Makes the read preferences for content- and modulestore configurable

with sane defaults for Studio and LMS.

Also ensures that EDXAPP_MONGO_REPLICA_SET is included in all
docstore configuration blocks.

CHANGELOG.md

@@ -9,14 +9,21 @@
     your configuration to set `EDXAPP_CELERY_BROKER_TRANSPORT` explicitly.
 
 - Role: edxapp
-  - Added `EDXAPP_LMS_SPLIT_DOC_STORE_READ_PREFERENCE` with a default value of
-    SECONDARY_PREFERED to distribute read workload across the replica set.
-  - Changed `EDXAPP_MONGO_HOSTS` to be a comma seperated string, which is
-    required by pymongo.MongoReplicaSetClient for multiple hosts instead of an
-    array.
   - Added `EDXAPP_MONGO_REPLICA_SET`, which is required to use
-    pymongo.MongoReplicaSetClient in PyMongo 2.9.1, whis is required to use the
-    read_preference setting. This should be set to the name of your replica set.
+    pymongo.MongoReplicaSetClient in PyMongo 2.9.1.  This should be set to the
+    name of your replica set.
+    This setting causes the `EDXAPP_*_READ_PREFERENCE` settings below to be used.
+  - Added `EDXAPP_MONGO_CMS_READ_PREFERENCE` with a default value of `PRIMARY`.
+  - Added `EDXAPP_MONGO_LMS_READ_PREFERENCE` with a default value of
+    `SECONDARY_PREFERED` to distribute the read workload across the replica set
+    for replicated docstores and contentstores.
+  - Added `EDXAPP_LMS_SPLIT_DOC_STORE_READ_PREFERENCE` with a default value of
+    `EDXAPP_MONGO_LMS_READ_PREFERENCE`.
+  - Added `EDXAPP_LMS_DRAFT_DOC_STORE_CONFIG` with a default value of
+    `EDXAPP_MONGO_CMS_READ_PREFERENCE`, to enforce consistency between
+    Studio and the LMS Preview modes.
+  - Removed `EDXAPP_CONTENTSTORE_ADDITIONAL_OPTS`, since there is no notion of
+    common options to the content store anymore.
 
 - Role: nginx
   - Modified `lms.j2` , `cms.j2` , `credentials.j2` , `edx_notes_api.j2` and `insights.j2` to enable HTTP Strict Transport Security

playbooks/roles/edxapp/defaults/main.yml

@@ -65,8 +65,7 @@ EDXAPP_XQUEUE_DJANGO_AUTH:
   password: 'password'
 EDXAPP_XQUEUE_URL: 'http://localhost:18040'
 
-# EDXAPP_MONGO_HOSTS must be a comma seperated list of hosts/ips for
-# compatibility with pymongo.MongoReplicaSetClient in PyMongo 2.9.1
+# Comma-separated list of hosts/ips
 EDXAPP_MONGO_HOSTS: 'localhost'
 EDXAPP_MONGO_PASSWORD: 'password'
 EDXAPP_MONGO_PORT: 27017
@@ -74,7 +73,14 @@ EDXAPP_MONGO_USER: 'edxapp'
 EDXAPP_MONGO_DB_NAME: 'edxapp'
 EDXAPP_MONGO_USE_SSL: False
 EDXAPP_MONGO_REPLICA_SET: ''
-EDXAPP_LMS_SPLIT_DOC_STORE_READ_PREFERENCE: 'SECONDARY_PREFERRED'
+# Used only if EDXAPP_MONGO_REPLICA_SET is provided.
+EDXAPP_MONGO_CMS_READ_PREFERENCE: 'PRIMARY'
+EDXAPP_MONGO_LMS_READ_PREFERENCE: 'SECONDARY_PREFERRED'
+# We use the CMS read_preference here because the draft docstore's view of
+# the modulestore should mirror Studio's, so that instructors can check their
+# changes in Preview mode.
+EDXAPP_LMS_DRAFT_DOC_STORE_READ_PREFERENCE: '{{ EDXAPP_MONGO_CMS_READ_PREFERENCE }}'
+EDXAPP_LMS_SPLIT_DOC_STORE_READ_PREFERENCE: '{{ EDXAPP_MONGO_LMS_READ_PREFERENCE }}'
 
 EDXAPP_MYSQL_DB_NAME: 'edxapp'
 EDXAPP_MYSQL_USER: 'edxapp001'
@@ -851,9 +857,24 @@ edxapp_environment_extra: {}
 
 edxapp_environment: "{{ edxapp_environment_default | combine(edxapp_environment_extra) }}"
 
+edxapp_generic_contentstore_config: &edxapp_generic_default_contentstore
+  ENGINE:  'xmodule.contentstore.mongo.MongoContentStore'
+  #
+  # connection strings are duplicated temporarily for
+  # backward compatibility
+  #
+  OPTIONS:
+    db: "{{ EDXAPP_MONGO_DB_NAME }}"
+    host: "{{ EDXAPP_MONGO_HOSTS }}"
+    password: "{{ EDXAPP_MONGO_PASSWORD }}"
+    port: "{{ EDXAPP_MONGO_PORT }}"
+    user: "{{ EDXAPP_MONGO_USER }}"
+    ssl: "{{ EDXAPP_MONGO_USE_SSL }}"
+
 edxapp_generic_doc_store_config: &edxapp_generic_default_docstore
   db: "{{ EDXAPP_MONGO_DB_NAME }}"
   host: "{{ EDXAPP_MONGO_HOSTS }}"
+  replicaSet: "{{ EDXAPP_MONGO_REPLICA_SET }}"
   password: "{{ EDXAPP_MONGO_PASSWORD }}"
   port: "{{ EDXAPP_MONGO_PORT }}"
   user: "{{ EDXAPP_MONGO_USER }}"
@@ -864,17 +885,17 @@ edxapp_generic_doc_store_config: &edxapp_generic_default_docstore
   connectTimeoutMS: 2000 # default is 20000, I believe raises pymongo.errors.ConnectionFailure
   # Not setting waitQueueTimeoutMS and waitQueueMultiple since pymongo defaults to nobody being allowed to wait
 
-
 EDXAPP_LMS_DRAFT_DOC_STORE_CONFIG:
   <<: *edxapp_generic_default_docstore
+  read_preference: "{{ EDXAPP_LMS_DRAFT_DOC_STORE_READ_PREFERENCE }}"
 
 EDXAPP_LMS_SPLIT_DOC_STORE_CONFIG:
   <<: *edxapp_generic_default_docstore
-  replicaSet: "{{ EDXAPP_MONGO_REPLICA_SET }}"
   read_preference: "{{ EDXAPP_LMS_SPLIT_DOC_STORE_READ_PREFERENCE }}"
 
 EDXAPP_CMS_DOC_STORE_CONFIG:
   <<: *edxapp_generic_default_docstore
+  read_preference: "{{ EDXAPP_MONGO_CMS_READ_PREFERENCE }}"
 
 edxapp_databases:
 # edxapp's edxapp-migrate scripts and the edxapp_migrate play
@@ -929,26 +950,10 @@ edxapp_generic_auth_config:  &edxapp_generic_auth
   SWIFT_TEMP_URL_KEY: "{{ EDXAPP_SWIFT_TEMP_URL_KEY }}"
   SWIFT_TEMP_URL_DURATION: "{{ EDXAPP_SWIFT_TEMP_URL_DURATION }}"
   SECRET_KEY:  "{{ EDXAPP_EDXAPP_SECRET_KEY }}"
-  DOC_STORE_CONFIG: "{{ edxapp_generic_doc_store_config }}"
   XQUEUE_INTERFACE:
     basic_auth: "{{ EDXAPP_XQUEUE_BASIC_AUTH }}"
     django_auth: "{{ EDXAPP_XQUEUE_DJANGO_AUTH }}"
     url: "{{ EDXAPP_XQUEUE_URL }}"
-  CONTENTSTORE:
-    ENGINE:  'xmodule.contentstore.mongo.MongoContentStore'
-    #
-    # connection strings are duplicated temporarily for
-    # backward compatibility
-    #
-    OPTIONS:
-      db: "{{ EDXAPP_MONGO_DB_NAME }}"
-      host: "{{ EDXAPP_MONGO_HOSTS }}"
-      password: "{{ EDXAPP_MONGO_PASSWORD }}"
-      port: "{{ EDXAPP_MONGO_PORT }}"
-      user: "{{ EDXAPP_MONGO_USER }}"
-      ssl: "{{ EDXAPP_MONGO_USE_SSL }}"
-    ADDITIONAL_OPTIONS: "{{ EDXAPP_CONTENTSTORE_ADDITIONAL_OPTS }}"
-    DOC_STORE_CONFIG: *edxapp_generic_default_docstore
   DATABASES: "{{ edxapp_databases }}"
   EMAIL_HOST_USER: "{{ EDXAPP_EMAIL_HOST_USER }}"
   EMAIL_HOST_PASSWORD: "{{ EDXAPP_EMAIL_HOST_PASSWORD }}"
@@ -1166,6 +1171,11 @@ generic_env_config:  &edxapp_generic_env
 
 lms_auth_config:
   <<: *edxapp_generic_auth
+  CONTENTSTORE:
+    <<: *edxapp_generic_default_contentstore
+    ADDITIONAL_OPTIONS: "{{ EDXAPP_CONTENTSTORE_ADDITIONAL_OPTS }}"
+    DOC_STORE_CONFIG: "{{ EDXAPP_LMS_SPLIT_DOC_STORE_CONFIG }}"
+  DOC_STORE_CONFIG: "{{ EDXAPP_LMS_SPLIT_DOC_STORE_CONFIG }}"
   SEGMENT_KEY: "{{ EDXAPP_LMS_SEGMENT_KEY }}"
   OPTIMIZELY_PROJECT_ID: "{{ EDXAPP_OPTIMIZELY_PROJECT_ID }}"
   EDX_API_KEY: "{{ EDXAPP_EDX_API_KEY }}"
@@ -1256,7 +1266,11 @@ lms_env_config:
 
 cms_auth_config:
   <<: *edxapp_generic_auth
-  SEGMENT_KEY: "{{ EDXAPP_CMS_SEGMENT_KEY }}"
+  CONTENTSTORE:
+    <<: *edxapp_generic_default_contentstore
+    ADDITIONAL_OPTIONS: "{{ EDXAPP_CONTENTSTORE_ADDITIONAL_OPTS }}"
+    DOC_STORE_CONFIG: "{{ EDXAPP_CMS_DOC_STORE_CONFIG }}"
+  DOC_STORE_CONFIG: "{{ EDXAPP_CMS_DOC_STORE_CONFIG }}"
   MODULESTORE:
     default:
         ENGINE: 'xmodule.modulestore.mixed.MixedModuleStore'
@@ -1277,6 +1291,7 @@ cms_auth_config:
                 default_class: 'xmodule.hidden_module.HiddenDescriptor'
                 fs_root:  "{{ edxapp_course_data_dir }}"
                 render_template: 'edxmako.shortcuts.render_to_string'
+  SEGMENT_KEY: "{{ EDXAPP_CMS_SEGMENT_KEY }}"
   PARSE_KEYS: "{{ EDXAPP_PARSE_KEYS }}"
 
 cms_env_config: