Adds ability to have multiple read replicas. (#116)

* Adds ability to have multiple read replicas.

* Adds ability to have dynamic number of read replicas.

Author: esirK

sensorsafrica/api/v2/serializers.py

@@ -1,7 +1,6 @@
 from rest_framework import serializers
 from feinstaub.sensors.serializers import (
     NestedSensorLocationSerializer,
-    NestedSensorTypeSerializer,
 )
 from feinstaub.sensors.models import Node, Sensor, SensorType, SensorLocation
 from feinstaub.sensors.serializers import (VerboseSensorDataSerializer, )

sensorsafrica/router.py

@@ -1,10 +1,15 @@
+import random
+
+from django.conf import settings
+
 class ReplicaRouter:
-    route_app_labels = {'auth', 'sessions',}
+    read_replica_app_labels = {'sensors', }
+    read_replicas = list(settings.DATABASES.keys() - {'default', })
 
     def db_for_read(self, model, **hints):
-        if model._meta.app_label in self.route_app_labels:
-            return 'default'
-        return "read_replica"
+        if model._meta.app_label in self.read_replica_app_labels:
+            return random.choice(self.read_replicas)
+        return 'default'
 
     def db_for_write(self, model, **hints):
         return "default"

sensorsafrica/settings.py

@@ -109,14 +109,13 @@
     "SENSORSAFRICA_DATABASE_URL",
     "postgres://sensorsafrica:sensorsafrica@localhost:5432/sensorsafrica",
 )
-READ_DATABASE_URL = os.getenv(
-    "SENSORSAFRICA_READ_DATABASE_URL", DATABASE_URL
-)
 
-DATABASES = {
-                "default": dj_database_url.parse(DATABASE_URL),
-                "read_replica": dj_database_url.parse(READ_DATABASE_URL),
-            }
+READ_DATABASE_URLS = os.getenv("SENSORSAFRICA_READ_DATABASE_URLS", DATABASE_URL).split(" ")
+
+DATABASES = {"default": dj_database_url.parse(DATABASE_URL), }
+
+for index, read_database_url in enumerate(1, READ_DATABASE_URLS):
+    DATABASES[f"read_replica_{index}"] = dj_database_url.parse(read_database_url)
 
 DATABASE_ROUTERS = ["sensorsafrica.router.ReplicaRouter", ]