adhocracy-plus/config: adds support for celery task queues

adhocracy-plus/config/celery.py

@@ -0,0 +1,23 @@
+import os
+
+from celery import Celery
+
+os.environ.setdefault("DJANGO_SETTINGS_MODULE", "adhocracy-plus.config.settings")
+
+
+class Config:
+    broker_url = "redis://localhost:6379"
+    result_backend = "redis"
+    broker_connection_retry_on_startup = True
+
+
+celery = Celery(main="adhocracy-plus")
+celery.config_from_object(Config)
+celery.autodiscover_tasks()
+
+
+@celery.task
+def celery_dummy_task():
+    print("hello")
+
+    return "world"

adhocracy-plus/config/settings/base.py

@@ -111,6 +111,8 @@
     "apps.polls",
     "apps.topicprio",
     "apps.debate",
+    # Celery
+    "celery",
 )
 
 MIDDLEWARE = (

apps/__init__.py

@@ -1,3 +1,5 @@
+import importlib
 import logging
 
 logger = logging.getLogger(__name__)
+celery = getattr(importlib.import_module("adhocracy-plus.config.celery"), "celery")

changelog/7601.md

@@ -0,0 +1,4 @@
+## Added
+
+- adds support for celery task queues with a redis message broker
+

docs/celery.md

@@ -0,0 +1,21 @@
+
+## Background
+
+We want to upgrade Django from the current version to at least 4. But our current approach to running background tasks, namely `django-background-tasks` is no longer supported in Django 4. Hence, we decided to switch to celery for distributed tasks.
+
+
+## Developer Notes
+
+The celery configuration file is `adhocracy-plus/config/celery.py`. The celery app is identically configured for all environments and for simplicity we use a `Config` class inside `celery.py` instead of namespaced variables in Django settings files.
+
+Celery is set up to autodiscover tasks. To define a celery task simply import the celery app and use it to decorate the task function. Since the celery config file is located in a directory that uses a hyphen (`adhocracy-plus`) we use the `importlib` to import the app. For convenience, you can import celery from apps:
+
+```python
+from apps import celery
+
+@celery.task
+def celery_dummy_task():
+    print("hello")
+
+    return "world"
+```

requirements/base.txt

@@ -26,3 +26,7 @@ easy-thumbnails[svg]==2.8.5
 jsonfield==3.1.0
 python-dateutil==2.8.2
 rules==3.3
+
+# celery
+celery==5.3.1
+redis==5.0.0