# ADR-001 — Architecture overview

## Status

Accepted (2026-05-30)

## Context

This document describes the overall architecture of the homelab infrastructure
and the boundaries of what this Ansible monorepo manages.

## Infrastructure

- **Hypervisor**: Proxmox cluster (2+ nodes)
- **Guest OS**: Debian 13 (all managed hosts)
- **Scale**: 2–5 VMs, small fleet — treated as individuals, not cattle
- **Control node**: `ubongo` — a dedicated always-on **physical** x86-64 machine
  **outside** the cluster. Ansible runs from here. It cannot be created by the
  Terraform it hosts, so it is provisioned manually (see ADR-015 and
  `docs/runbooks/new-host.md`).

## What this repo manages

| Layer              | Managed by         | Notes                                      |
|--------------------|--------------------|--------------------------------------------|
| VM existence       | Terraform (`terraform/`) | Clones the cloud-init template; `ubongo` (control node) is a physical box outside the cluster, the one manual exception (see ADR-009/ADR-015) |
| Internal DNS records | Ansible `dns` role | Internal zone rendered from inventory (see ADR-007/009) |
| OS baseline        | Ansible `base` role | Users, SSH, firewall, updates, audit       |
| Docker runtime     | Ansible `docker_host` role | Engine, daemon config, log driver  |
| Service deployment | Ansible per-service roles | Compose rendered from templates      |
| Secrets            | Ansible Vault      | Encrypted `vault.yml` files in repo        |

The Terraform↔Ansible boundary and handoff are defined in ADR-009. This table
describes the *intended* design — see STATUS.md for what is actually built.

## Host groups

```
all
├── control           # ubongo — physical control node outside the cluster; baseline config only, runs no services
├── docker_hosts      # VMs running Docker services (most hosts)
├── proxmox_hosts     # Proxmox nodes themselves (limited management scope)
└── offsite_hosts     # askari (off-site Hetzner) — NetBird coordinator + external watchdog
```

The `control` group holds the single manually-provisioned control node; it is
managed for baseline config (SSH, firewall, updates) but never runs the
`docker_host` role. The `offsite_hosts` group holds `askari`, the off-site Hetzner
host — also manually provisioned (ADR-016), managed for baseline config plus the
`netbird_coordinator` service role. Proxmox nodes are managed only for basic baseline tasks (SSH).
Proxmox configuration itself (storage, clustering, networking)
is out of scope.

## Service interaction model

Services run as Docker containers on one or more `docker_hosts`. Where services
need to interact, they do so via:

- Docker networks (same host)
- Internal DNS / hostname resolution (cross-host)
- Explicitly defined published ports (external access)

All Compose files are rendered by Ansible from Jinja2 templates. No hand-edited
Compose files exist on hosts — they are always regenerated on deploy.

## Decision

This architecture prioritises:
- **Simplicity**: few moving parts, no orchestration layer (no Kubernetes, no Swarm)
- **Reproducibility**: any host can be rebuilt from scratch via Ansible
- **Legibility**: a human reading the repo can understand what runs where

## Consequences

Drawn from the boundaries this ADR already states:

- The small fleet (2–5 VMs) is treated as individuals, not cattle (per Infrastructure),
  and forgoing an orchestration layer is the cost of the simplicity priority (per
  Decision).
- The control node `ubongo` cannot be created by the Terraform it hosts, so it is
  provisioned manually — the one documented exception to Terraform-owned VM existence
  (per Infrastructure / Host groups; ADR-009, ADR-015).
- Management scope is deliberately bounded: Proxmox configuration itself (storage,
  clustering, networking) is out of scope, and the `control` group never runs the
  `docker_host` role (per Host groups).
- Compose files are always regenerated by Ansible on deploy; no hand-edited Compose
  files exist on hosts (per Service interaction model).
- The "What this repo manages" table describes the *intended* design — STATUS.md
  records what is actually built (per that section).