (Gitea). The
application consists of a Go REST API, a Next.js admin panel, and a
background worker process using Redis-backed queues. Traefik handles HTTP
ingress and path-based routing. The whole stack fits in about 1 GB of RAM
across the three nodes with plenty of headroom.

This chapter is the map. Everything here is expanded in a later chapter.

## Architecture at a glance

```mermaid
flowchart TB
    subgraph Internet
        Browser[End-user browser / mobile client]
    end

    subgraph CF[Cloudflare]
        CFEdge[Edge POP<br/>TLS terminates here]
    end

    Browser -- HTTPS :443 --> CFEdge

    subgraph Hetzner[Hetzner Cloud — Nuremberg nbg1]
        direction LR
        subgraph H1[hetzner1<br/>178.104.247.152]
            T1[Traefik<br/>:80/:443 hostNet]
            A1[api pod]
            W1[worker pod]
        end
        subgraph H2[hetzner2<br/>178.105.32.198]
            T2[Traefik<br/>:80/:443 hostNet]
            A2[api pod]
            R1[redis pod<br/>PVC]
        end
        subgraph H3[hetzner3<br/>178.104.249.189]
            T3[Traefik<br/>:80/:443 hostNet]
            A3[api pod]
            AD1[admin pod]
        end
    end

    CFEdge -- HTTP :80<br/>DNS round-robin --> T1
    CFEdge -- HTTP :80 --> T2
    CFEdge -- HTTP :80 --> T3

    T1 & T2 & T3 -.Ingress routes by<br/>Host header.-> A1
    T1 & T2 & T3 -.-> AD1
    A1 & A2 & A3 -.-> R1

    subgraph External[Managed services]
        Neon[(Neon Postgres<br/>AWS us-east-1)]
        B2[(Backblaze B2<br/>us-east-005)]
        FM[Fastmail SMTP]
        Gitea[Gitea Registry<br/>gitea.treytartt.com]
    end

    A1 & A2 & A3 -- SSL --> Neon
    W1 -- SSL --> Neon
    A1 & A2 & A3 -- HTTPS --> B2
    W1 -- SMTP :587 --> FM
    H1 & H2 & H3 -. image pull .-> Gitea
```

### ASCII fallback

```
                         ┌─────────────────────┐
                         │     End user        │
                         └──────────┬──────────┘
                                    │ HTTPS :443
                                    ▼
                         ┌─────────────────────┐
                         │  Cloudflare edge    │ TLS terminates here
                         │  (SSL = Flexible)   │
                         └──────────┬──────────┘
                       HTTP :80 round-robin
                  ┌─────────────┼─────────────┐
                  ▼             ▼             ▼
     ┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐
     │   hetzner1      │ │   hetzner2      │ │   hetzner3      │
     │ 178.104.247.152 │ │ 178.105.32.198  │ │ 178.104.249.189 │
     │ Traefik :80/443 │ │ Traefik :80/443 │ │ Traefik :80/443 │
     │  api   worker   │ │  api   redis    │ │  api   admin    │
     └─────────┬───────┘ └─────────┬───────┘ └─────────┬───────┘
               │                   │                   │
               └──────── Kubernetes overlay ───────────┘
                                   │
     ┌─────────────────────────────┴──────────────────────────────┐
     │                                                             │
     ▼                      ▼                    ▼                 ▼
┌─────────┐          ┌─────────────┐     ┌──────────┐    ┌───────────────┐
│  Neon   │          │ Backblaze B2│     │ Fastmail │    │ Gitea Registry│
│Postgres │          │   uploads   │     │   SMTP   │    │   image pull  │
└─────────┘          └─────────────┘     └──────────┘    └───────────────┘
```

## The stack, one layer at a time

### Layer 0 — Hardware

Three Hetzner Cloud CX33 instances (4 vCPU, 8 GB RAM, 80 GB NVMe SSD) in
Hetzner's Nuremberg (nbg1) datacenter. Each node is $7.99/mo (April 2026
pricing), totaling ~$24/mo. See [Chapter 1](./01-infrastructure.md).

### Layer 1 — Operating system

Ubuntu 24.04.3 LTS. Each node has:
- SSH on port 22, key-only auth, `deploy` user with NOPASSWD sudo
- `ufw` firewall with strict default-deny-incoming; specific ports allowed
  per Chapter 4
- Sysctl override `net.ipv4.ip_unprivileged_port_start=0` so non-root
  containers can bind privileged ports (needed for Traefik to serve :80/:443)

### Layer 2 — Container runtime

`containerd` v2.2.2 (bundled with K3s). Docker was previously installed from
the Swarm era but is now disabled. containerd is Kubernetes' reference
runtime and has a smaller footprint than Docker's full stack.

### Layer 3 — Orchestrator

K3s v1.34.6 in HA mode. All 3 nodes are `control-plane,etcd` (Raft quorum
of 3 — can tolerate one node failure). K3s is a minimal Kubernetes
distribution from Rancher Labs (now Suse): single-binary, embedded etcd
instead of a separate etcd cluster, sane defaults for small installations.
See [Chapter 2](./02-orchestrator-choice.md) for why k3s over full Kubernetes
or Docker Swarm.

### Layer 4 — Cluster networking

- **Flannel VXLAN** for pod-to-pod overlay (default on K3s). VXLAN tunnels
  pod traffic over UDP port 8472 between nodes.
- **CoreDNS** for service discovery (what pods call `api` or `redis` to
  reach each other).
- **kube-proxy** in IPVS mode for ClusterIP → pod routing.

[Chapter 3](./03-networking.md) walks through a single request to show
every hop.

### Layer 5 — Ingress

**Traefik v3** as a DaemonSet with `hostNetwork: true`. Each node has a
Traefik pod that binds directly to the node's public :80 and :443. No
`servicelb`, no Hetzner Load Balancer — Cloudflare round-robins the three
node IPs in DNS and any node can serve any request. See
[Chapter 6](./06-traefik-ingress.md).

### Layer 6 — Edge / CDN

Cloudflare Free plan. Proxied A records for `api.myhoneydue.com`,
`admin.myhoneydue.com`, and `myhoneydue.com` each point at all three node
IPs. Edge handles TLS termination (SSL=Flexible), DDoS protection, caching
for static assets, and traffic failover if a node becomes unreachable.
See [Chapter 13](./13-cloudflare.md).

### Layer 7 — Application services

| Service | Type | Replicas | Image |
|---|---|---|---|
| `api` | Go (Echo, GORM) | 3 | `gitea.treytartt.com/admin/honeydue-api:<sha>` |
| `admin` | Next.js 16 | 1 | `gitea.treytartt.com/admin/honeydue-admin:<sha>` |
| `worker` | Go (Asynq) | 1 | `gitea.treytartt.com/admin/honeydue-worker:<sha>` |
| `redis` | redis:7-alpine | 1 | Docker Hub |

See [Chapter 7](./07-services.md).

### Layer 8 — External dependencies

- **Neon Postgres** (Launch plan) — `honeyDue` database
- **Backblaze B2** — `honeyDueProd` bucket for user uploads
- **Fastmail SMTP** — transactional email
- **Gitea** (self-hosted at `gitea.treytartt.com`) — container registry
- **Cloudflare** — DNS, TLS, CDN

See [Chapter 8](./08-database.md), [9](./09-storage.md), and
[11](./11-registry.md).

## What's deliberately absent

- **TLS at origin.** Cloudflare terminates TLS at the edge and talks HTTP
  on port 80 to the nodes. This is "Flexible SSL" in Cloudflare terminology.
  It's the simplest setup; we have a TODO to upgrade to "Full (strict)" with
  Cloudflare Origin CA certs ([Chapter 13](./13-cloudflare.md), §Future).
- **Hetzner Load Balancer.** We save the $8.49/mo by having Cloudflare
  round-robin across node IPs directly. If any node is unresponsive,
  Cloudflare's own origin health checks will route around it within 30s.
- **Push notifications.** APNs (iOS) and FCM (Android) are *configured off*
  until we have Apple Developer / Google Play accounts. The env vars are
  set to sentinel values that let the Go app boot; `FEATURE_PUSH_ENABLED=false`
  gates all call sites.
- **In-cluster Prometheus / Grafana.** Self-hosted Prometheus-compatible
  metrics + tracing + dashboards live **outside** the k3s cluster on
  `88oakappsUpdate` (the same Linode VPS that hosts PostHog), reached
  via `https://obs.88oakapps.com` (Cloudflare-fronted, bearer-gated).
  A `vmagent` sidecar in the honeydue namespace scrapes the api Pods
  and remote-writes out. This frees ~700 MB of cluster RAM and means
  observability survives a k3s control-plane incident. See
  [Chapter 15](./15-observability.md).
- **Alerting.** No PagerDuty, Slack hooks, or pages-on-error wired up
  yet. Histograms are flowing into Grafana — alert rules on top of them
  is the next add. See [Chapter 15 — Future](./15-observability.md).
- **Automated backups of Redis state.** Redis is configured with AOF
  (append-only file) persistence, but the PVC is only on one node. Redis
  holds only cache + Asynq queue state; losing it re-populates on first
  request / next cron tick. Not critical.
- **Admin panel basic auth (Traefik middleware).** In-app admin login is
  enabled; the extra Traefik-layer basic auth the scaffold supports is not
  currently attached.

## The deployment pipeline in one paragraph

Changes to application code are built on your workstation by
`docker buildx build --platform linux/amd64 --push`, which cross-compiles
from arm64 (Apple Silicon) to amd64 (Hetzner nodes) and pushes directly to
`gitea.treytartt.com`. Manifests live in `deploy-k3s/manifests/`; they
reference image tags by git short SHA. `kubectl apply -f` rolls the new
image in with `maxUnavailable: 0, maxSurge: 1` — one new pod at a time,
old one stays up until new is healthy. Service discovery by Kubernetes
DNS means `api` and `admin` hostnames always resolve to live backing pods;
traffic shifts the moment a new pod passes its readiness probe.
[Chapter 14](./14-deployment-process.md) walks through a complete deploy.

## What we *used* to have (the short version)

Up until 2026-04-24 this stack ran on **Docker Swarm** on the same three
Hetzner boxes. It worked, but the Docker libnetwork service-discovery
layer has a bug in the 29.x line ([moby/moby#52265][moby-52265]) that
leaves stale DNS A-records behind when tasks migrate between nodes. We
hit it: the admin panel returned 502s for ~50% of requests through
Cloudflare because Caddy (our previous reverse proxy) was dialing a ghost
IP that had since been recycled to the Dozzle log viewer. We spent four
hours trying increasingly clever workarounds (dnsrr vs VIP,
`dynamic a` DNS refresh, global mode, host-mode ports, host.docker.internal,
hardcoded node IPs) before concluding that libnetwork state corruption
survives every non-nuclear fix.

The full autopsy is in [Chapter 19 — Swarm Postmortem](./19-postmortem-swarm.md).
K3s uses CoreDNS and has no libnetwork history; the bug class doesn't
exist there.

[moby-52265]: https://github.com/moby/moby/issues/52265