# Architecture

## Request Flow

The following describes the path a request takes from an external client to a backend service and back:

### Proxied Service (e.g., `app.example.com`)

1. An external client sends an HTTP request to `app.example.com`.
2. The request arrives at the Vacuum Wall host's WAN interface, assigned to the `external` firewalld zone. A firewall rule allows inbound traffic on port 443 (HTTPS).
3. nginx, listening on port 443, terminates the TLS connection using the domain's certificate.
4. nginx evaluates the `server_name` against the configured server blocks. The matching block is generated from the domain entry in `config/nginx/config.json`.
5. The request is forwarded to the backend service (e.g., `192.168.2.50:8080`) via an `proxy_pass` directive.
6. The backend service processes the request and returns an HTTP response.
7. nginx adds security headers (`X-Content-Type-Options`, `X-Frame-Options`, HSTS, etc.) to the response.
8. nginx encrypts the response with TLS and sends it back to the client through the WAN interface.

For HTTP requests (port 80), nginx returns a 301 redirect to the HTTPS equivalent before any proxying occurs.

### Management WebUI Access (e.g., `<hostname>.local`)

1. A client sends an HTTPS request to the management domain.
2. nginx terminates TLS and checks for HTTP Basic Authentication credentials against the `.htpasswd` file.
3. If authentication succeeds, the request is proxied to `127.0.0.1:9090` where the Flask WebUI is listening.
4. The Flask application processes the request and communicates with the `vacuum-walld` daemon via a Unix socket (`data/daemon.sock`) for any privileged operations.
5. The daemon executes the privileged commands via the sudo whitelist and returns structured results.
6. Flask renders an HTML or JSON response, which nginx returns to the client over the encrypted connection.

Because Flask binds only to `127.0.0.1`, it is unreachable directly from any external interface. The nginx reverse proxy is the sole entry point.

## Subsystem Communication

The following diagram summarizes how the Flask WebUI communicates with each managed subsystem:

```
External Client ──→ nginx (SSL termination) ──→ Flask WebUI (127.0.0.1:9090)
Flask WebUI ──→ daemon/client.py (path resolution, Unix socket) ──→ vacuum-walld (aiohttp server)
vacuum-walld ──→ daemon/handlers/firewall.py ──→ sudo firewall-cmd ──→ firewalld / D-Bus ──→ nftables
vacuum-walld ──→ daemon/handlers/nginx.py ──→ write local .conf files ──→ sudo cp to /etc/nginx/ ──→ sudo nginx -t && sudo nginx -s reload
vacuum-walld ──→ daemon/handlers/dnsmasq.py ──→ render config ──→ sudo tee /etc/dnsmasq.d/vacuum-wall.conf ──→ sudo systemctl reload dnsmasq
vacuum-walld ──→ daemon/handlers/acme.py ──→ acme.sh (subprocess) ──→ deploy hook (daemon API) ──→ ACME provider
vacuum-walld ──→ daemon/handlers/wireguard.py ──→ render data/wireguard/wg0.conf ──→ sudo cp to /etc/wireguard/ ──→ sudo wg-quick up wg0
vacuum-walld ──→ daemon/handlers/network.py ──→ render 50-<name>.network ──→ sudo cp to /etc/systemd/network/ ──→ sudo networkctl reload
vacuum-walld ──→ daemon/handlers/logs.py ──→ sudo journalctl ──→ systemd journal
```

### Two-User Model with Shared Group

Vacuum Wall uses two distinct system users bridged by a shared group:

- **`vacuum-walld`** (daemon user): Runs the privileged background daemon. Holds the NOPASSWD sudo whitelist for all system-level commands. Runs with `NoNewPrivileges=yes` (satisfiable since sudo is called directly by the daemon process).
- **WebUI user** (default: repo owner in `--dev` mode): Runs the Flask web serving process. Has **zero** sudo access. Communicates with the daemon via a Unix socket at `data/daemon.sock`. Runs with `NoNewPrivileges=yes`.
- **Shared group**: Both users share the WebUI user's primary group. The daemon socket is owned by `vacuum-walld:<group>` with mode `0660`, allowing the web UI user to connect via group permission. The project directory is owned by the WebUI user with group-read+execute, giving the daemon read access to configs and shared files.

This design isolates privilege escalation entirely within the daemon, so a compromised Flask process cannot invoke sudo directly. The `lib/` modules no longer contain sudo calls; all privileged command execution lives in `daemon/handlers/*.py`.

**Dev mode variant**: When `install.sh --dev` is used, the repo owner (e.g., `wall`) becomes the WebUI user. The project directory remains owned by the repo owner, preserving git operations and code editing. The daemon user (`vacuum-walld`) has the repo owner's primary group as its own primary group, granting read access to project files. All subdirectories carry the setgid bit (`g+s`) so new files inherit the group regardless of the creator's primary group.

The `lib/` modules auto-discover the project root at runtime via `Path(__file__).resolve().parent.parent`. This works because `install.sh` performs an editable pip install (`pip install -e .`), keeping module files in the project directory rather than copying them to `site-packages/`.

## Install-Time Templating

System configuration files in `system/` are Jinja2 templates rendered by `install.sh` at install time:

- **`systemd/vacuum-wall.service`**, **`systemd/vacuum-walld.service`**, **`systemd/vacuum-wall-acme.service`** — `{{ USER_NAME }}`, `{{ USER_DAEMON_NAME }}`, `{{ USER_GROUP }}`, `{{ PROJECT_DIR }}`, `{{ ACME_HOME }}` are substituted to produce the final systemd unit files installed to `/etc/systemd/system/`. The `PROJECT_DIR` template variable is set from the `INSTALL_DIR` environment variable (defaults to the repo root).
- **`sudoers.d/vacuum-walld`** — `{{ USER_DAEMON_NAME }}` is substituted to produce the sudoers whitelist for the daemon user.
- The timer file (`vacuum-wall-acme.timer`) contains no variable paths and is installed as-is.

Runtime templates (`system/nginx/*.conf`, `system/dnsmasq.conf`, `system/wireguard*.conf`) are rendered at runtime by `lib/` modules via Jinja2 with Python data.

## State Management

Vacuum Wall uses a declarative configuration model. Persistent user-facing configuration lives in `config/<subsystem>/config.json`. Runtime artifacts and generated files live in `data/<subsystem>/`. The application renders these declarations into the format expected by the underlying system service.

| Subsystem | Declarative Config | Runtime Data | Rendered Target | State Persistence |
|---|---|---|---|---|
| firewalld | `config/firewall/config.json` | `data/firewall/rules.json` | N/A (commands issued directly to firewalld via D-Bus) | firewalld manages its own persistent state in `/etc/firewalld/`. `config.json` is the declarative source of truth. `rules.json` serves as an automated backup snapshot. |
| dnsmasq | `config/dnsmasq/config.json` | `data/dnsmasq/fragments/` | `/etc/dnsmasq.d/vacuum-wall.conf` | The JSON file is the source of truth. The rendered `.conf` file is overwritten on each apply. |
| nginx | `config/nginx/config.json` | `data/nginx/.htpasswd`, `data/nginx/sites-enabled/` | `data/nginx/sites-enabled/<domain>.conf` + `/etc/nginx/conf.d/vacuum-wall.conf` | All proxy and management domain definitions are derived from the JSON config. Generated `.conf` files are overwritten on each apply. |
| WireGuard | `config/wireguard/config.json` | `data/wireguard/` | `/etc/wireguard/wg0.conf` | The JSON file defines the interface and all peers. The rendered WireGuard config is overwritten on each apply. |
| networkd | `config/network/config.json` | `data/networkd/` | `/etc/systemd/network/50-<name>.network` | The JSON file defines per-interface static addresses, routes, DNS, DHCP, and link settings. Each entry renders to a `50-<name>.network` INI file. Stale files are cleaned on apply. Public DNS servers are auto-synced to dnsmasq upstreams. |
| ACME | `config/acme/config.json` | `data/acme/` | Certificate and key files | acme.sh manages its own state, renewal scheduling, and account keys. Vacuum Wall triggers issuance and renewal but does not maintain independent ACME state. Account registration (email, CA provider) is stored in the declarative config. |

#### Background Polling

The daemon runs background polling tasks for subsystems with external runtime state. Each subsystem has a configurable interval and a two-layer diff (structural vs volatile) to minimize unnecessary broadcasts.

| Subsystem | Interval | Rationale |
|-----------|----------|-----------|
| firewall | 30s | Most expensive collector (6+ subprocess calls) |
| wireguard | 10s | Peer connections/handshakes change frequently |
| dnsmasq | 10s | Lease file + service status |
| networkd | 10s | Interface up/down, DHCP address changes |

nginx and acme are not polled — they have no external runtime state.

**Two-layer diff:** Each poll cycle classifies changes as:
- **Structural change** (zones added, peers removed, config changed): triggers `bump()` + broadcast `{"type": "versions", ...}` → full UI re-load
- **Volatile change only** (transfer counters, DHCP-assigned IPs): sends `{"type": "tick", "subsystems": [...]}` → lightweight per-subsystem re-fetch
- **No change**: silence

Volatile fields per subsystem: `wireguard` (peer transfer/handshake stats), `firewall` (DHCP-assigned IPs), `networkd` (DHCP addresses, link metrics). Defined per collector via `register_volatile()`.

Poll intervals are configurable via `VACUUM_WALL_POLL_INTERVALS` env var (`firewall:30,wireguard:10,...`).

On collector failure during a poll, no broadcast is sent (avoids noisy ticks). State data is set to `None`.

## Cross-Subsystem Sync Event Bus

When a subsystem's configuration changes, related subsystems are automatically
updated to stay consistent. An in-process event bus (`lib/sync.py`) decouples
subsystems — no handler calls into another handler's logic directly.

### How It Works

1. A mutation handler saves its config (e.g., adding a DHCP range).
2. The handler emits a `SyncEvent` on the event bus.
3. Subscribers react by updating related subsystem configs:
   - **DnsToFirewallSync**: Adds `dhcp`, `dns` services and `masquerade` to the
     firewall zone for each interface serving a DHCP range.
   - **WgToFirewallSync**: Creates or updates a `vpn` firewall zone with
     WireGuard interface and UDP 51820 rich rule.
   - **FirewallToDhcpSync**: Detects stale DHCP ranges for interfaces not in
     any zone (logs warnings, does not auto-remove).
   - **NetworkToAllSync**: Suggests DHCP ranges and syncs firewall zone
     interface assignments when network config changes.
4. The handler refreshes state for the originating subsystem plus all
   transitively affected subsystems.

### Guard Rails

- **Idempotency**: Each subscriber reads current state, computes desired state,
  writes the diff. Running twice is safe.
- **No loops**: The event bus tracks `(subsystem, action)` per dispatch cycle.
  Re-entrant emits for the same key are silently dropped.
- **Firewall-cmd separation**: Sync subscribers only write JSON config. They
  do NOT call `firewall-cmd`. The user clicks "Apply" on the firewall page to
  push to firewalld.
- **Error handling**: Subscriber exceptions are caught, logged as warnings,
  and do NOT abort the originating handler.

### Frontend Impact

Minimal. The sync happens transparently in the backend. The "pending changes"
indicator on the firewall page will show pending when DHCP or WireGuard saves
(since sync writes JSON but does not call firewall-cmd).

## Directory Structure

### Config — Declarative Settings

Config files are persistent, user-editable JSON that defines the desired state for each subsystem:

```
config/
├── dnsmasq/
│   └── config.json                   # DHCP ranges, static leases, DNS forwarding, custom records
├── firewall/
│   └── config.json                   # Firewall zones, rich rules, forward ports
├── nginx/
│   └── config.json                   # Proxy domain definitions, management domain, SSL settings
└── wireguard/
    └── config.json                   # WireGuard interface and peer configuration
├── network/
│   └── config.json                   # Per-interface static IP, routes, DNS, DHCP settings
```

### Data — Runtime Artifacts

The `data/` directory holds generated files, credentials, and subsystem artifacts:

```
data/
├── nginx/
│   ├── .htpasswd                     # HTTP Basic Authentication credentials for management UI
│   └── sites-enabled/                # Generated nginx server block .conf files (one per domain)
├── dnsmasq/
│   └── fragments/                    # User-defined dnsmasq config fragments (appended verbatim)
├── firewall/
│   └── rules.json                    # Auto-generated firewall rule state backup
├── acme/                             # ACME certificate files (acme.sh home)
├── logs/
│   └── vacuum-wall.log              # Application log file
└── wireguard/                        # WireGuard runtime artifacts
├── networkd/                         # Generated 50-<name>.network files
```

Both `config/` and `data/` reside within the project directory. The systemd service unit's `ReadWritePaths` directive grants the Flask process write access to both directories, while keeping the rest of the filesystem read-only. The `INSTALL_DIR` value is templated into the service unit at install time.

## File System Layout

The following file system locations are used for integration with system services:

| Path | Purpose | Managed By |
|---|---|---|
| `/etc/nginx/conf.d/vacuum-wall.conf` | Include directive that pulls in `data/nginx/sites-enabled/*.conf`. | Vacuum Wall (lib/nginx.py) |
| `/etc/nginx/snippets/vacuum-wall-ssl.conf` | Shared SSL configuration snippet (protocols, ciphers, DH parameters, OCSP). Included by all HTTPS server blocks. | Vacuum Wall (lib/nginx.py) |
| `/etc/dnsmasq.d/vacuum-wall.conf` | Generated dnsmasq configuration file. Written from `config/dnsmasq/config.json`. | Vacuum Wall (lib/dnsmasq.py) |
| `/etc/wireguard/wg0.conf` | Generated WireGuard interface configuration. Written from `config/wireguard/config.json`. | Vacuum Wall (lib/wireguard.py) |
| `/etc/systemd/network/50-<name>.network` | Generated systemd-networkd drop-in files. Written from `config/network/config.json`, one per interface. | Vacuum Wall (lib/network.py) |
| `/etc/sudoers.d/vacuum-walld` | Sudo whitelist for the daemon user. Defines all permitted privilege escalations. | Install script (rendered from Jinja2 template) |

The `/etc/nginx/conf.d/vacuum-wall.conf` include file ensures that all domain-specific configurations in `sites-enabled/` are loaded by nginx without modifying the main `nginx.conf`. The SSL snippet keeps TLS settings consistent across all managed domains and allows global updates from a single location.

## Frontend Architecture

The web UI is a single-page application built on **Hoover**, a custom lightweight VDOM framework. See [Hoover Framework Reference](hoover.md) for the complete API.

### Request Flow (Frontend)

```
Client requests / ──→ nginx ──→ Flask (server-side __WS_URL_PLACEHOLDER__ substitution)
Client loads /static/app.js ──→ Hoover initializes, mounts #sidebar and #main render roots
Hoover connects WebSocket ──→ daemon/ws (127.0.0.1:9091)
Page navigate (hash change) ──→ reactive router state updates ──→ render engine re-executes ──→ VDOM diff patches DOM
User action (form submit) ──→ apiFetch() ──→ Flask REST API ──→ daemon/client.py ──→ vacuum-walld
WebSocket message (versions) ──→ topic match ──→ page load() re-executed ──→ state updated ──→ render engine patches DOM
```

The SPA entry point only serves `index.html` at `/`. All other paths return 404. Non-API, non-static paths are not served by Flask — the client-side router handles all navigation via hash changes. A dedicated `/vendor/<path>` route serves vendored JS libraries.

### Component Model

Each route is a `definePage()` component with reactive state, async data loading, and WebSocket auto-refresh. Pages are mounted using `hComp(page, key)` in the router, where the key determines lifecycle boundaries. The same key reuses the component instance (preserving state); a different key unmounts the old page and mounts the new one.

### No Build Step

All JavaScript is served as ES modules. The `?v=N` query string param version-pins asset imports for cache invalidation. Dev mode (`VACUUM_WALL_DEV`) disables aggressive static asset caching.

### WebSocket Broadcast

The daemon broadcasts state-change notifications via WebSocket. Hoover's `subscribe` mechanism maps page-level topic subscriptions to automatic `load()` re-executions. Messages are debounced (300ms) and in-flight loads are aborted before re-loading, ensuring the UI always displays the latest available data.

## Zone Model

The firewalld zone layout in Vacuum Wall follows a defense-in-depth approach, segmenting traffic based on trust level:

| Zone | Interfaces | Trust Level | Description |
|---|---|---|---|
| `public` / `external` | WAN (e.g., `eth0`) | Untrusted | Internet-facing. Only explicitly allowed inbound services (HTTPS/443, WireGuard/51820, ICMP echo rate-limited) are accessible. All other inbound traffic is dropped. |
| `internal` | LAN (e.g., `eth1`) | Trusted | Local area network. DHCP (UDP 67/68) and DNS (UDP/TCP 53) are served. Masquerade (NAT) is enabled for outbound Internet access from LAN clients. Inbound from WAN to this zone is not directly accessible. |
| `vpn` | WireGuard (`wg0`) | Semi-trusted | WireGuard tunnel interface. Firewall rules determine which internal services and subnets VPN peers can reach. By default, VPN peers can access the Internet but may be restricted from accessing management interfaces or sensitive LAN services. |
| `trusted` | Management interface | Administrative | Used for management traffic. The `loopback` zone covers localhost communication, enabling the Flask WebUI to receive proxied requests from nginx on `127.0.0.1:9090`. |

### Custom Zones

Additional zones can be created for specialized network segments:

- **DMZ zone**: For hosting public-facing services that need to be isolated from the internal LAN. Traffic from the DMZ to the `internal` zone is denied by default.
- **Guest zone**: For visitor Wi-Fi or untrusted devices. Access is limited to outbound Internet traffic only, with no access to `internal` or `vpn` zones.
- **IoT zone**: For devices requiring restricted outbound access (e.g., blocking telemetry domains).

Each custom zone can define its own source rules, port forwardings, and inter-zone traffic policies. The Flask WebUI provides interfaces to create, modify, and assign interfaces to zones at runtime.