Relocating for compose networking conventions, net will be edx in this case.

docker/compose/edx/docker-compose.yml

@@ -4,27 +4,18 @@ db:
   environment:
     - MYSQL_ROOT_PASSWORD=''
   hostname: db
-  dns:
-    - 172.19.0.3
-    - 8.8.8.8
   ports:
     - 3306:3306
 
 mongo:
   container_name: mongo
   image: edxops/mongo:v2
-  dns:
-    - 172.19.0.3
-    - 8.8.8.8
   volumes: 
     - /var/devstack/mongo/data:/data
 
 es:
   container_name: es
   image: edxops/elasticsearch:v1
-  dns:
-    - 172.19.0.3
-    - 8.8.8.8
   volumes:
     - /tmp/elasticsearch/data:/es-data
 
@@ -38,9 +29,6 @@ forums:
   image: edxops/forums:opencraft
   ports:
     - 4567:4567
-  dns:
-    - 172.19.0.3
-    - 8.8.8.8
   volumes:
     - /home/edward/Documents/git/edx/configuration:/edx/app/edx_ansible/edx_ansible