FabledSteward/docs/architecture.md

Architecture

Fabled Scryer is a single Quart (async Python) process. There are no separate worker processes, no message brokers, and no build pipeline for the frontend. All monitoring, scheduling, and request handling runs on a single asyncio event loop.

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Startup Sequence

create_app() in fabledscryer/app.py runs these steps synchronously before the event loop starts:

Step	What happens
1	Bootstrap config loaded (database_url, secret_key, plugin_dir)
2	SQLAlchemy async engine and session factory attached to app
3	Core Alembic migrations applied (creates app_settings table among others)
4	All settings loaded from app_settings DB table into app.config
5	Each enabled plugin's Alembic migrations applied
6	Alert pipeline initialised (init_alerts(app) stores app ref for deferred notifications)
7	Core blueprints registered (auth, dashboard, hosts, ping, dns, alerts, ansible, settings)
8	Core scheduled tasks registered into app._task_registry
9	Plugins loaded via load_plugins(app) — blueprints and tasks appended
10	/health endpoint registered
11	before_serving hook starts the scheduler as an asyncio.create_task()

The two-phase migration approach (step 3 core → step 4 load settings → step 5 plugins) exists because plugin enabling is stored in the settings DB, which requires the core schema to exist first.

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Request Routing

All routes are Quart Blueprints registered in app.py:

Prefix	Blueprint	Module
/auth/	auth_bp	fabledscryer/auth/routes.py
/	dashboard_bp	fabledscryer/dashboard/routes.py
/hosts/	hosts_bp	fabledscryer/hosts/routes.py
/ping/	ping_bp	fabledscryer/ping/routes.py
/dns/	dns_bp	fabledscryer/dns/routes.py
/alerts/	alerts_bp	fabledscryer/alerts/routes.py
/ansible/	ansible_bp	fabledscryer/ansible/routes.py
/settings/	settings_bp	fabledscryer/settings/routes.py
/plugins/<name>/	plugin blueprint	plugins/<name>/routes.py

Plugin blueprints are mounted automatically by load_plugins() using the plugin directory name as the URL prefix.

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Scheduler

fabledscryer/core/scheduler.py exports two things:

• ScheduledTask dataclass — holds a name, coro_factory (zero-argument callable returning a coroutine), interval_seconds, and optional run_on_startup flag
• start_scheduler(tasks) — async function that loops every second, calling asyncio.create_task() for each task whose interval has elapsed

Tasks are never awaited serially — each runs as a fully independent asyncio task. Exceptions inside tasks are caught and logged; they do not crash other tasks or the app.

Core tasks registered in app._task_registry:

• ping_monitor — runs every monitors.poll_interval_seconds (default 60s), run_on_startup=True
• dns_monitor — same interval, run_on_startup=True
• data_cleanup — runs hourly, run_on_startup=False
• ansible_git_pull_<name> — one per configured Git source, interval from source config

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Database Session Pattern

app.db_sessionmaker is an SQLAlchemy async_sessionmaker. All DB access follows this pattern:

async with current_app.db_sessionmaker() as session:
    async with session.begin():
        # queries and writes here
        # transaction commits on exit, rolls back on exception

Sessions are never shared across request boundaries or between tasks.

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Config Two-Layer Design

There are exactly two config layers:

1. Bootstrap (config.yaml + env vars) — database_url, secret_key, plugin_dir only. Read once at startup before the event loop.
2. App settings (app_settings DB table) — everything else: SMTP, webhooks, Ansible sources, monitor intervals, ping thresholds, plugin config. Read at startup via load_settings_sync() and written via the Settings UI at runtime.

This means the only file you must touch to get the app running is the database URL. Everything else can be configured through the web UI.

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Frontend Approach

No JavaScript framework, no build step. The frontend is:

• Jinja2 templates rendered server-side (fabledscryer/templates/)
• HTMX for live-updating fragments (dashboard widgets, ping pills, DNS status)
• A single CSS design system in fabledscryer/templates/base.html using CSS custom properties

Live-updating widgets use HTMX polling:

<div hx-get="/ping/rows" hx-trigger="load, every 30s" hx-swap="innerHTML">

Fragment endpoints (/ping/rows, /dns/rows, /plugins/traefik/widget) return partial HTML that HTMX swaps in without a full page reload.