Add lite mode: optional Redis and Celery dependencies

- Session backend falls back to SQLAlchemy when Redis unavailable
- Celery only initializes when installed and configured
- Move redis/celery to [full] optional dependencies
- Zero-config startup with uv sync && flask run

Author: level09

enferno/app.py

@@ -61,7 +61,9 @@ def clear_workspace_on_login(sender, user, **extra):
     if debug_toolbar:
         debug_toolbar.init_app(app)
 
-    # Session initialization
+    # Session initialization - pass db for SQLAlchemy sessions
+    if app.config.get("SESSION_TYPE") == "sqlalchemy":
+        app.config["SESSION_SQLALCHEMY"] = db
     session.init_app(app)
 
     babel.init_app(

enferno/settings.py

@@ -1,13 +1,27 @@
+import importlib.util
 import os
 from datetime import timedelta
 
 import bleach
-import redis
 from dotenv import load_dotenv
 
+# Detect optional dependencies (installed via --extra full)
+REDIS_AVAILABLE = importlib.util.find_spec("redis") is not None
+
 os_env = os.environ
 load_dotenv()
 
+# Session configuration - computed at module level
+_redis_url = os.environ.get("REDIS_URL") or os.environ.get("REDIS_SESSION")
+if REDIS_AVAILABLE and _redis_url:
+    import redis  # type: ignore[import-not-found]
+
+    _SESSION_TYPE = "redis"
+    _SESSION_REDIS = redis.from_url(_redis_url)
+else:
+    _SESSION_TYPE = "sqlalchemy"
+    _SESSION_REDIS = None
+
 
 def uia_username_mapper(identity):
     # Sanitize and strip whitespace from email input - Flask-Security handles case insensitivity
@@ -28,9 +42,10 @@ class Config:
     # SQLALCHEMY_DATABASE_URI = os.environ.get('SQLALCHEMY_DATABASE_URI', 'postgresql:///enferno')
     SQLALCHEMY_TRACK_MODIFICATIONS = True
 
-    CELERY_BROKER_URL = os.environ.get("CELERY_BROKER_URL", "redis://localhost:6379/2")
-    CELERY_RESULT_BACKEND = os.environ.get(
-        "CELERY_RESULT_BACKEND", "redis://localhost:6379/3"
+    # Celery configuration - only set if Redis available and configured
+    CELERY_BROKER_URL = os.environ.get("CELERY_BROKER_URL") if REDIS_AVAILABLE else None
+    CELERY_RESULT_BACKEND = (
+        os.environ.get("CELERY_RESULT_BACKEND") if REDIS_AVAILABLE else None
     )
 
     # security
@@ -83,11 +98,10 @@ class Config:
 
     SESSION_PROTECTION = "strong"
 
-    # Session configuration
-    SESSION_TYPE = "redis"
-    SESSION_REDIS = redis.from_url(
-        os.environ.get("REDIS_SESSION", "redis://localhost:6379/1")
-    )
+    # Session configuration - uses module-level computed values
+    SESSION_TYPE = _SESSION_TYPE
+    SESSION_REDIS = _SESSION_REDIS
+    SESSION_SQLALCHEMY_TABLE = "sessions"
     SESSION_KEY_PREFIX = "session:"
     SESSION_USE_SIGNER = True
     PERMANENT_SESSION_LIFETIME = 3600

enferno/tasks/__init__.py

@@ -1,30 +1,37 @@
-from celery import Celery
+import importlib.util
 
-from enferno.settings import Config as cfg
+# Detect optional dependencies
+CELERY_AVAILABLE = importlib.util.find_spec("celery") is not None
 
-celery = Celery(
-    "enferno.tasks",
-    broker=cfg.CELERY_BROKER_URL,
-    backend=cfg.CELERY_RESULT_BACKEND,
-    broker_connection_retry_on_startup=True,
-)
+celery = None
 
-celery.conf.add_defaults(cfg)
+if CELERY_AVAILABLE:
+    from celery import Celery  # type: ignore[import-not-found]
 
+    from enferno.settings import Config as cfg
 
-class ContextTask(celery.Task):
-    abstract = True
+    # Only initialize Celery if broker is configured
+    if cfg.CELERY_BROKER_URL:
+        celery = Celery(
+            "enferno.tasks",
+            broker=cfg.CELERY_BROKER_URL,
+            backend=cfg.CELERY_RESULT_BACKEND,
+            broker_connection_retry_on_startup=True,
+        )
 
-    def __call__(self, *args, **kwargs):
-        from enferno.app import create_app
+        celery.conf.add_defaults(cfg)
 
-        with create_app(cfg).app_context():
-            return super().__call__(*args, **kwargs)
+        class ContextTask(celery.Task):
+            abstract = True
 
+            def __call__(self, *args, **kwargs):
+                from enferno.app import create_app
 
-celery.Task = ContextTask
+                with create_app(cfg).app_context():
+                    return super().__call__(*args, **kwargs)
 
+        celery.Task = ContextTask
 
-@celery.task
-def task():
-    pass
+        @celery.task
+        def task():
+            pass

pyproject.toml

@@ -39,12 +39,6 @@ dependencies = [
     "webauthn>=2.6.0",
     "cffi>=1.17.1",
     "pycparser>=2.22",
-    # Task queue and caching
-    "celery>=5.5.3",
-    "redis>=6.2.0",
-    "amqp>=5.3.1",
-    "kombu>=5.5.4",
-    "vine>=5.1.0",
     # Utilities and data handling
     "email-validator>=2.2.0",
     "python-dotenv>=1.1.1",
@@ -72,6 +66,13 @@ dependencies = [
 ]
 
 [project.optional-dependencies]
+full = [
+    "redis>=7.1.0",
+    "celery>=5.5.3",
+    "kombu>=5.5.4",
+    "amqp>=5.3.1",
+    "vine>=5.1.0",
+]
 dev = [
     # Code formatting and linting
     "ruff",