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10) Implement explicit startup DAG for resource initialization

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- Created StartupDAG class to orchestrate startup stages with explicit dependencies
- Defined 6 startup stages: WORKER_MODE → DATABASE → GEO_CACHE → HTTP_SESSION → SCHEDULER → TASKS
- Each stage has prerequisites, error handling, and rollback support
- Refactored startup_shared_resources() to use the DAG
- Added StartupContext for resource tracking and failure management
- Partial failures automatically roll back all completed resources in reverse order
- Added health checks to verify all resources initialized successfully
- Comprehensive test coverage: 15 DAG unit tests + 3 integration tests + 6 existing tests
- Documented startup DAG in Architekture.md with detailed stage descriptions and failure modes

This replaces implicit ordering with explicit dependency tracking, making lifecycle
changes safe and failure modes predictable. Hidden order dependencies no longer exist.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
This commit is contained in:
Lukas
2026-04-28 08:08:05 +02:00
parent a273b96563
commit e86ab6dad1
6 changed files with 1128 additions and 79 deletions
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273
backend/app/startup.py
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@@ -3,14 +3,27 @@
This module contains shared startup logic extracted from ``app.main`` so that
initialisation is easier to reason about and unit test. The lifespan handler
in ``app.main`` delegates resource creation and task registration here.
The startup process is orchestrated by StartupDAG, which ensures all resources
are initialized in the correct order with explicit dependency tracking, and
cleanly rolls back on failure.
Startup Stages (in order):
1. WORKER_MODE: Verify single-worker mode (no multi-worker scheduler conflicts)
2. DATABASE: Initialize database schema and cache setup completion state
3. GEO_CACHE: Load and configure IP geolocation cache
4. HTTP_SESSION: Create shared aiohttp session with timeouts
5. SCHEDULER: Create APScheduler instance and register background tasks
6. TASKS: Verify all tasks are registered
See StartupDAG in app.startup_dag for full dependency graph and rollback logic.
"""
from __future__ import annotations
import os
from contextlib import suppress
from pathlib import Path
from typing import TYPE_CHECKING
from typing import TYPE_CHECKING, Any
import aiohttp
import structlog
@@ -19,6 +32,7 @@ from apscheduler.schedulers.asyncio import AsyncIOScheduler # type: ignore[impo
from app.db import init_db, open_db
from app.services import setup_service
from app.services.geo_cache import GeoCache
from app.startup_dag import StartupDAG, StartupStage
from app.tasks import (
blocklist_import,
geo_cache_cleanup,
@@ -105,15 +119,146 @@ async def startup_shared_resources(
) -> tuple[aiohttp.ClientSession, AsyncIOScheduler]:
"""Create shared resources needed during the application lifespan.
This function orchestrates the entire startup sequence through a StartupDAG,
ensuring all resources are initialized in the correct order with explicit
dependency tracking. If any stage fails, all completed resources are cleanly
rolled back.
The startup stages are:
1. WORKER_MODE: Validate single-worker configuration
2. DATABASE: Initialize database and load setup state
3. GEO_CACHE: Load IP geolocation cache
4. HTTP_SESSION: Create shared aiohttp session
5. SCHEDULER: Create and start APScheduler
6. TASKS: Register all background jobs
Args:
app: The FastAPI application instance.
settings: Resolved application settings.
Returns:
A tuple of ``(http_session, scheduler)``.
Raises:
RuntimeError: If any startup stage fails or prerequisites are not met.
"""
dag = StartupDAG()
# Register all startup stages with their dependencies.
dag.register_stage(
StartupStage.WORKER_MODE,
"Verify single-worker mode (scheduler must not run in multiple workers)",
prerequisites=frozenset(),
)
dag.register_stage(
StartupStage.DATABASE,
"Initialize database schema and load setup state",
prerequisites=frozenset([StartupStage.WORKER_MODE]),
)
dag.register_stage(
StartupStage.GEO_CACHE,
"Load IP geolocation cache from database",
prerequisites=frozenset([StartupStage.DATABASE]),
)
dag.register_stage(
StartupStage.HTTP_SESSION,
"Create shared aiohttp session with configured timeouts",
prerequisites=frozenset([StartupStage.GEO_CACHE]),
)
dag.register_stage(
StartupStage.SCHEDULER,
"Create and start APScheduler for background jobs",
prerequisites=frozenset([StartupStage.HTTP_SESSION]),
)
dag.register_stage(
StartupStage.TASKS,
"Register all background jobs (import, cleanup, health checks)",
prerequisites=frozenset([StartupStage.SCHEDULER]),
)
try:
# Stage 1: Validate single-worker mode
await dag.execute_stage(
StartupStage.WORKER_MODE,
_stage_check_worker_mode,
)
# Stage 2: Initialize database
startup_db = await dag.execute_stage(
StartupStage.DATABASE,
lambda: _stage_init_database(app, settings),
)
# Stage 3: Load GeoCache
geo_cache = await dag.execute_stage(
StartupStage.GEO_CACHE,
lambda: _stage_init_geo_cache(settings, startup_db),
)
# Stage 4: Create HTTP session
http_session = await dag.execute_stage(
StartupStage.HTTP_SESSION,
lambda: _stage_create_http_session(settings),
)
# Stage 5: Create and start scheduler
scheduler = await dag.execute_stage(
StartupStage.SCHEDULER,
lambda: _stage_create_scheduler(),
)
# Stage 6: Register tasks
await dag.execute_stage(
StartupStage.TASKS,
lambda: _stage_register_tasks(app, scheduler),
)
# Verify all resources are healthy
if not await dag.health_check():
raise RuntimeError("Startup health check failed")
# Store the geo_cache on app state for dependency injection
app.state.geo_cache = geo_cache
log.info(
"startup_completed_successfully",
stages=len(dag.context.completed_stages),
)
return http_session, scheduler
except Exception:
# Clean up on failure
log.error("startup_failed_rolling_back_resources")
await dag.rollback()
# Ensure database is closed if it was initialized
if StartupStage.DATABASE in dag.context.completed_stages:
startup_db = dag.context.get_resource(StartupStage.DATABASE)
await startup_db.close()
raise
async def _stage_check_worker_mode() -> None:
"""Check that the application is running with a single worker.
This is stage 1 of the startup DAG.
"""
_check_single_worker_mode()
async def _stage_init_database(app: FastAPI, settings: Settings) -> Any:
"""Initialize database schema and load setup state.
This is stage 2 of the startup DAG. It:
1. Creates database directory if needed
2. Opens the database connection
3. Initializes schema
4. Caches setup completion state
5. Loads persisted runtime settings
Returns:
The database connection object.
"""
db_path: Path = Path(settings.database_path)
await run_blocking(db_path.parent.mkdir, parents=True, exist_ok=True)
@@ -121,6 +266,7 @@ async def startup_shared_resources(
original_db_path = db_path.resolve()
startup_db = await open_db(settings.database_path)
try:
await init_db(startup_db)
setup_complete = await setup_service.is_setup_complete(startup_db)
@@ -144,36 +290,53 @@ async def startup_shared_resources(
if persisted_runtime_settings:
updated_settings = settings.model_copy(update=persisted_runtime_settings)
set_runtime_settings(app, updated_settings)
settings = updated_settings
log.info(
"runtime_settings_overridden_from_setup",
overrides=persisted_runtime_settings,
)
# Create and initialize the GeoCache instance
geo_cache = GeoCache(allow_http_fallback=settings.geoip_allow_http_fallback)
if Path(settings.database_path).resolve() != original_db_path:
runtime_db = await open_db(settings.database_path)
try:
await geo_cache.load_cache_from_db(runtime_db)
unresolved_count = await geo_cache.count_unresolved(runtime_db)
finally:
await runtime_db.close()
else:
await geo_cache.load_cache_from_db(startup_db)
unresolved_count = await geo_cache.count_unresolved(startup_db)
finally:
except Exception:
await startup_db.close()
raise
return startup_db
async def _stage_init_geo_cache(settings: Settings, startup_db: Any) -> GeoCache:
"""Load IP geolocation cache.
This is stage 3 of the startup DAG. It:
1. Creates GeoCache instance with configured settings
2. Loads cache from database
3. Counts unresolved IPs
4. Initializes GeoIP database
5. Logs warnings if necessary
Returns:
The GeoCache instance.
"""
geo_cache = GeoCache(allow_http_fallback=settings.geoip_allow_http_fallback)
db_path: Path = Path(settings.database_path)
original_db_path = db_path.resolve()
if db_path.resolve() != original_db_path:
runtime_db = await open_db(settings.database_path)
try:
await geo_cache.load_cache_from_db(runtime_db)
unresolved_count = await geo_cache.count_unresolved(runtime_db)
finally:
await runtime_db.close()
else:
await geo_cache.load_cache_from_db(startup_db)
unresolved_count = await geo_cache.count_unresolved(startup_db)
await run_blocking(ensure_jail_configs, Path(settings.fail2ban_config_dir) / "jail.d")
if unresolved_count > 0:
log.warning("geo_cache_unresolved_ips", unresolved=unresolved_count)
http_session: aiohttp.ClientSession = _create_http_session(settings)
geo_cache.init_geoip(settings.geoip_db_path)
# Warn if HTTP fallback is enabled (security warning).
if settings.geoip_allow_http_fallback:
log.warning(
"geoip_http_fallback_enabled",
@@ -184,26 +347,58 @@ async def startup_shared_resources(
),
)
app.state.geo_cache = geo_cache
return geo_cache
scheduler: AsyncIOScheduler | None = None
try:
scheduler = AsyncIOScheduler(timezone="UTC")
scheduler.start()
health_check.register(app)
await blocklist_import.register(app)
geo_cache_cleanup.register(app)
geo_cache_flush.register(app)
geo_re_resolve.register(app)
history_sync.register(app)
session_cleanup.register(app)
async def _stage_create_http_session(settings: Settings) -> aiohttp.ClientSession:
"""Create shared aiohttp session with configured timeouts.
return http_session, scheduler
except Exception:
with suppress(Exception):
await http_session.close()
if scheduler is not None:
with suppress(Exception):
scheduler.shutdown(wait=False)
raise
This is stage 4 of the startup DAG.
Returns:
The aiohttp ClientSession instance.
"""
return _create_http_session(settings)
async def _stage_create_scheduler() -> AsyncIOScheduler:
"""Create and start APScheduler.
This is stage 5 of the startup DAG.
Returns:
The AsyncIOScheduler instance.
Raises:
RuntimeError: If scheduler creation or startup fails.
"""
scheduler: AsyncIOScheduler = AsyncIOScheduler(timezone="UTC")
scheduler.start()
return scheduler
async def _stage_register_tasks(app: FastAPI, scheduler: AsyncIOScheduler) -> None:
"""Register all background jobs.
This is stage 6 of the startup DAG. It registers:
- health_check: Periodic fail2ban connectivity probe
- blocklist_import: Scheduled blocklist download and application
- geo_cache_cleanup: Periodic purge of stale geo cache entries
- geo_cache_flush: Periodic geo cache persistence
- geo_re_resolve: Periodic re-resolution of stale records
- history_sync: Periodic synchronization of ban history
- session_cleanup: Periodic cleanup of expired sessions
Args:
app: The FastAPI application instance.
scheduler: The APScheduler scheduler to register tasks with.
"""
health_check.register(app)
await blocklist_import.register(app)
geo_cache_cleanup.register(app)
geo_cache_flush.register(app)
geo_re_resolve.register(app)
history_sync.register(app)
session_cleanup.register(app)
log.info("startup_tasks_registered", count=7)