Allow the xqueue session engine and cache to be configurable.

CHANGELOG.md

+- Role: xqueue
+  - Added `XQUEUE_SESSION_ENGINE` to allow a configurable xqueue session engine.
+  - Added `XQUEUE_CACHES` to allow a configurable xqueue cache.
+
 - Role: devpi
   - New role added to configure a devpi service as a pass-through cache for PyPI.
 
@@ -15,7 +19,7 @@
 
 - Role: edxapp
   - Added `EDXAPP_FERNET_KEYS` to allow for use of django-fernet-keys in LMS.
-  
+
 - Role: edxapp
   - Added `EDX_PLATFORM_REVISION` (set from `edx_platform_version`). This is for
   edx-platform debugging purposes, and replaces calling dealer.git at startup.

playbooks/roles/xqueue/defaults/main.yml

@@ -59,6 +59,9 @@ XQUEUE_SETTINGS_MODULE: "xqueue.aws_settings"
 XQUEUE_WORKERS: !!null
 XQUEUE_WORKERS_PER_QUEUE: 12
 
+XQUEUE_SESSION_ENGINE: !!null
+XQUEUE_CACHES: !!null
+
 # Internal vars below this line
 #############################################
 
@@ -91,6 +94,8 @@ xqueue_env_config:
   RABBIT_PORT: "{{ XQUEUE_RABBITMQ_PORT }}"
   RABBIT_VHOST: "{{ XQUEUE_RABBITMQ_VHOST }}"
   RABBIT_TLS: "{{ XQUEUE_RABBITMQ_TLS }}"
+  SESSION_ENGINE: "{{ XQUEUE_SESSION_ENGINE }}"
+  CACHES: "{{ XQUEUE_CACHES }}"
   LOCAL_LOGLEVEL: "{{ XQUEUE_LOCAL_LOGLEVEL }}"
   UPLOAD_BUCKET: "{{ XQUEUE_UPLOAD_BUCKET }}"
   UPLOAD_PATH_PREFIX: "{{ XQUEUE_UPLOAD_PATH_PREFIX }}"