Fix read replicas (#122)

* fix loading database urls

* modify db router allow_relation method

* remove app label in router

* add file based session management

* update router.py read replicas

* fix custom migration by specifying default db

* using schema editor to define migration db

* update migration schema editor connection

* update migration schema editor connection

* update migration schema editor connection

Author: thepsalmist

docker-compose.yml

@@ -26,7 +26,7 @@ services:
       context: .
     environment:
       SENSORSAFRICA_DATABASE_URL: postgres://sensorsafrica:sensorsafrica@postgres:5432/sensorsafrica
-      SENSORSAFRICA_READ_DATABASE_URL: postgres://sensorsafrica:sensorsafrica@postgres:5432/read_replica
+      SENSORSAFRICA_READ_DATABASE_URLS: postgres://sensorsafrica:sensorsafrica@postgres:5432/sensorsafrica
       SENSORSAFRICA_RABBITMQ_URL: amqp://sensorsafrica:sensorsafrica@rabbitmq//
       SENSORSAFRICA_FLOWER_ADMIN_USERNAME: admin
       SENSORSAFRICA_FLOWER_ADMIN_PASSWORD: password

sensorsafrica/openstuttgart/feinstaub/sensors/migrations/0011_auto_20150807_1927.py

@@ -12,12 +12,14 @@ def migrate_sensor(apps, schema_editor):
     # if we directly import it, it'll be the wrong version
     Sensor = apps.get_model("sensors", "Sensor")
     Node = apps.get_model("sensors", "Node")
-    for sensor in Sensor.objects.all():
-        print("sensor: {}".format(sensor.id))
-        node = Node.objects.create(uid=sensor.uid,
-                                   description=sensor.description,
-                                   owner=sensor.owner,
-                                   location=sensor.location)
+    db_alias = schema_editor.connection.alias
+    if db_alias != "default":
+        return
+    for sensor in Sensor.objects.using(db_alias).all():
+        node = Node.objects.using(db_alias).create(uid=sensor.uid,
+                                description=sensor.description,
+                                owner=sensor.owner,
+                                location=sensor.location)
         sensor.node = node
         sensor.save()
 

sensorsafrica/router.py

@@ -3,14 +3,11 @@
 from django.conf import settings
 
 class ReplicaRouter:
-    read_replica_app_labels = {'sensors', }
-    read_replicas = list(settings.DATABASES.keys() - {'default', })
+    read_replicas = settings.READ_DATABASE_URLS
 
     def db_for_read(self, model, **hints):
-        if model._meta.app_label in self.read_replica_app_labels:
-            return random.choice(self.read_replicas)
-        return 'default'
-    
+        return random.choice(self.read_replicas)
+        
     def db_for_write(self, model, **hints):
         return "default"
 

sensorsafrica/settings.py

@@ -101,6 +101,7 @@
 
 WSGI_APPLICATION = "sensorsafrica.wsgi.application"
 
+SESSION_ENGINE = "django.contrib.sessions.backends.file"
 
 # Database
 # https://docs.djangoproject.com/en/1.10/ref/settings/#databases