Upgrade to v3.7 for docker-compose service definition

We were encountering issues when overriding service definitions with
"x-...". These were solved by upgrading docker-compose and switching to
3.7 service definition. As a consequence, the minimum supported docker
version is 18.06.0, as specified by
https://docs.docker.com/compose/compose-file/#compose-and-docker-compatibility-matrix

CHANGELOG.md

@@ -4,8 +4,9 @@ Note: Breaking changes between versions are indicated by "💥".
 
 ## Unreleased
 
+- [Improvement] Upgrade to the 3.7 docker-compose syntax
 - [Improvement] The `dev runserver` command can now be run for just any service
-- 💥[Feature] `dev run/exec` commands now support generic options which are passed to docker-compose. Consequently, defining the `TUTOR_EDX_PLATFORM_PATH` environment variable no longer works. Instead, users are encouraged to explicitely pass the `-v` option or define a command alias.
+- 💥[Feature] `dev run/exec` commands now support generic options which are passed to docker-compose. Consequently, defining the `TUTOR_EDX_PLATFORM_PATH` environment variable no longer works. Instead, users are encouraged to explicitely pass the `-v` option or define a command alias
 
 ## 3.9.1 (2020-01-08)
 

docs/install.rst

@@ -8,7 +8,7 @@ Requirements
 
 The only prerequisite for running this is a working docker installation. Both docker and docker-compose are required. Follow the instructions from the official documentation:
 
-- `Docker <https://docs.docker.com/engine/installation/>`_
+- `Docker <https://docs.docker.com/engine/installation/>`_: minimum supported version is 18.06.0.
 - `Docker compose <https://docs.docker.com/compose/install/>`_
 
 ⚠️ Warning: do not attempt to simply run ``apt-get install docker docker-compose`` on older Ubuntu platforms, such as 16.04 (Xenial), as you will get older versions of these utilities.

tutor/templates/dev/docker-compose.yml

@@ -1,17 +1,17 @@
-version: "3"
+version: "3.7"
+
+x-openedx-service:
+  &openedx-service
+  image: {{ DOCKER_REGISTRY }}{{ DOCKER_IMAGE_OPENEDX_DEV }}
+  environment:
+    SETTINGS: ${TUTOR_EDX_PLATFORM_SETTINGS:-tutor.development}
+  volumes:
+    # theme files
+    - ../build/openedx/themes:/openedx/themes
+    # editable requirements
+    - ../build/openedx/requirements:/openedx/requirements
 
 services:
-  x-openedx-service:
-    &openedx-service
-    image: {{ DOCKER_REGISTRY }}{{ DOCKER_IMAGE_OPENEDX_DEV }}
-    environment:
-      SETTINGS: ${TUTOR_EDX_PLATFORM_SETTINGS:-tutor.development}
-    volumes:
-      # theme files
-      - ../build/openedx/themes:/openedx/themes
-      # editable requirements
-      - ../build/openedx/requirements:/openedx/requirements
-
   lms:
     <<: *openedx-service
     command: ./manage.py lms runserver 0.0.0.0:8000

tutor/templates/local/docker-compose.yml

@@ -1,4 +1,4 @@
-version: "3"
+version: "3.7"
 services:
 
   ############# External services