Add central configuration by python modules

Configuration module is loaded from environment variable
OGN_CONFIG_MODULE, defaults to "config/defaults.py".

README.md

@@ -93,6 +93,14 @@ The following scripts run in the foreground and should be deamonized
   celery -A ogn.collect worker -l info
   ```
 
+To load a custom configuration, create a file `myconfig.py` (see [config/default.py](config/default.py))
+and set the environment variable `OGN_CONFIG_MODULE` accordingly.
+
+```
+export OGN_CONFIG_MODULE="myconfig.py"
+./manage.py gateway.run
+```
+
 ### manage.py - CLI options
 ```
 usage: manage.py [<namespace>.]<command> [<args>]

config/default.py

@@ -0,0 +1,4 @@
+SQLALCHEMY_DATABASE_URI = 'sqlite:///beacons.db'
+
+BROKER_URL = 'redis://localhost:6379/0'
+CELERY_RESULT_BACKEND = 'redis://localhost:6379/0'

ogn/collect/celery.py

@@ -1,21 +1,19 @@
+import os
+import importlib
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
 
 from celery import Celery
 from celery.signals import worker_init, worker_shutdown
 
-app = Celery('ogn.collect',
-             broker='redis://localhost:6379/0',
-             backend='redis://localhost:6379/0',
-             include=["ogn.collect.database", "ogn.collect.logbook"])
-
-DB_URI = 'sqlite:///beacons.db'
+os.environ.setdefault('OGN_CONFIG_MODULE', 'config.default')
+config = importlib.import_module(os.environ['OGN_CONFIG_MODULE'])
 
 
 @worker_init.connect
 def connect_db(signal, sender):
     # Load settings like DB_URI...
-    engine = create_engine(DB_URI, echo=False)
+    engine = create_engine(config.SQLALCHEMY_DATABASE_URI, echo=False)
 
     Session = sessionmaker(bind=engine)
     sender.app.session = Session()
@@ -26,5 +24,8 @@ def close_db(signal, sender):
     sender.app.session.close()
 
 
-if __name__ == '__main__':
-    app.start()
+app = Celery('ogn.collect',
+             include=["ogn.collect.database",
+                      "ogn.collect.logbook"])
+
+app.config_from_envvar("OGN_CONFIG_MODULE")

ogn/commands/dbutils.py

@@ -1,6 +1,13 @@
+import os
+import importlib
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
-engine = create_engine('sqlite:///beacons.db', echo=False)
+
+
+os.environ.setdefault('OGN_CONFIG_MODULE', 'config.default')
+
+config = importlib.import_module(os.environ['OGN_CONFIG_MODULE'])
+engine = create_engine(config.SQLALCHEMY_DATABASE_URI, echo=False)
 
 Session = sessionmaker(bind=engine)
 session = Session()