Switch local service extension tactics

{{cookiecutter.project_slug}}/local.yml

@@ -5,7 +5,7 @@ volumes:
   postgres_backup_dev: {}
 
 services:
-  django:
+  django: &django
     build:
       context: .
       dockerfile: ./compose/django/Dockerfile-dev
@@ -28,7 +28,6 @@ services:
       - postgres_backup_dev:/backups
     environment:
       - POSTGRES_USER={{cookiecutter.project_slug}}
-
 {% if cookiecutter.use_pycharm == 'y' %}
   pycharm:
     build:
@@ -41,21 +40,19 @@ services:
     volumes:
       - .:/app
 {% endif %}
-
 {% if cookiecutter.use_mailhog == 'y' %}
   mailhog:
     image: mailhog/mailhog:v1.0.0
     ports:
       - "8025:8025"
 {% endif %}
-
-{% if cookiecutter.use_celery == 'y' -%}
+{% if cookiecutter.use_celery == 'y' %}
   redis:
-      image: redis:3.0
+    image: redis:3.0
 
   celeryworker:
-    extends:
-      service: django
+    # https://github.com/docker/compose/issues/3220
+    <<: *django
     depends_on:
       - redis
       - postgres{% if cookiecutter.use_mailhog == 'y' %}
@@ -63,11 +60,11 @@ services:
     command: /start-celeryworker-dev.sh
 
   celerybeat:
-    extends:
-      service: django
+    # https://github.com/docker/compose/issues/3220
+    <<: *django
     depends_on:
       - redis
       - postgres{% if cookiecutter.use_mailhog == 'y' %}
       - mailhog{% endif %}
     command: /start-celerybeat-dev.sh
-{%- endif %}
+{% endif %}